Biology Unit 5

transpiration

the process by which a plant loses water to the atmosphere through the surfaces of its leaves

5.22 Pollution Pollution take many forms. When people work together, they can reverse its effects. Pollution of air, water, and land negatively affects ecosystems and can be corrected.

Pollution is defined as a contamination, especially of air or water. Pollution negatively affects humans and other living things. Cleaning up pollution can be extremely difficult and restoration can be a daunting task, but people have succeeded in cleaning up pollution—in many instances, restoring polluted areas to a more balanced state.

The introduction of a nonnative, invasive species into an ecosystem can disturb the natural balance within the system. Native organisms rely on algae as sources of food. Zebra mussels compete with native organisms for the algae present in the water. They are so good at filtering the algae out of the water that native organisms cannot compete, which interferes with the food that exists in the ecosystem. Zebra Mussels If you'd like to learn more about zebra mussels and how they are affecting aquatic ecosystems, visit these websites: Lake Michigan Food Web Progression of the Zebra Mussel FAQs About the Zebra Mussel

The United States spends over $120 billion a year to manage the damaging effects of invasive species. Invasive species are organisms that have invaded established ecosystems. Through the actions of human travel and trade, new, nonnative species have arrived in North America. How do invasive species change an ecosystem? By changing the food web significantly, these organisms alter the structure of an ecosystem. Zebra mussels (Dreissena polymorpha) first arrived in Lake Michigan in the late 1980s. They most likely made their way to Lake Michigan as hitchers on cargo ships. Zebra mussels are filter feedersthat remove algae from the water.

Photosynthesis removes carbon dioxide and generates sugars containing carbon.

Walking down the street, a young girl stops under a sugar maple tree. Gazing up, she notices the intricacy and elegance of this tree as the lobed leaves flutter in a passing breeze. Without realizing it, the girl's connection with the tree goes beyond her peaceful stroll. Together, the girl and tree—and millions of other living things—are part of the carbon cycle. The carbon dioxide from her breath rises and enters the leaves, where it becomes converted into glucose (a carbon-based sugar) through the process of photosynthesis Opens in modal popup window . The carbon will remain stored there until it is released through other processes.

greenhouse effect

the process in which the atmosphere reflects radiation bouncing off earth´s surface

respiration

the processes in which an organism exchanges gases with its environment

biosphere

the zone of life on the earth that includes all living things

abiotic

nonbiological

secondary succession

succession that occurs where vegetation existed previously

dentrification

the conversion of nitrate to gaseous nitrogen, which then enters the atmosphere

exponential growth

unchecked reproduction of a populaton of organisms

Rachel Carson-Waking up the World

American biologist Rachel Carson was largely responsible for drawing public attention to the dangers of DDT and other toxic chemicals. Her book Silent Spring, first published in 1962 as a serial in the New Yorker Magazine, presented data that suggested that DDT was responsible for bird deaths all over the country. When DDT was eventually banned for agricultural use, the even signaled the beginning of today's environmental movement.

Denitrifying bacteria convert nitrates into nitrogen gas. A Reminder: Turn to pages 206-207 of your reference book to see how denitrification fits into the overall nitrogen cycle.

By now you've learned that there is a bacterium for practically anything, which is why scientists love to study and use bacteria. Bacteria break down garbage, digest food in your small intestine, and convert nitrogen gas into nitrates and ammonia that you can use. Other bacteria convert those nitrates and ammonia back into nitrogen gas through the process of denitrification Opens in modal popup window . Found where oxygen is lacking, denitrifying bacteria use nitrogen compounds instead of oxygen for their processes of respiration. In doing so, they convert excess ammonia and nitrates back into the common atmospheric nitrogen gas (N2), where the cycle begins anew. Unwittingly, every action by every living thing keeps substances on earth cycling and cycling.

5.07 Energy Flow in Ecosystems After plants produce usable chemical energy from sunlight, energy flows through ecosystems from one level to the next. sun's energy---producers---consumers examples include herbivores and carnivores

Energy fuels life. Starting with its conversion from light energy to chemical energy in photosynthesis, chemical energy passes through each level of an ecosystem, one organism at a time. Stored in the form of food, usable chemical energy for living things passes from one organism to the next, until all the energy is consumed or lost as heat. The available supply of energy continues to be renewed through photosynthesis.

5.08 Food Chains and Food Webs Food chains and food webs illustrate pathways of energy flow within ecosystems. ecosystem---energy moves through food chains within a food web and energy is lost at each trophic level.

Grass uses the sun to make food. A grasshopper eats the grass, and the grasshopper is then eaten by a bird. A beetle also feeds on the grass and then falls prey to a spider. Imagine how confusing it would be to study the flow of energy in ecosystems if it all had to be written out in sentences. Scientists have developed simple models that illustrate this energy flow: food chains and food webs.

Nitrogen-Fixing Bacteria

Not all nitrogen-fixing bacteria live within the tissues of plants. Some live freely in the soil.

Nitrogen is needed to make protein and DNA.

Review how nitrogen is returned to the soil by electrical effects in thunderstorms, by the addition of fertilizer, and by bacterial action. Transcript (Video with Audio Description) Screen 1 00:00:00.00 Description: There is an animation of the periodic table. The nitrogen block is enlarged and begins to rotate. A rotating earth is in the background. Female Narrator: Nitrogen is an essential element for plants and animals. It's needed to make protein and DNA. Seventy-eight percent of the atmosphere is nitrogen gas, but nitrogen is very unreactive and can't be used directly by plants or animals. It needs to be converted into nitrates before most plants can use it. 00:00:34.00 Description: A combine moves down a wheat field. Female Narrator: Nitrates in the soil are absorbed by the roots of plants, which then build them up into complex proteins. These tomato plants have been grown in different concentrations of nitrate solution for the same amount of time, but they look quite different. 00:00:54.00 Description: There are three clear containers filled with liquid. The container on the left is labeled 1 times N O, subscript, 3, baseline, superscript, negative sign, baseline. The container in the middle is labeled one-half times N O, subscript, 3, baseline, superscript, negative sign, baseline. The container on the right is labeled N O, subscript, 3, baseline, superscript, negative sign, baseline. That label has an X over it. The container on the left has a large tomato plant with many dark-green leaves and many roots. The container in the middle has a medium-sized tomato plant with fewer, paler leaves and fewer roots. The container on the right has a small tomato plant with few leaves and roots. Female Narrator: With enough nitrate, the plant is healthy. It's grown tall and bushy. As the nitrate concentration decreases, so too does the health of the plant. So where does the nitrate present in the soil come from? 00:02:02.00 Description: There is a lightning storm at night. An animation shows N, subscript 2, baseline, arrow, N O, subscript 3, baseline, superscript negative sign, baseline. Female Narrator: Lightning provides a small amount. It converts nitrogen gas present in the atmosphere directly into nitrates. A more reliable way of increasing the nitrate content of soil is to add fertilizer. Inorganic fertilizer contains nitrates, which can be absorbed by plants straightaway. Organic fertilizer, like manure, contains dead animal and plant material. As it decays, it releases nitrogen compounds into the soil. 00:02:54.00 Description: A tractor drives over plowed farmland, spreading small white pellets. A truck spreads manure on a field. Female Narrator: A range of bacteria break down the proteins in manure and convert them to ammonium compounds. Ammonium ions contain nitrogen and hydrogen. But for most plants to be able to build up proteins, these need to be converted to nitrates. This is carried out by nitrifying bacteria. 00:03:22.00 Description: The reaction is N H, subscript, 4, baseline, superscript, positive sign, baseline, arrow, N O, subscript 3, baseline, superscript, negative sign, baseline. There is a second reaction: N, subscript, 2, baseline, arrow N O, subscript, 3, baseline, superscript, negative sign. Female Narrator: Another process involves nitrogen-fixing bacteria. These take up atmospheric nitrogen. Nitrogen-fixing bacteria exist free in the soil or in the roots of certain plants, like clover. Special nitrogen-fixing bacteria, called rhizobium, live in tiny nodules on the roots. The bacteria convert atmospheric nitrogen into ammonium ions, and eventually proteins. 00:04:22.00 Description: A tractor drives through a field. There is a close-up of a clover leaf, then a close-up of the roots. The root has small nodules. One side of the root is held with a tweezers, and the root on the other side of the nodules is cut with a scissors. The nodules are placed in a petri dish and bleach is poured over them. A scientist swishes around the bleach in the petri dish. Female Narrator: To show the existence of these bacteria, the outer surface of the nodules must first be sterilized, so that only the rhizobium bacteria inside the nodule are alive. After washing in bleach and rinsing with water, a glass rod is used to crush the nodules and liberate the bacteria inside. A loop of wire is heated in a flame to make it completely sterile. It's then dipped into the bacteria and transferred to a sterile plate containing agar. After a few days' incubation, the rhizobium has multiplied and is now visible. 00:05:33.00 Description: The scientist rubs the loop of wire over the agar. The scientist removes the lid of the petri dish. The rhizobium is visible as a raised pink growth on the agar plate.

Local governments, businesses, and citizen groups can take action concerning global warming on their own.

Several states, cities, and citizen groups across the United States have agreed to the reduction levels outlined in the Kyoto Protocol. Based on their interpretation of scientific data and consideration of all other factors, these groups have felt compelled to work to reduce emissions of certain gases that arise from human activity. In many cases, local governments working with local businesses have pledged to reduce carbon emissions. California, one of the largest emitters of greenhouse gases, has set very strict limits on emissions from vehicles and industry. Global warming town hall State, local, and citizen groups often hold public forums that present scientific data as part of discussions of environmental issues, among others.

Scientific studies can provide data to people who make decisions. More on Mauna Loa Detailed observations and measurements of concentrations of carbon dioxide in the atmosphere began on Mauna Loa volcano on the Hawaiian island of Molokai in 1958. The project is the longest-running such study anywhere. The remoteness of the volcano and virtual lack of major industrial, agricultural, and other human activities that might influence local carbon dioxide concentrations make it the ideal site for studying long-term trends. The research data taken during the period 1959-2004 indicates a 19.4 percent increase in the annual mean concentration of carbon dioxide.

What happens when people disagree about major issues such as whether there is global warming and what causes it? How can citizens, industry leaders, and government officials get accurate information for making rational decisions? Scientists employing scientific methods can inform decision makers faced with difficult issues. The scientific process—including sharing results—ensures an objective analysis of any information sent through its rigorous multistep process. To review what you learned about scientific methods, turn to pages 10-11 of your reference book. Mauna Loa Since the late 1950s, carefully controlled scientific observations atop Hawaii's Mauna Loa volcano have precisely documented increases in atmospheric concentrations of carbon dioxide.

dark clouds

With a population of more than 20 million people, Mexico City is one of the largest cities in the world, and it suffers from chronic air pollution. The pollution around Mexico City is so constant and bad that schoolchildren there usually color pictures of the sky gray or brown, rather than blue.

climax community

a stable, long-lasting community that results from succession

comminuty

all of the populations that live and interact with each other in a particular area

primary succession

the change in species composition in a defined area over time, starting on ground that has no living things on it

biodiversity

the different kinds of species and total number of individuals of each species living in a defined area

producer

the ecological term applied to plants and other photosynthetic organisms that produce glucose

carrying capacity

the maximum population size that an area can support stably over time

food chain

the pathway along which food is transferred from one organism to another

Changes to ecosystems often occur because of climate change or human activity.

All ecosystems exist as a balance between biotic and abiotic factors. Complex food webs exist based on all these factors. When an ecosystem is altered, through a change to either a biotic or an abiotic factor, a change to the entire system often results. Ecosystems are indeed systems—meaning that all parts of the system are interconnected in some way. Two major causes of change to ecosystems are climate change and human activity. Laws now exist to protect some ecosystems.

Old, abandoned farmland and fields are other examples of secondary succession.

A farmer in Michigan decides to donate his land to the state for use as a forest preserve. Since it has been tilled and farmed for years, the land, which was once forest, presently consists of fields bordered by forests. Once the field is left alone, secondary succession begins. In what could be compared with a very slow march, the forest slowly reclaims the field. Along the edge of the field, seedlings grow into saplings, which grow into trees, which attract species of birds and mammals. Eventually, the field may resemble the original forest that the farmer's ancestors cut down. Through secondary succession, the forest has taken over the field. Farm Succession Abandoned farms and fields are frequently reclaimed by native ecosystems. This reclamation occurs through secondary succession.

Succession occurs when an ecosystem transforms because of the replacement of some species by others or the introduction of living things to an area previously devoid of life.

A hillside buried in volcanic ash, a newly formed island in the middle of the ocean, or a recently revealed field of rock represents areas where little to no life exists. Through primary succession, little by little, the space becomes a complex ecosystem. A pond, an abandoned field, or an ecosystem invaded by nonnative organisms undergo secondary succession to develop into a climax community. Ecosystems have their own unique climax communities. Whether natural or human-made, when species move in to replace others, it is called succession.

An ecosystem consists of biotic and abiotic factors.

A timid kangaroo rat jumps quickly from stone to stone on constant alert for resident snakes, hawks, and foxes. Like most desert organisms, the kangaroo rat prefers the cool night to be out and about, avoiding the scorching sun. Like other members of this Arizona desert community, the kangaroo rat lives on very little water. The sand, scarcity of water, hot air, and rocky abodes are some of the nonliving elements that the desert organisms share. Scientists have specific terms for the living and nonliving parts of an ecosystem: Living things are biotic Opens in modal popup window factors. Nonliving things are abiotic Opens in modal popup window factors.

Children help reforest clear-cut land in Costa Rica. Kids Saving the Rain Forest To learn more about Kids Saving the Rain Forest, visit the group's website, which is listed in the Lesson Resources under Lesson Links.

Anyone familiar with rain forests knows how diverse and interesting they are as living things (as are their inhabitants). In many areas, however, rain forests are being cleared for use as agricultural land. One such area in Costa Rica has a different fate—a hopeful one. Private citizens, motivated to be a part of a solution, purchased a large area of clear-cut rain forest, and together with a group called Kids Saving the Rain Forest are replanting tropical trees. Their goal: to plant 18,000 trees and reforest 50 hectares (123 acres) of land. Missing Metadata Private citizens are working to save rain forests.

Of earth's resources, some are renewable and others are not. natural resources are renewable like air, water, sun, wind, plants, and animals or nonrenewable like oil, coal, gas, and minerals.

As you near the end of the course, perhaps you've been inspired by your increased knowledge of biology to care just a bit more about earth. Every single solid, liquid, and gas thing you use comes from earth's resources. Some resources can be renewed, while others cannot. The quality of your life depends on the continued availability of those resources. Just look around and ask: What could you live without?

The disappearance of a pond is an example of secondary succession. Pond Successio Natural ponds are formed as streams and rivers change their course, as beavers construct dams, and as glaciers recede leaving behind pools of water. Over time, secondary succession occurs in the pond ecosystem. Here you will study succession in an abandoned Rocky Mountain beaver pond. The organisms present in and around the pond slowly affect the ecosystem, and changes occur. Wind, birds, and sometimes humans bring seeds to the pond. Fast-growing bushes such as willows establish themselves along the banks. Aquatic grasses grow in the sediment on the bottom of the pond. As organisms in the pond and along the shore die, organic matter is added to the bottom of the pond. Slowly, that sediment begins to fill in the pond. As the sediment continues to build up on the bottom of the pond, slow-growing hardwood trees compete for space and light on the banks of the pond. Lilly pads spread out on the surface of the pond and shade the aquatic grasses below. Secondary succession occurs as one group of organisms replaces another. Succession continues as dead plant material is continually added to the pond sediment. As hardwood evergreens begin to dominate the rich soils on the banks of the pond, they outcompete bushes and shrubs for sunlight. As the pond continues to fill in, succession continues. The aquatic ecosystem is slowly replaced by a terrestrial ecosystem. The process continues as the habitat changes. As abiotic factors change, a succession of biotic communities dominates the ecosystem. Eventually, a climax community is established. If abiotic and biotic factors in the ecosystem do not change, the climax community remains stable over time. The change that occurs in a pond is a classic example of secondary succession.

Attracted to the clear water of an inland pond, birds unknowingly bring in seed-containing droppings that one day will lead to changes in this aquatic habitat. As seeds arrive by wind or animal, they begin to take root at the edge and in the bottom of the pond. Over time, the plants encroach from the outside toward the center and from the bottom toward the surface. This encroachment slowly transforms the pond into a marsh. As succession continues, the marsh eventually transforms to soil-filled land. While this process may take hundreds of years, it is an example of secondary succession because new organisms are replacing others within the same area. Explore this example of secondary succession: Pond Succession

Secondary succession can begin after an extreme natural event.

Burning furiously, the Yellowstone fire burned extremely hot. Because it spread high into the treetops, even the oldest and tallest trees fell victim to the blaze. Both abiotic factors and biotic factors were suddenly changed. With the producers gone and hot ash covering the topsoil, most animals needed to abandon the area. It will take decades for those same trees to grow large enough to resemble the original forest. Until then, there will be a series of changes in the ecosystem that had supported the diverse animals of Yellowstone National Park. In the following screens, you'll step through secondary succession in a forest. Forest immediately after a fire A canopy fire can reduce a forest to ashes, but topsoil under the ashes allows secondary succession to begin.

In 1997, the United Nations sponsored the Kyoto Protocol, an international commitment to reduce carbon emissions.

By 1997, the rise in atmospheric temperatures had become such a worldwide concern that representatives from many countries met in Kyoto, Japan, to discuss how to decrease carbon emissions. Based primarily on the latest scientific data, an agreement was drafted and 84 countries, including the United States, signed it. The agreement set standards for how much each country should lower its emissions by a target date of 2012. The agreement is called the Kyoto Protocol. However, before the protocol's regulations were set to start in February 2005, the major countries involved continued to debate the protocol and some withdrew support. That debate is still going on: Some people think the protocol should have tougher regulations, and others think it should be less stringent.

While the oxygen cycle on earth largely involves photosynthesis and cellular respiration, other processes play lesser roles. Oxygen Cycle: In plants and animals, oxygen is removed from the atmosphere during cellular respiration. During photosynthesis, plants of all kinds release oxygen into earth's atmosphere Ninety percent of earth's oxygen is stored in the minerals of the earth's crust and mantle. It may be released through weathering. When organisms decay, oxygen is absorbed and carbon dioxide is released. The process of weathering rocks and minerals can either release oxygen or remove it from the atmosphere. The hard shells of marine animals contain large amounts of oxygen that are released through weathering after the animals die. Through photolysis, oxygen gas is released into the atmosphere when light energy breaks apart water or nitrate molecules.

Carbon is a key element for all living things on earth. Like other abiotic factors, carbon cycles and recycles between earth's soil, atmosphere, and organisms. Since your reference book does not include a page for the oxygen cycle, this screen will serve as your reference. Just as you did with the other cycles' diagrams, carefully read through this diagram along with the accompanying captions to get the big picture on the oxygen cycle.

Dam removals nationwide help restore natural river flows. Efforts are underway nationwide to restore natural river patterns by dismantling dams, such as this one on Florida's Kissimmee River. American RIvers American Rivers is a group that works nationwide to restore, protect, and manage the nation's rivers. Visit the group's website, which is listed in the Lesson Resources under Lesson Links, to find out more about the work American Rivers does in restoring waterways to their original state, and also to read more about the dismantling of the dam on the Kissimmee River.

Damming rivers became popular in the early 1900s as a way to generate hydroelectric power, but very little thought was given to how the dams would affect the ecology of the rivers and their tributaries, especially the breeding grounds of wild fish populations. Today, major efforts are underway to dismantle old, inefficient, and harmful dams and to restore the natural river patterns affecting countless ecosystems and the surrounding wildlife, lands, and people.

Photolysis releases oxygen into the atmosphere when radiant light breaks apart the chemical bonds of oxygen-containing molecules.

Dawn breaks across a Kansas prairie, spilling the first specks of light onto the horizon. Without a sound, streaks of salmon pink, tangerine orange, and deep purple paint the sky as if by a few easy strokes. As the minutes pass, and that side of the earth comes in closer contact to the sun, the tangential rays eventually hit directly, resulting in a bright, clear day. The sun's rays do more than light the sky and warm the earth. As their energy beams to the surface at incredible speeds, these rays can splinter chemical compounds such as water molecules or nitrates that fall in their path. In the process, oxygen gas is released into the atmosphere. Find the part of the cycle where this release occurs. Sunrise During photolysis, light energy strikes and breaks up compounds in earth's atmosphere, often releasing oxygen molecules into the air.

During respiration and transpiration, living things give off water. Animals exhale water vapor into the air during respiration. That water vapor enters the atmosphere. Plant cells release water to outside surfaces during transpiration. That moisture evaporates into the atmosphere.

Dawn paints the eastern sky over Yellowstone National Park in northwestern Wyoming with bright reds, pinks, and oranges. The light show is caused by sunlight entering the earth's atmosphere at an angle and being bent, or refracted, partially by water particles suspended in the air. That water comes from many sources, including the respiration Opens in modal popup window and transpiration Opens in modal popup window of plants. The breath of birds and beasts exhaled into the atmosphere contains water vapor. Likewise during transpiration, plants expel water onto the surface of their leaves, which often appears as dew. Moisture from both sources evaporates to contribute to the water content of the atmosphere. Turn to pages 212-213 of your reference book to see the full water cycle.

Nitrogen-fixing bacteria convert nitrogen gas into ammonia and nitrates.

Despite being the majority molecule in the atmosphere, nitrogen gas (N2) cannot be used directly by living things. But, all organisms need nitrogen to live, so how do living things get it? In root nodules of certain plants, bacteria convert nitrogen gas into ammonia and nitrates, chemical substances in which nitrogen is one of the atoms. The plants then use these nitrogen substances. Other organisms eat the plants, and the nitrogen substances move up the food chain from there. The nodule growths on the roots of plants might look like some disease or infection, but this symbiotic relationship between bacteria and a plant gives organisms ready access to the types of nitrogen compounds they need. Refer to the diagram on pages 206-207 of your reference book and locate where nitrogen fixing occurs.

5.14 Water and Nitrogen Cycles Abiotic factors, such as water and nitrogen, recycle through complex mechanisms on earth. Nitrogen and water cycle through the earth, living things, and the atmosphere.

Do you realize that the water you drink was somehow part of something else in this world? Was it once inside the cells of a pig or a fungus? The nitrogen atoms in your DNA—have they only been used in your body? More likely, they were once part of some dinosaur, then maybe an insect, and then maybe a tree before they found their way into you in the recycling process that characterizes many of the abiotic factors of ecosystems.

A Delaware scientist makes plastic products out of newspaper, soybeans, and chicken feathers.

Dr. Richard Wool from the University of Delaware has won awards for his innovative use of environment-friendly materials to manufacture products usually made from petroleum, such as roofing materials and plastics. He even developed a computer circuit board made from chicken feathers. By eliminating the need for harmful substances to manufacture many products, Wool and others like him are helping the environment in many ways. Oil isn't needed to make the products, and when the items do get thrown away, they don't contribute to pollution. This type of technology, called green engineering or sustainable architecture, is one way in which people are addressing new challenges. A number of different labels and seals, such as those shown here, denote environment-friendly products.

Cellular respiration converts glucose, a carbon-based sugar, into carbon dioxide gas.

During each moment of their lives, all organisms must constantly undergo cellular respiration Opens in modal popup window ; therefore, they participate in the carbon cycle. As carbon-based sugars are broken down for the usable energy of ATP, the carbon transfers into molecules of carbon dioxide gas, which are released into the atmosphere with each exhalation. Return to pages 210-211 of your reference book to find where cellular respiration fits into the carbon cycle.

Poor air quality chokes the natural flow of gases in the atmosphere.

Early one morning, a man in Mexico City starts his car. He pulls onto a main road flanked with cement buildings and into the traffic stream of 3 million cars that this city is home to. He must complete all his work and errands today because tomorrow is a "no car day." Considered some of the worst on earth, air pollution suffocates Mexico City and requires policies to allow compounds such as ozone and carbon monoxide clear out of the air. Pollutants suspended in the air cause a wide variety of health problems in both humans and surrounding ecosystems. Today, the younger generation of Mexican schoolchildren is being taught about air pollution and its link to respiratory ailments. The government is working hard to find solutions that will help clean the air. Like Mexico City, other large cities across the globe face the challenge of balancing large populations of people, cars, and factories while combating the harmful effects of air pollution. Pollution in Mexico City Pollution from increased industry and gas-burning vehicles, not clouds, enshroud Mexico City.

Climax vegetation refers to the final species of vegetation to grow in an area undergoing succession.

Eventually, after many years (often decades), the ecosystem once again reaches a point of maturity. The process of succession is complete when a final balance of organisms exists. At this point, no further changes to the balance of organisms should occur. This final state is called the climax community. The species of plants in this community are called the climax vegetation. Ecosystems do have a limit in terms of resources and space with regard to the types and quantity of life that can be supported. The length of time required to reestablish the climax community Opens in modal popup window depends on the ecosystem. In Yellowstone, succession is an ongoing process. The climax community for each ecosystem on the planet is different. Forest Depending on the ecosystem, climax vegetation may require hundreds of years to mature.

Other factors also affect population growth.

Food, water, and predators are not the only limiting factors facing populations of organisms. Nonliving features of the environment, such as weather and disease, also affect how and when populations grow. Many insect populations, for example, grow exponentially during the summer, but their numbers decrease significantly as cold weather sets in. Factors such as climate, temperature, and weather are not dependent on the size of population, as they can affect populations of any size. Turn to page 190-191 of your reference book to read more about patterns of population growth. Missing Metadata Insect populations grow exponentially during warm weather and decrease in size when cold weather sets in.

Pollutants released into water sources spread pervasively through entire ecosystems.

For hundreds of years, families have fished the Huai River basin in east central China. Once the lifeline of village communities, the river basin not only provided fish, but water for drinking and irrigating nearby crops. Today, the human activity that used to surround the river has faded away, as its water now runs full of untreated and toxic factory waste. Huts, often emptied by cancer and other diseases, stand as silent reminders of the people who used to inhabit them. The Chinese government has often encouraged industrialization as a response to the demands of its large population and in the interest of developing the country. Yet, by 2005, only 47 percent of all Chinese rivers were considered drinkable, and more than 100 cities had insufficient sources of water. Half of Chinese lakes and 35 percent of its groundwater were significantly polluted. The water in the Huai River basin was considered dangerous even to touch. Similar situations of water pollution exist worldwide. However, in the first decade of the twenty-first century, the Chinese government initiated a program to improve water quality in China. Man in boat on Huai River Polluted by raw sewage and toxic industrial waste, China's Huai River is even dangerous to touch

Poisoned land is transformed into a community park.

For many years, the 32-acre piece of abandoned land just outside downtown Los Angeles was empty and abandoned. It was nothing more than an unsightly plot of wasted space, full of deteriorating remnants of a past era. But, the land had its own story—in 1871, it was the site of part of an aqueduct to the small community then called the Pueblo de Los Angeles. Before the Civil War, it was a cornfield; most recently, it was a rail yard. Over the years, its soil had become laced with various pollutants, but between 2000 and 2002, the California Department of Toxic Substances Control undertook a cleanup effort to prepare the area for a warehouse complex. After removing 5,200 tons of soil contaminated with petroleum, lead, and arsenic, the land was ready for use. Before the warehouse complex could move forward, however, citizens from more than 25 different groups banded together to work with their local government to transform the acreage into a park. Today, not only is the land providing recreational space to thousands of families, but its trees, grass, and plant life are helping remove carbon dioxide from the air every single day—a service that is particularly important in a smoggy city such as Los Angeles. Cornfield Citizens worked to transform these 32 polluted acres near downtown Los Angeles into a community park.

The water cycle stores and moves water around between land, air, and living things. Cycle Notice how cycle doesn't necessarily mean one singular, circular path. There are many paths and many places that water can cycle through.

Here's how this lesson is going to work. Instead of going through the cycle step by step, you're going to do something a little different. Read pages 212-213 of your reference book. Those pages give the big picture of the entire water cycle—where water goes into the atmosphere and where it comes out. (A simplified version of those pages appears at right.) Once you've got a basic grasp of the nature of the cycle from the book, study the online water cycle, where you will begin viewing specific parts of the cycle. As you concentrate on one part of the cycle, refer again to pages 212-213 of your reference book to find out exactly where you are in the cycle.

Human activities, such as draining a wetland, can cause changes to an ecosystem. Question: If a wetland were drained, how might the ecosystem change? Answer: In general, when an entire wetland is drained or dried up, very few (if any) of the original biotic factors can remain in the area. By some estimates, over half the wetlands that existed 200 years ago in the United States are gone. The Clean Water Act in the 1990s has slowed down the loss of wetlands. People have begun to realize the economic and ecological importance of these unique ecosystems. Aquatic plants are adapted to aquatic living and are unable to survive in drier soils. Draining a wetland destroys the plants at the base of the ecologic pyramid. Fewer plants would mean fewer primary consumers. The number of organisms in each trophic level would change. Ultimately, the aquatic ecosystem would be replaced by a different ecosystem through secondary succession. The hydric soil would change and be replaced with a new type of soil. Many of the original wetland organisms would disappear from the area, and it is possible that local populations of the organisms could go extinct.

Historically, wetlands have been very misunderstood by human populations. Thought to be nothing more than a hindrance to farming, attempts to fill in or drain wetlands were widespread and extensive. Today, the ecological importance of wetlands is well known, and many laws are in place to protect them.To learn more about the different types of wetlands, click here. https://www.epa.gov/wetlands/wetlands-classification-and-types#marshes Wetland plants and animals have many adaptations focused on aquatic living. For example, wetland plants have root systems that have adapted to living underwater. Wetland soil is called hydric soil because it is saturated with water and often builds up a layer of decomposing plant matter.

Change to ecosystems occurs both slowly and quickly. Lions Removing lions from this ecosystem would initially affect other top predators. Hyenas, for example, would no longer have to compete with lions for food. It is possible that hyenas or other top predators would fill the niche left vacant by the lions. Predator populations keep prey species such as zebras healthy by killing sick and unfit individuals. Lions are particularly good at hunting zebras and wildebeests. It is possible that populations of prey species will become unhealthy if lions are removed from the ecosystem. Populations of organisms in an ecosystem are affected by each other. In many cases, populations depend on each other.

How can an ecosystem change? Since an ecosystem is a combination of its biotic and abiotic parts, a change to any part is likely to affect the entire system. For example, an arctic ecosystem would change if large portions of its ice were to melt. A grassland ecosystem would change if its top carnivore disappeared. A marsh ecosystem would change if pollution killed its main plant species. Today, you'll use your expertise to predict what could happen to an ecosystem given a certain situation. Your job will be to predict how the biotic and abiotic factors of the ecosystem would likely change in the given scenario. The examples will be based on two sources of change to ecosystems: climate human activity

A scientist discovers the cause of the hole in earth's ozone layer. More than 20 years later, the hole is beginning to recover. CFCs CFCs were commonly used in products sold in aerosol cans, such as hair spray and cleaning supplies, as well as in refrigerator and air conditioner coolants. Modern versions of those products do not contain CFCs

How would it feel to make a discovery so huge, so important, that it benefited the entire planet? That's what happened more than 20 years ago when Dr. Susan Solomon and a team of other scientists discovered what was damaging the ozone layer. The ozone layer is a part of the atmosphere that protects the earth from the sun's ultraviolet radiation. A huge hole had been growing in it for a number of years. Solomon discovered that it was due largely to the action of manufactured compounds called chlorofluorocarbons Opens in modal popup window , or CFCs, that were being released into the atmosphere from products that contained them. Since Solomon's discovery, the production and use of CFCs have greatly diminished, and the ozone hole is recovering. Production and use of other gases that deplete the ozone layer are diminishing, too.

Removing a species from an ecosystem can cause changes to the system. Original Yellowstone Communities wolves elk cottonwood seedlings Wolves are important consumers in the ecosystem. The relationships between organisms are complex. Wolf populations affect elk populations, and elk populations affect cottonwood seedlings. Damaged Yellowstone Communities wolves elk cottonwood seedlings When humans removed wolves from the ecosystem starting in the 1920s, elk populations began to change. As elk populations increased, the elk ate cottonwood seedlings. Cottonwood populations declined. Wolf Reintroduction wolves elk cottonwood seedlings Today scientists have reintroduced wolves to the ecosystem. Slowly the community of organisms should return to a balanced state. Elk populations are naturally being controlled by wolf populations, and cottonwood populations should recover. Wolf Reintroduction wolves elk cottonwood seedlings Today scientists have reintroduced wolves to the ecosystem. Slowly the community of organisms should return to a balanced state. Elk populations are naturally being controlled by wolf populations, and cottonwood populations should recover. Yellowstone Communities Reestablished wolves elk cottonwood seedlings Ecosystems are complex. When a change occurs in a trophic level, the other topics levels are affected in some way. Biologists work to fully understand an ecosystem's structure and the impact human actions may have on it.

Images of massive snarling teeth, viscious eyes, and dark fur helped propagate a fear and hatred of wolves. Out of misplaced fear, humans hunted wolves down to a few remaining individuals. Under the false hope that all would be well without wolves, the campaign to remove them from the ecosystem was successful. By 1926, the last wolf pack in Yellowstone National Park disappeared. Nearly 100 years later, scientists are reintroducing wolves, hoping they can help save groves of cottonwood trees. Where's the connection? Analyze a Yellowstone food pyramid to find the answer: Yellowstone Food Pyramid

Human activities, such as deforestation, can cause changes to an ecosystem. The Amazon rain forest is one of the largest forests on the planet. Losing forests reduces the amount of oxygen available on the planet. Forest plants produce oxygen in the process of photosynthesis. In addition, forests are frequently cleared by burning. Burning forests consumes oxygen and increases carbon dioxide in the atmosphere.

Is there a human activity that is more destructive than the removal of an entire forest? It almost seems unbelievable, yet since the 1800s, millions of acres of forest around the globe have been cleared so that no trees remain. Changes to those ecosystems seem painfully obvious, such as total or near total destruction and collapse of the food web. Additional abiotic changes also occur to surrounding ecosystems. Erosion destroys top soils, and sediment fills waterways, lakes, and reservoirs. Important biochemical cycles are also affected. In many parts of the world, the biodiversity lost with deforestation is immeasurable. Modern forestry techniques help reduce the impact. The importance of forest ecosystems on the planet continues to be discovered.

Analyzing each environmental challenge in-depth can lead to the discovery of viable solutions. This aerial view of a managed tree farm shows some areas that have been cleared and others with various stages of tree growth. By replacing felled timber with new tree seedlings, forests can be completely renewable resources. Good forest management requires constant monitoring by scientists of wildlife, soil, and other conditions. A botanist at a managed tree farm checks the health of an evergreen to assure a good crop. By selectively harvesting trees, little damage is done to forest soils, growth, and habitat.

It is important to understand that none of the current environmental concerns you'll explore in this lesson are simple issues. For example, look at the case of the timber industry. One extreme includes people who want to clear-cut, or chop down, all trees in a given area, arguing that we need the wood, and that the industry creates jobs and helps the overall economy of the region, state, and nation. The other extreme includes people who wouldn't cut any trees, arguing that trees cleanse the air, combat soil erosion, give habitat to wildlife, and are beautiful to look at. Both sides are correct. How would you resolve the question: To cut or not to cut? What action might you propose? Possible Answer You might suggest something similar to the following: By managing forest resources and establishing tree farms, people can selectively harvest timber without clear-cutting large tracts of trees. This practice allows for the extraction of wood, preservation of lumbering jobs, addition of farm management and conservationist jobs, preservation of animal and plant habitat, and income from both the timber industry and potential tourism.

5.13 Changes in Ecosystems Changes in climate and changes caused by human activity can disrupt and transform entire ecosystems quickly. changes in ecosystems are caused by human activity such as wetland destruction, deforestation, and invasive species or climate change such as long term change in weather patterns and temperatures

It may seem as though the ecosystems you've studied are permanent parts of earth's identity and characteristics. However, that statement is far from the truth. Regardless of how much land they take up or how many organisms inhabit them, entire ecosystems are susceptible to change. Two significant causes of change in ecosystems include climate change and human activity.

Human activities generate large amounts of hazardous waste that pose severe risks to human and environmental health.

It may seem hard to believe, but here in the United States, back when people and companies started using chemicals and making chemical wastes, they didn't really think it was a big deal to throw them away like any other type of trash. Toxic chemicals were simply dumped into landfills or lakes, creating thousands of sites contaminated with hazardous waste. Once the government realized the dangers of such practices, laws were put into place to stop random dumping. The U.S. Environmental Protection Agency (USEPA) manages and oversees hazardous waste disposal throughout the country. In 1980, Superfund, a division of the USEPA, was created to clean up the thousands of hazardous waste sites in the United States. Companies now must dispose of their waste in responsible ways that do not pose health risks to humans, plants, animals, or the environment in general. For more information, select USEPA's Superfund. https://www.epa.gov/superfund Missing Metadata Hazardous, materials are any flammable, corrosive, reactive, or poisonous substances that threaten living things

Many substances used by living things cycle on earth.

It's a hot summer day, and nothing seems more refreshing than a drink of water. You open the water bottle or the drinking fountain tap with the false sense of security that the water has not been used by anyone or anything before. Surprise—whether it is sealed in an expensive bottle with a colorful mountain river scene on the label or poured from your kitchen tap, it's used water. The water molecules you're drinking may have once been part of a nearby stream, a cloud, a plant, or even part of your own body. Maybe they've been part of all those things. They've been used and recycled just like the air molecules you're breathing, and like the carbon and nitrogen in the very structure of all your cells. Without the natural recycling of abiotic Opens in modal popup window materials, life on earth could not be. Your entire body and everything it uses have been used before, and will be used again.

A ban on DDT helps save the bald eagle.

It's early morning in 1952. A crop duster flies low, dumping its load of DDT onto a cornfield. The powerful pesticide, which has the ability to stay active in the environment for up to 90 years, soon saturates many areas of North America. During the 1950s, ornithologists watched in dismay as the bald eagle population plummeted from hundreds of thousands of individuals to a mere 500 pairs by the early 1960s. Eventually, scientists studying eagles discovered that when the birds ingested food and water that contained DDT and other pollutants, they produced eggs with weak shells that cracked before they could hatch. Once the federal government passed laws banning DDT in North America, eagle populations began steadily increasing. Subsequently, the banning of many toxic chemicals has benefited countless other organisms as well. To learn how the elimination of DDT, along with other factors, affected the bald eagle population, select Bald Eagle Pairs Opens in modal popup window . Eagles in flight The harmful effects of DDT once threatened bald eagles with extinction. When the pesticide was banned in the United States, eagle populations rebounded.

Water moves from the atmosphere to the earth in many forms of precipitation. Snow: Depending on temperature, water precipitating from the atmosphere to the earth's surface may take many different forms. Hail: Depending on temperature, water precipitating from the atmosphere to the earth's surface may take many different forms. Rain: Depending on temperature, water precipitating from the atmosphere to the earth's surface may take many different forms.

Late at night in a Midwestern town, snow falls silently, reaching a depth of nearly 12 cm. Flawless white drifts sparkle in the moonlight like diamond dust. Bundled up in doubled socks, boots, and thick gloves, one man gets a head start shoveling out his driveway. After making some headway, he stops to look at the single flakes frozen onto the window of his car. Each flake is an intricate piece of artwork, unbelievably beautiful. He glances around at his street, and smiles with the thought that each flake covering the yards, trees, and homes has its own unique crystal identity. Snow is but one form of precipitating water. Snow, rain, hail, and sleet are all forms of precipitation—water moving from the atmosphere to the surface of the earth.

Earth contains a limited supply of carbon.

Learn how carbon dioxide is absorbed from the atmosphere by plants then passed on as carbon compounds to humans and animals, which then release carbon dioxide back to the atmosphere. Transcript (Video with Audio Description) Screen 1: 00:00:00.00 Description: There is an animated periodic table. The carbon block moves toward the camera and begins to spin. An animated earth rotates in the background. Narrator: The element carbon is essential for plants and animals to survive, but there's a limited supply of carbon here on earth. It's recycled by a series of reactions known as the carbon cycle. 00:00:15.00 Description: There is a video of clouds moving. The earth is still rotating in the background. The video shrinks and an arrow points downward to an image of a leaf. The image of the leaf is enlarged. The next image is a close-up of leaves on a plant and then a cow eating grass. Narrator: The atmosphere contains a small amount of carbon dioxide. C O 2 in the air is constantly being absorbed by plants. They use it for photosynthesis. Carbon dioxide diffuses into the leaves, where it's built up into sugars and other complex carbon compounds. 00:00:38.00 Narrator: When a plant is eaten, the carbon compounds are passed on to the animal. Both plants and animals respire. This process returns carbon to the atmosphere in the form of carbon dioxide. 00:00:54.00 Description: There is an image of clouds, an arrow points from the image of the clouds to the image of a leaf, and an arrow points from the image of the leaf to the image of a cow. There are also arrows from the image of the leaf to the clouds and from the image of the cow to the image of the clouds. The earth is still rotating in the background. There is a time-lapse video of decaying vegetables, including carrots, tomatoes, onions, radishes, cauliflower, artichokes, broccoli, and peppers. Narrator: Another part of the carbon cycle involves decomposition. When living things die, they decompose. The carbon they contain is returned to the soil and the air. Forest fires and the burning of fossil fuels also return carbon to the atmosphere. 00:01:15.00 Description: There is the cycle, which includes the clouds, leaf, and cow. In addition, there is an image of the decaying vegetables. The image of the leaf and the image of the cow have arrows pointing to the image of the decaying vegetables. There is an arrow from the image of the decaying vegetables to the clouds. Images of smokestacks and forest fires have arrows pointing to the image of the clouds. The earth is still rotating in the background.

The carbon from the buried and compressed remains of past organisms is burned as fuel, releasing that carbon back into the atmosphere. Carbon is tied up in hydrocarbons such as coal. Significant amounts of carbon are contained in natural gas and petroleum.

Lines of coal cars rumble past as you wait at a train crossing. The passing black mounds of rocks bear little resemblance to the bodies of the organisms from which they were formed. After death, some organisms become buried and trapped under soil and rock. The carbon in their cells is squashed for enormous periods of time. Eventually, it forms energy-packed substances such as coal, petroleum, and natural gas. Humans burn these materials as fuel because the carbon compounds trapped in the remains contain potential energy that is released on burning. Carbon dioxide gas is also released. Find the part of the cycle where this release occurs.

Carbon and oxygen cycle and recycle through the earth's atmosphere, land, water, and living things.

Many parts of the carbon and oxygen cycles overlap, especially through photosynthesis and cellular respiration. In photosynthesis, carbon dioxide is removed from the atmosphere and converted into sugars. Concurrently, oxygen is released. During cellular respiration, the reverse occurs on a chemical level. Oxygen is taken from the atmosphere and used to generate water and carbon dioxide, which in turn reenters the air. Carbon-based sugars are broken down. Other related parts of the cycle contribute to the complete picture, where not a single atom of earth's resources are wasted.

Nitrogen—most of which is found in the atmosphere—cycles between various reservoirs. Nitrogen Cycle (from picture) The atmosphere is the largest nitrogen reservoir on earth. Fertilizer production and burning fossil fuels release nitrogen into the soil and the atmosphere. Runoff carries ammonia and nitrates into the ocean. Nitrogen-fixing bacteria convert nitrogen gas into compounds that plants and animals can use. Denitrifying bacteria convert those compounds into nitrogen gas that can reenter the atmosphere. Marine organisms rely on nitrogen-fixing bacteria to convert nitrogen gas into nitrogen compounds. Denitrifying bacteria convert those compounds into nitrogen gas that can reenter the atmosphere.

Nitrogen—along with oxygen, carbon, and hydrogen, all of which make up approximately 96 percent of the living matter in your body—is absolutely essential for life. Nitrogen gas (N2) exists in a seemingly inexhaustible supply: It makes up 78 percent of the earth's atmosphere. Unfortunately, nitrogen gas in the atmosphere is not in a form that is usable by living things and, therefore, must be converted to other more usable forms. During the nitrogen cycle, the chemical forms of nitrogen change. Explore the simplified version of the nitrogen cycle diagram and then go to pages 206-207 of your reference book for a more detailed explanation of the nitrogen cycle. When you're ready, you'll do the same thing that you did with the water cycle—pick a few points in the cycle and study them in more detail.

Scientists consider carbon dioxide, methane, nitrous oxide, and a few other compounds to be the main causes of the increase in global temperatures. The pie chart shows carbon dioxide (78%), fluorocarbons (5%), Nitrous Oxide (6%), and Methane (13%)

One big question about global warming is: Are atmospheric temperatures rising naturally or because of some human activities? Scientists can help answer this question by determining what the excess atmospheric gases are and where they come from. Through careful study, scientists can provide factual information to help us decide how to act. Taking good data and reporting it objectively have been—and will continue to be—hallmarks of good science. Check out this pie chart, which includes data on the major greenhouse gas emissions in the atmosphere.

Developments in modern society have led to serious challenges to the natural environment. From Pictures As this oil-soaked penguin attests, massive petroleum spills seriously threaten the health of plants and animals. Many rivers and streams are polluted with garbage that destroys wildlife and the beauty of the landscape. The vehicles of commuters driving in and out of cities such as Boston emit tons of pollutants into the atmosphere. The 1979 partial meltdown at Pennsylvania's Three Mile Island Nuclear Generating Station led to major changes in nuclear power management. Every year, tens of thousands of acres of forest are clear-cut for timber or burned to create farm or grazing land. Traditionally, suburban housing developments have encroached on and destroyed large tracks of rural woodlands.

Recent scientific studies have determined that parts of earth are in poor shape. We've tried to make our lives better by building homes, machines, factories, cities, and dams. In the process, however, we have often seriously wounded the health of the natural environment—the very environment on which we depend. The challenge facing people around the globe is how to sustain the continued development of human society without destroying that environment and its natural resources, health, and space. Today, more and more people are seeking solutions to environmental challenges.

Water's Cycling Forms

Review how water cycles through four stages, changing from one form to another: evaporation to condensation to precipitation, and finally to collection. Transcript (Video with Audio Description) Screen 1: 00:00:00.00 Description: There is a series of images: A lake, a river, rain, snow. 00:00:06.00 Female Narrator: Where does water come from? Rain? Snow? The sea? But where does rain and snow come from? 00:00:18.00 Description: There is a series of images: Ice melting, then water melting. 00:00:23.00 Female Narrator: There is a constant amount of water on the earth, and it can be in the form of a solid, liquid, or gas. The water cycle describes how water moves and changes from one form to another. It's made up of four steps. 00:00:43.00 Description: There is an animation of a mountain, the beach, the ocean, and the sun. Water rises from the ocean into clouds, the clouds move up over the mountain, and rain falls. This forms a stream of water down the mountain to the ocean. 00:00:59.00 Female Narrator: First, evaporation. When the sun heats up water in rivers or lakes or the sea, it becomes vapor. The water vapor rises and goes into the air. Water vapor is also created by plants through what's called transpiration, water given off from plant leaves, which then evaporates into the air. Water vapor in the air gets cold and changes back into liquid, forming clouds. This is called condensation. 00:01:36.00 Description: Two arrows move upward from water to the air indicating evaporation. The bottom parts of the arrows are pink and the top is blue. Clouds form above the arrows. There are water drops on leaves. Water vapor rises from a microscopic hole in the plant leaf. There is a video of moving clouds. Steaming water is poured into a 2-liter plastic bottle. The top part of the bottle is cut off, inverted, filled with ice, and placed on top of the bottom part of the bottle. The air on the inside of the apparatus at the top becomes cloudy. 00:02:13.00 Female Narrator: The same thing happens when warm water is poured into a container and ice is introduced. Water vapor coming into contact with the ice is cold, and condenses, forming clouds. When so much water has condensed that the air or the clouds cannot hold any more, then we get precipitation. Water falls back to the earth in the form of rain, hail, sleet, or snow. 00:02:44.00 Description: There is an animation of a cloud with rain. There is a series of images: Rivers, waterfalls, and rain on green plant leaves. 00:02:54.00 Female Narrator: The final part of the cycle is collection. Some of the water will fill up rivers and lakes, and some of it will soak into the earth and become part of the groundwater system. Then the cycle starts all over again.

Politicians consider several perspectives when making decisions, with the scientific perspective being only one of them.

Scientists can present information and answers that inform debate about many issues. Scientific data and suggestions did inform the development of the Kyoto Protocol. Objective and honest science is very important in these situations, but many other factors—economic vitality, health, trade, and even public relations between nations—are also involved. In 2001, before the enactment date of the Kyoto Protocol, the U.S. government withdrew its participation in the agreement, citing concerns about the protocol's potential negative impact on the U.S. economy and a dislike for the exemption of some specific countries. To withdraw was a political decision based on consideration of the scientific evidence and a broad spectrum of other social and economic issues. Even armed with good scientific information, decisions about the environment are often very difficult to make. Congressional hearing The U.S. Congress relies on solid scientific data to make informed decisions about environmental affairs.

Effects of increased global temperatures have been documented scientifically. The ranges of the northern cardinal and other animal and plant species are expanding northward due, in part, to global warming. As global temperatures rise, glaciers around the world are slowing their growth and movements, and in many cases are receding. With increased temperatures worldwide, melting glaciers and receding snow and ice caps contribute to rises in sea level.

Scientists continue to supply information to decision makers. Some recent scientific studies have shown the following: 10 percent decrease in snow cover worldwide significant retreat of glaciers rise in sea level of 0.1-0.2 rn since 1900 habitat change for many species Remember, one hallmark of scientific methods is that the research is published along with the research methods. This step allows other people—scientists and nonscientists alike—to read the studies, reconstruct the research, and evaluate the accuracy of the science. In any debate as serious as the one concerning possible climate change, scientists must continue to provide information to leaders and citizens.

Organisms change as the environment continues to change.

Secondary succession can occur much more quickly than primary succession. In secondary succession, some plants are able to return quickly since the topsoil is still present. Grasses, flowers, and mosses move in first. In the case of the Yellowstone fire, one of the earliest plants to arrive was the beautiful flowering plant fireweed (Epilobium angustifolium). Eventually, low-growing plants like fireweed are overtaken by taller bushes. The bushes cast the plants into a permanent shade. The taller bushes outcompete the low-growing plants for sunlight. Land after a fire Fireweed was one of the first plants to grow back after the Yellowstone forest fire. Fireweed can be seen in the foreground.

The introduction of nonnative, invasive species can lead to secondary succession. Pictures: These yellow crazy ants (Anoplolepis gracilipes) are attacking a bait strip. The ants destroyed the native land crab population. Giant reeds (Arundo donax) outcompete the native plant species. The nonnative reeds are changing entire habitats. Feral domestic goats (Capra hircus) have taken over much of the island, eating nearly every plant in sight.

Secondary succession is the replacement of living things in a specific area, which frequently occurs through the introduction of a invasive (nonnative) species. Invasive species cause unnatural forms of succession in varying levels of severity. Invasive species can have dramatic effects in an ecosystem—from changing the population sizes of native species to altering the entire structure of plant life. Christmas Island is located in the Indian Ocean off the northern coast of Australia. The island's fragile climax community has been under attack by foreign invaders. The gallery at right presents three examples of invasive species on the island. To learn more about Christmas Island, click here. http://www.parksaustralia.gov.au/christmas/index.html

Human activities, such as introducing excessive nutrients, can cause changes to an ecosystem. Algae are the primary producers in many aquatic ecosystems. Algae flourish with the help of added nutrients. The algal bloom outcompetes the aquatic plants and other organisms in the lake. The number of organisms at the producer level of the ecosystem is greatly exaggerated. In this case, both the biotic and abiotic factors in the lake are changed by the algal bloom. In extreme cases, the water can even become toxic to many native species.

The Salton Sea, a large lake in southeastern California, is a classic example of how excess nutrients can affect aquatic ecosystems. Some forms of pollution come hidden under the term nutrient pollutants because they are compounds that usually feed the growth of plants on land. Two common nutrient pollutants are nitrogen and phosphorus. Compounds containing these two elements frequently are used as lawn and crop fertilizers. Ninety percent of the water flowing into the Salton Sea is irrigation runoff from agricultural valleys. The area receives very little water in the form of rain, and the water in the lake is extremely salty. When the nutrients enter into an aquatic ecosystem, such as a freshwater lake, the effect on the plant life is the same as to the plants on land, but massively exaggerated. Plant growth also includes algae, which in great numbers can severely impact an ecosystem.

Water and nitrogen cycle between the atmosphere, the earth, and living things.

The balance of necessary substances, such as water and nitrogen, are maintained through complex cycling systems. The water cycle continuously moves and stores water between the atmosphere, the earth, and living things. Water enters the atmosphere through evaporation, respiration, and transpiration. It comes back to the earth in the form of precipitation. Nitrogen in the atmosphere cannot be used directly by living things. Certain nitrogen-fixing bacteria chemically convert nitrogen gas into forms of nitrogen that plants and other living things can use. Both the water cycle and the nitrogen cycle have more than one pathway through which these substances can travel.

Cellular respiration removes oxygen from the atmosphere, combining it with hydrogen to form water.

The diversity of structures through which organisms respire is quite astounding in and of itself. You might think that everything with a mouth uses it for breathing, but that isn't always the case. Insects breathe through small holes in their abdomen called spiracles. Frogs hibernating underground exchange gases through their skin. Birds usually breathe with their mouth closed, taking air in through holes in their face called nares. Whales breathe out of the top of their head from a blowhole. Regardless of the equipment, cellular respiration in living things is crucial to the oxygen cycle. It removes oxygen from the atmosphere, ultimately bonding it into molecules of water. Find the part of the cycle where this bonding occurs.

Mercury, a type of hazardous material, poses a serious threat to health, especially in children. Fish Unfit to Eat Officials in 45 states have issued advisories against eating local fish from some 12 million acres of lakes and 473,000 river miles because of mercury pollution. The concentration of mercury increases up the food chain. Microscopic plants and animals absorb mercury from the water in which they live. Crayfish eat plankton and ingest all the mercury that they contain. By eating lots of crayfish, trout accumulate large amounts of mercury in their system. By eating fish, we can ingest high concentrations of mercury.

The element mercury is one example of hazardous material. At high enough levels, it is known to cause developmental abnormalities in babies, and is often related to brain function problems in adults. In Illinois, 100 percent of the waterways are polluted with mercury, most of which comes from burning coal in plants and factories. Mercury passes into the food chain easily and reaches high levels in higher-ordered organisms, such as fish and birds. Mercury is retained in most living things rather than being consumed, broken down, or excreted. Therefore, if a big fish eats 10 smaller mercury-containing fish, the larger fish will have the mercury of all 10 smaller fish in its system. If a person eats two such larger fish, that person ingests even higher levels of mercury.

Current environmental problems can be attributed to various causes. City Lights from spaceA map of the world at night with city lights, contrasting an overall very dark image. Areas with high concentrations of light are in the eastern half of the United States, most of Europe, the top western tip and eastern coastal region of South America, the northern coastal area of Africa, India, the eastern half of China, Japan and the eastern coastal region of Australia. One way scientists assess growing urban development is by examining the city lights from space. On this world map, lighter areas indicate greater urbanization and relatively denser population concentrations. Uncontrolled human population growth usually has negative impacts on ecosystems. Deforestation, urban development, and grazing reduce vegetation that is important for purifying air and water, minimizing erosion, and providing habitat for species. Pollution from burning fossil fuels and heavy agricultural use of chemicals leads to an increase in greenhouse gases and climate change; depletion of soil nutrients; and disruption of the nitrogen, water, and other abiotic cycles.

The rapid increase in industrialization since the mid-1700s has contributed to environmental strife in a wide variety of ways, including excessive use of nonrenewable resources destructive practices in acquiring materials inadequate policies in waste disposal lack of planning for long-term effects Other issues, such as the massive increase and spread of the human population, also play major roles. With so many more people to house, feed, and employ, the burden on earth's resources is vastly greater than it was when people began to industrialize the world. Human Population...Since major industrialization began in the late eighteenth century, the human population has exploded from an estimated 600 million to more than 6 billion.

Steadily increasing temperatures on earth are caused by high levels of carbon and other emissions.

The science behind global climate change—also known as global warming—is based on the principles of scientific methods. Scientists provide data about greenhouse gas emissions and other environmental issues. The data is subjected to review and reexamination by other scientists. In addition, scientific data is used by government officials, industry leaders, and private citizens to help make informed decisions.

With proper planning, people can reverse the effects of pollution.

The stories you just read show that when people join together, they can make the world a better place. Making things better, however, requires a knowledge of biology—earth's living things and how they fit into their abiotic environment. Additionally, paying attention to scientific methods is key. Science can aid us in making decisions about our world as we face future challenges.

A local group cleans up a contaminated pond community in Montana.

The storm clouds eventually reached the breaking point, unleashing a downpour over the Mill-Willow Bypass near the Clark Fork River in Montana. The water level rose high enough to push the river into adjoining tracts of land—land polluted with arsenic, cadmium, copper, lead, and zinc from nearby mine waste. By morning, a once-thriving 250-acre pond community was transformed into a toxic wash filled with the floating carcasses of 5,000 fish. Inspired to make a change, a local group joined with the U.S. Environmental Protection Agency (USEPA) and spent 5 years cleaning up the area. Today, the Mill-Willow Bypass is a popular trout-fishing spot and supports more than 140 species of birds, including bald eagles. Missing Metadata Groups are working to clean up waste from mining, which has polluted many regions of the American West.

http://k12.http.internapcdn.net/k12_vitalstream_com/CURRICULUM/1349705/CURRENT_RELEASE/HS_BIO_World_Population.html

The world's population could reach 10 billion by the end of the twenty-first century due to better living conditions and healthcare.

Each environmental concern comes with complex issues with many perspectives. Positive solutions must be sought.

This lesson has only scratched the surface when it comes to the environmental challenges that we face. Each issue concerning the environment must be addressed from multiple sides and take into consideration many perspectives. Science plays a critical role in providing factual and objective information for all these situations. When interests on opposing sides are pulling in their own directions, solid scientific information can make clear to lawmakers and citizens how critical the problem is and can become, and what is necessary to do to protect the health of people and ecosystems.

Carbon is one of the most important elements on earth with regard to living things. Carbon Cycle from class: Plants and animals release carbon dioxide as part of cellular respiration. Plants remove carbon dioxide from the atmosphere. The cells of living things on the earth's surface contain carbon. The burning of fossil fuels releases carbon dioxide. When dead organisms break down, carbon dioxide is released into the atmosphere. The cells of sea life contain carbon. Decomposing sea life releases carbon dioxide. Carbon dioxide dissolved in water can disperse into the atmosphere. Also, carbon dioxide can dissolve in surface water.

This lesson will be similar in structure and form to the previous lesson as you investigate two more very important cycles—those of carbon and oxygen. Remember that carbon is one of the key elements for all living things on earth. Like other abiotic factors, carbon cycles and recycles between earth's soil, atmosphere, and organisms. First turn to pages 210-211 of your reference book and read about the carbon cycle. It might be helpful to make a list so that you can keep track of the various ways carbon dioxide enters the atmosphere because there are so many. As you read, keep in mind that carbon is found virtually everywhere on earth. Then study the online diagram:

Earth Friendly Plastic (shows strawberry container)

This strawberry container is not made from petroleum products, as most plastics are. It is made from a clear resin called polyactide (PLA), which is derived from the carbon. natural sugars, and starches found in corn. Not only is PLA biodegradable, but its manufacturing process contributes far less to greenhouses gases and other pollution than the process required to make traditional plastic products.

5.20 Environmental Challenges The expansion and industrialization of human society often trigger environmental problems that require solutions

Throughout history, humans have been tirelessly attempting to improve our standard of living, hoping to make our daily life more convenient, healthy, and even exciting. Since the beginning of industrialization in the 1700s, this quest has left, and continues to create, environmental problems in its wake. Government and corporate leaders, scientists, and everyday citizens are working to find solutions to these problems.

Droughts cause changes to ecosystems. Indicator Species In the Mojave food web presented here, the top predators are in the most danger because there are not many top consumers to begin with. Think about an energy pyramid: There is not much energy arriving at the top trophic levels. Top predators often are highly specialized organisms with very specific ecosystem needs. These species can act as indicators regarding the health of the rest of the ecosystem. If this drought had continued, what possible impacts would this have had on the ecosystem? If the producers are unable to survive, all the consumer trophic levels would be affected.

Using your knowledge of ecosystems, try to predict how a food web might be affected in response to a severe drought. From 1987 to 1991, the Mojave Desert experienced an extended period of drought. During that time, scientists observed that large percentages of the plant life did not survive. For example, of the creosote bushes (Larrea tridentate) present before the drought, only 58 percent of the plants were alive at the end of the drought. Using this model of a Mojave food web, study the trophic levels and answer the question.

Two African leaders help return wildlife to Namibia.

Uukwaluudhi and Salambala, large areas in Namibia Opens in modal popup window in southern Africa, lost their major wildlife species when war took over the land. As people were forced to spread into the wilderness, entire populations of elephant, antelope, wildebeest, and lion scattered to other places. In doing so, the food webs in Namibia collapsed, and the ecosystems there were destabilized. King Hosea Taapopi of Uukwaluudhi and Chief Moraliswani II of Salambala dreamed of returning native animals to their land. With funding from several international groups and support from the community, their dream came true. In 1999, herds of zebra were returned to Salambala for the first time since 1975. Today, they are joined by elephants, lions, and antelopes. With the return of the wildlife, tourism in the region also returned, boosting the local economy and providing more jobs for residents.

5.04 Ecosystem Stability Ecosystem stability is the ability of an ecosystem to resist significant changes. ecosystems are stable but can become unstable if abiotic and biotic conditions change.

Wave after wave in never-ending succession crashes onshore along Cannon Beach in Oregon. Despite the constant disruption by the ocean waves, the shoreline ecosystem remains intact. The tide pools there are very stable communities of organisms such as sea stars, snails, and barnacles.

Agricultural pollutants generate multiple environmental concerns.

What could be more serene than driving past acres of green farmland? Yet, as idyllic as it may seem, the farming industry has often been directly responsible for many environmental problems. To help protect crops and animals, enormous amounts of toxic chemicals, pesticides, herbicides, antibiotics, and nitrogenous fertilizers are poured, sprayed, and scattered onto millions of acres of land. Many of these chemicals have been proven harmful to both people and animals, in addition to polluting the water. Yet, some farmers claim that without these products they would not be able to afford to produce enough food for us to live on. Dead fish on shore Excess agricultural chemicals can pollute waterways, which poison fish outright or suffocate them by aiding algal growth that takes oxygen out of the water.

5.21 Global Temperatures There is evidence that we are experiencing a period of rising temperatures, and a major debate revolves around the causes of the global-warming phenomenon. scientific methods provide objective data on climate changes for public debate and policy decisions.

What role can science play in the increasingly important debate concerning what to do about global warming? By supplying objective data gathered through the sound application of scientific methods, scientists can help us better understand the nature of global warming and make better decisions about how to react to it.

Runoff from the water cycle carries nitrogen compounds into the oceans. Review Go back to your reference book and review the nitrogen cycle and water cycle diagrams on pages 206-207 and 212-213, respectively. Evaporation Light energy from the sun changes liquid water into water vapor, which enters the atmosphere. Condensation Water vapor collects in the atmosphere, where it forms clouds or fog. Precipitation Water falls from the sky as rain, sleet, hail, or snow. Runoff Water that cannot soak into the soil or into rocks will run off, carrying nitrogen compounds from earth's surface with it. Collection Water, along with the nitrogen compounds it is carrying, collects in lakes, ponds, oceans, and other low spots on earth. Seepage The water that trickles down through the soil will carry nitrogen compounds to collect underground or flow into lakes and oceans.

When colonial Americans cut down forests to make farms, they unknowingly began a process that depleted the soil of the nutrients it contained. Nitrogen compounds used by living things dissolve easily in water. If the nitrogen compounds in soil have not yet made it into a life-form and water comes along, the nitrogen compounds get washed away, often eventually into an ocean. Trees and forest plants act as barriers to runoff, slowing and reducing water flow and, in turn, protecting the soil. When those trees and plants are removed, the soil and its nutrients are easily washed away

Radioactive waste poses a unique problem because of its extreme longevity. 3,000 Tons The United States produces about 3,000 tons of radioactive nuclear waste each year.

When scientists and engineers first supported nuclear energy, the issue of waste disposal was not a big concern. People believed it could be disposed of by burial until it was no longer dangerous. But, it takes an extremely long time for radioactive waste to break down and become inert, or safe; until then, it is highly dangerous to the cells of living things. Scientists now think it will take approximately 3 million years for all nuclear waste on earth produced since 1983 to become safe. Scientists and policy makers are asking the following questions: How can we contain such waste for so long without leaking? Are humans capable of constructing a truly safe holding place? What about the new nuclear waste being generated each day? Storing radioactive waste in Yucca Mountain region Controversy surrounds how and where to best safely store radioactive wastes from medical facilities, power plants, and other sources.

Water evaporates from oceans and other water sources into the atmosphere. The sun rises high above the earth. The sun's rays warm the earth. The warming rays cause earth's water to evaporate. Water molecules condense around particles in the atmosphere. Condensation stores water in the form of clouds.

Whether experienced as a gurgling brook, a raging river rapid, a serene mountain lake, a friendly fountain, a slow-moving glacier, or the gently rising and falling pulse of vast ocean waves, water can evoke the full gamut of human emotions—tranquility, fear, inspiration, joy, or awe. Wherever it's found, in whatever state, the surface expanses of the world's water are warmed by beams of sunlight, causing evaporation Opens in modal popup window . Water molecules then condense Opens in modal popup window into water droplets by clinging to dust or other small particles suspended in the atmosphere, forming clouds. Locate this action on the water cycle diagram on pages 212-213 of your reference book.

Scientists point to increased greenhouse gas emissions from human activities as the major cause of the temperature increase.

Whether naturally produced or released from burning fossil fuels or wood, gaseous compounds enter the atmosphere. There they trap and reflect back to earth sunlight that bounced off the earth's surface, causing the greenhouse effect Opens in modal popup window . Without the greenhouse effect, earth would be cold and inhospitable. A number of scientific studies, however, indicate that carbon dioxide and other gases—sometimes called greenhouse gases—are increasing in earth's atmosphere. As a result, more-than-normal amounts of heat are trapped, causing a rise in atmospheric temperatures that could be dangerous. These facts are the basis for current discussions about what has been labeled global warming. Science can play a role in informing and educating those people—on both sides of the question—who are concerned about this issue.

Changes in temperature cause changes to ecosystems. As the Ice Age ended in Illinois, the mammoths may have found the new environment inhospitable. Warmer temperatures would have made it very difficult for the mammoths to maintain their body temperature.The mammoths retreated north, following the colder temperature, and eventually went extinct as the habitat around them changed. An abrupt change in an ecosystem can be difficult for a well-adapted organism to handle.The organism suddenly finds itself adapted to the wrong ecosystem.

White spruce, a type of conifer, inhabits ecosystems with colder climates. Today, it commonly grows in the northeastern United States and throughout much of Canada. However, about 16,000 years ago, it was abundant throughout Illinois and Missouri, where it is now rare or doesn't exist. Why are there few or no white spruces in Illinois and Missouri today? About 16,000 years ago, the North American climate started warming after a long period called an Ice Age. White spruces, which need colder temperatures, must have found it too hot to live, so they were outcompeted by other trees. A long-term shift in temperature causes a major change in an ecosystem. That change affects living things. For example, woolly mammoths once roamed Illinois; their thick fur and massive bodies were advantageous during the Ice Age. How do you think they took to the warming temperatures? To see how changing temperatures 16,000 years ago affected the plants and animals of the U.S. Midwest, click here. http://exhibits.museum.state.il.us/exhibits/larson/picea.html

Despite massive environmental problems, people can and have made a difference.

You have covered a lot of ground in this course's lessons and gained many different perspectives on life and living things. How can you apply some of what you've learned in your daily life? As earth's population grows, the planet is undergoing many environmental changes, some of which are damaging ecosystems and communities of organisms. Many people around the world have already begun to work together to solve some of those environmental problems such as cleaning up pollution Opens in modal popup window , and they have succeeded in many instances. There are many newsworthy examples of people who made a difference. Check out the stories that follow. Earth People working together are making the planet a better place for all living things.

Photosynthesis releases oxygen into the atmosphere.

You now know the routine of food chains—big things eat smaller things that eat even smaller things and so on. Well, in the ocean, even smaller things play another role aside from being something else's lunch. Phytoplankton by the millions grow in the world's oceans. However, thanks to the presence of chlorophyll in their cells, they can undergo photosynthesis to release massive amounts of oxygen into the water and atmosphere. Collectively, they release so much oxygen that phytoplankton are a major factor in the global climate. During photosynthesis, oxygen is released as carbon-based sugars are produced. Find the part of the cycle where this release occurs.

Different ecosystems are characterized by different biotic and abiotic factors.

You would not expect to see a penguin living in a rain forest. You also would not expect to see a tiger living in the Arctic or a shark living in the desert. A stand of trees in a rain forest, an area of the tundra in the Arctic, and a ravine in a desert are distinct ecosystems characterized by local conditions of water and light (abiotic factors) and specific communities of organisms (biotic factors). To a large extent, abiotic factors play a significant role in shaping ecosystems and determining the kinds of organisms that live there. Explore some organisms that are adapted to the abiotic features of their ecosystem.

5.15 Carbon and Oxygen Cycles Like water and nitrogen, carbon and oxygen also cycle through the earth, the atmosphere, and living things.

You'd be hard pressed to find a place on earth where there isn't carbon. Often, oxygen and carbon are bonded together in different ways—carbon dioxide (CO2) and glucose (C6H12O6) are two common examples. In this lesson, you'll learn about the carbon and oxygen cycles and see how they work.

lichen

a life form which grows as crusty patches on soil, rocks, and trees; lichen forms when an alga and a fungus grow together

Trophic Level

a producing or feeding level in a food chain

pioneer species

a species that is among the first to colonize bare land

keystone species

a species whose impact on or importance to an ecosystem is greater than its numbers would indicate

pollution

the presence of harmful materials in the environment

consumer

an organism that eats other organisms

A community of organisms and its abiotic factors make up an ecosystem.

A Gila monster in a scorching desert, polar bears in the snowy Arctic, otters splashing in a muddy creek, and bluebonnets soaking up the sun on a Texas prairie—each organism is interacting in some way with the abiotic factors of its environment. Abiotic factors such as temperature, sunlight, and water determine the types of plants, animals, and other organisms that can live in a specific place. In this way, abiotic factors have an important role in determining the composition of species that live in different areas. Taken together, biotic Opens in modal popup window and abiotic Opens in modal popup window factors make up an ecosystem Opens in modal popup window . Missing Metadata Heat and scant rainfall are two abiotic factors of this Gila monster's desert ecosystem.

Members of a community interact with each other. Lichen Lichen is a hybrid organism made up of fungi and algae.

A caribou herd stops to feed on tender lichen Opens in modal popup window in the Canadian tundra. It is late summer, and the caribou's predators are not only the wolves that live in the area, but also the thousands of blood-sucking black flies and mosquitoes that swarm above the ponds and lakes. Flocks of waterfowl slurp up insect larvae from the water, which is finally free of ice for a few brief weeks. Like almost all members of this community, they need to feed and rear their young in the short warm season. Populations within a community interact directly and indirectly with each other in various ways.

An ecosystem includes the community and the environment in which those populations live. The cupped leaves of a bromeliad plant form a tiny ecosystem with living and nonliving elements.

A certain type of bromeliad that grows in a Bolivian rain forest puts out a brilliant red blossom. This so-called air plant absorbs the nutrients it needs directly from the atmosphere. It also uses the sun's rays, along with the carbon dioxide and water in its environment, to make food during photosynthesis. The bromeliad's stiff, cupped leaves hold a pool of rainwater. Insect larvae and even tadpoles can live in that secluded watery hideout, which is actually a tiny ecosystem in itself. The individuals in an ecosystem depend on abiotic factors just as much as they depend on the biotic factors. If, for example, the water in the bromeliad cup dried up, then the tiny ecosystem would cease to exist. The bromeliad plant has large thick, waxy leaves that form a bowl shape in the centre for catching water. The center where the water is caught is a place where living and non-living elements can create an ecosystem. The cupped leaves of a bromeliad plant form a tiny ecosystem with living and nonliving elements.

5.02 All the populations in one area make up a community. The living community combined with the nonliving environment make up an ecosystem. Populations make up a community. The community and environment make up the ecosystem, which is made up of biotic factors and abiotic factors.

A gray fox bounds after a field mouse scurrying toward a snow bank, while a red-tailed hawk swoops toward the mouse at the same time. All three organisms breathe the same air, drink the same water, and inhabit the same area of land. Communities of living things interact with the environment, and together they define an ecosystem.

In an ecosystem model, an arrow indicates energy flowing from one organism to the next.

A mother hare digs into the freshly fallen snow. Nuzzling its nose to the ground, it reveals some frozen arctic sedge, a hearty, grasslike plant. Sedge provides the fuel that the hare needs to stay alive in the bitterly cold landscape. Earlier in the spring, the sedge utilized the sun's energy to produce the food it now stores in its stems. In the Arctic ecosystem, the sedge is a producer and the hare is a consumer. Let's explore how a scientists would diagram relationships within the Arctic ecosystem. When energy—in the form of food (or sun's energy)—moves from one organism to another organism, it is symbolized in the diagram with an arrow. The arrow points in the direction of the energy flow.

Individuals make up populations.

A pack of wolves, a parliament of owls, a colony of penguins—people have come up with many different ways of referring to groups of individuals. In ecology, a group of individuals of the same species is called a population. A population Opens in modal popup window is a group of the same species of individuals living in the same area and interacting with each other in some way. Populations of the same species may be separated by geography. For example, the penguins living in one area of Antarctica make up a different population from the penguins living in another area of Antarctica. Missing Metadata A population is a group of the same species of individuals living and interacting in the same area.

A single pathway of arrows represents a food chain.

A shadow from an overhead rough-legged hawk sends the hare bounding for cover. The hare holds statue still. It waits for the hawk to fly far enough out of site to make a dash for its burrow. Nearly there, the hawk reappears suddenly swooping in, its piercing eyes focused on the hare. To create a food chain Opens in modal popup window , put the organisms in order in terms of energy flow. Each arrow in the food chain represents the energy flow from one trophic level Opens in modal popup window to the next. Check out the diagram on-screen, and then go to page 202 of your reference book to learn more about food chains.

Every living thing is part of the biosphere.

All life on earth is organized into levels beginning at the level of the individual. Individual organisms make up populations, and populations grow in several different ways. Exponential growth occurs when population numbers are not restricted in any way. While populations can grow exponentially for a while, eventually their growth is limited by factors such as the availability of resources.

You can identify parts of a community. Pond Community Underwater plants Some plants, such as Canadian pondweed and quillwort, live completely underwater. Because ponds are shallow, many underwater plants can grow in the fertile silt of the pond bottom and still receive enough sunlight to thrive. Cattails and reeds Growing near a pond's edge, cattails and reeds send their roots into the muddy bottom and stick their leaves up above the water's surface. Waterfowl often build nests in the thick stands they form. Dragonflies Dragonflies are members of the order Odonta, which includes only one other insect—the damselfly. Dragonflies are highly skilled predators. Their huge eyes enable them to detect the slightest movement. They catch flying insects in mid-air, seizing them with their strong legs. Snails Pond snails wander slowly up and down the stalks of underwater plants and the underside of lily pads. Most snails are herbivores and feed on plant parts. Their predators include fish, large beetles, and caterpillars. Like frogs, snails are sensitive to changes in the environment, and many species have gone extinct in recent years. Snapping turtles One of the largest turtles in North America, snapping turtles are distinguished by the sawtooth structure on top of their shell. Unlike most other turtles, they cannot retreat into their shell. Snapping turtles eat pond animals as well as plants, algae, and even birds when they can catch them. Fish One typical pond fish is the minnow—the common name for members of family Cyprinidae, the largest family of freshwater fish in North America. Minnows are extremely adaptable and thrive in many different habitats. A single small pond might be home to half a dozen minnow species. Ponds also support stickleback, another small fish that can live in a variety of watery environments. Mint Mink are members of the largest family in the order Carnivora—Mustelidae, which includes weasels, skunks, otters, badgers, and other similar small mammals. Mink are about the size of a house cat, and they eat just about any animal they can find, including fish, mice, frogs, snakes, birds, and bird eggs. Duckweed Duckweed is an aquatic plant that is not anchored in soil. The plant floats on the water's surface, and its roots dangle down in the water, balancing the plant and soaking up nutrients. A large population of duckweed can create a shimmering green carpet across the surface of a small pond. Water lillies With their roots sunk into the pond bottom, water lilies send their leaves up to the surface. The large, rounded leaves of water lilies unroll when they reach the top of the water. The leaves are smooth and waxy, so they float. The flowers also float, and when it rains, they close up to keep from sinking. Water striders Water striders are insects that live in lakes, ponds, and slow-moving rivers and streams. They glide over the surface of the water, staying suspended with the help of hairs that cover the underside of their body. Water striders eat any tiny creature they can catch, including insects, tadpoles, and small fish. Backswimmers These insects got their name because they swim on their back. Backswimmers—also called water boatmen—have a pointed beak instead of jaws. They swim underwater and use their beak to stab at tiny surface organisms from below. Frogs Frogs are amphibians. Young frogs, called tadpoles, breathe through gills, but as they mature, they lose their gills and develop lungs. Frogs eat insects and small invertebrates, and their predators include wading birds, large fish, and carnivorous mammals. Frogs are extremely sensitive to changes in the environment, and their populations have declined significantly since the 1950s, with some species going extinct. Water shrews Tiny water shrews subsist mainly on aquatic insects and small invertebrates such as worms and slugs. When shrews dive underwater in search of food, air bubbles trapped in their fur help them rise back quickly to the surface. Their predators include mink, weasels, and even large fish such as bass and trout. Wading birds Wading birds such as herons, cranes, egrets, and bitterns live in wetland habitats. Moving silently through the shallows on stalk-like legs, they catch unsuspecting fish with their long bill. Many wading birds also eat mice, frogs, and toads. Some birds build their nests in groups in trees near the water; others build in reeds along the bank. Dragonfly nymphs Dragonflies spend the early part of their lives underwater in the nymph stage. They breathe by taking in water and passing it through internal gills. The act of expelling the water also helps them move through the water—jet propulsion on a tiny scale. Dragonfly nymphs eat insects and insect larvae, and sometimes even small fish.

Along the edge of a pond, tall cattails sink their roots in the rich silt of the pond floor, creating an underwater forest for a variety of fish to live out their lives as both predator and prey. A frog croaks from its perch on a lily pad, and water striders glide across the surface of the pond. A wading bird plucks fish from the water with its long bill, and a snapping turtle forages along the bank. All of the organisms living in and around this pond make up the pond community. Explore the roles of different organisms in a pond community. Communities Change Communities can and do change over time. New organisms can migrate into an area and old ones can die off or leave.

The smallest unit of a biosphere is the individual.

An individual is the smallest level of ecological organization. Whether an organism is as large as an elephant or as small as a single bacterium, all levels of ecological organization begin with individual organisms. Missing Metadata An individual, such as an individual penguin, is the smallest level of ecological organization.

Primary succession brings the first new organisms to an area devoid of life. New Land Big Island of Hawaii. The Big Island of Hawaii is an active volcano that is continually erupting. The lava flows make their way to the ocean, where they cool and form rock. Primary succession is continually occuring on this newly formed rock. As the rock cools and builds up in one area, the flows continue in different directions. The formation of new land in Hawaii allows biologists to study the processes involved in primary succession.

Are there places on land where no life exists? There aren't many. The lava fields created after a volcanic eruption are lifeless. The lava cools into sterile rock. However, it doesn't take long for life to arrive. Seeds arrive on the wind and in animal droppings, and insects arrive on wind currents. The process of topsoil formation begins as roots erode the newly formed rocks. This slow, gradual process is called primary succession. Then, varieties of organisms move in and begin the formation of new topsoil, and a new set of organisms is able to move in. The first plants and animals to inhabit the bare ground are called pioneer species Opens in modal popup window . During primary succession Opens in modal popup window , the first signs of life occur, typically with the germination of low-growing plants. Primary succession begins with bare land. Slow changes over long periods of time allow more organisms to move into the area. Post fire devastation and renewal Primary succession takes place on newly formed, bare land.

All the populations of organisms in one area make up a community.

As a faint glimmer of light creeps over the horizon, a cheerful symphony of bird melodies echoes through a tall stand of pines at the edge of a glade. A porcupine feeds on skunk cabbage growing beside a stream, and a lone elk pauses to survey the scene. Dawn has come to Chequamegon Forest in northern Wisconsin. Each organism in the forest is a member of the population of individuals of the same species that live in the forest. Together, all the populations of living things in one area—such as this forest—make up a community Opens in modal popup window .

5.03 Ecosystems An ecosystem is made up of a community of organisms and the physical features of their environment. ecosystems are defined areas of various sizes that include biotic and abiotic factors and can change over time.

As winter turns to spring, the temperature rises and snow begins to melt. Insects that were dormant all winter begin to emerge, and animals come out of hibernation. Birds that migrated south return, buds begin to open on trees, and flowers push up from the soil. The organisms in an ecosystem depend on many abiotic features such as temperature, sunlight, and rainfall.

As energy moves from one trophic level to the next, the amount of energy decreases by 90 percent.

As with energy pyramids, food chains and food webs show a definite top-bottom orientation. Producers are on the bottom, while higher-level consumers are on the top. Recall how the amount of energy decreases as it passes up the ecosystem. Don't forget this as you view various food chains and food webs. Review the energy pyramid while you think about the arctic ecosystem. Only 10 percent of the energy contained in a specific trophic level moves to the next level. So, only 10 percent of the energy in the sedge moves to the hare, and only 10 percent of the energy in the hare moves to the hawk.

The biosphere is currently experiencing an unprecedented rate of extinction, most of which is caused by human activity such as pollution and destruction of habitat. The Sixth Extinction Many scientists call today's loss of biodiversity The Sixth Extinction. It's a reference to five earlier, major extinctions in the geologic history of the earth, some of which were caused by major transitions such as climate change or asteroids striking the earth. Read more about this concept in the article "The Sixth Extinction"; its link is listed in the Lesson Resources under Lesson Links.

At several times in the geologic past, the earth experienced mass extinctions, or short periods of time during which a considerable percentage of life on earth went extinct. Those extinctions were caused by several factors: Climate change may have caused some; others were most likely caused by massive asteroids that struck the earth. Review the graph to learn about two main periods of extinction in earth's history: Periods of Extinction Opens in modal popup window . Many scientists today say that we are in the midst of another extinction event just as significant as the one that killed the dinosaurs 65 million years ago. Unlike extinctions in the past, however, this one is being brought about largely because of human activity that has caused habitat loss, pollution, and other phenomena linked to climate change.

All organisms depend on abiotic factors in their environment.

At the most basic level, nearly all organisms rely in some way on the energy from the sun. As you have learned, plants convert the sun's energy into glucose. Plants use the glucose for energy, and other organisms that eat plants obtain the sun's energy indirectly. Organisms also need water for their metabolism to work properly, and most require a certain range of temperatures for survival. Missing Metadata All organisms depend on abiotic factors such as sunlight, water, and a certain range of temperatures.

Different places on earth have different patterns of species diversity. The United States has the most species of freshwater turtles in the world. Australia has the most species of marsupials such as the koala. China has the most species of carnivorous plants such as the pitcher plant. .

Biodiversity usually means the total number of species in an area, but it can also mean the kinds of species present in that area. While tropical rain forests have some of the greatest biodiversity on earth, for some groups of organisms, diversity peaks elsewhere. The United States, for example, has more species of freshwater turtles, salamanders, and freshwater mussels than anywhere else on earth. Australia has more types of marsupials such as koalas, kangaroos, bandicoots, and wombats than any other country. China has more species of carnivorous plants than anywhere else in the world. In analyzing the health of any natural area, both numbers and types of species are important information for researchers.

Biodiversity is all the different kinds of species in an area. Biodiversity Harvard scientist E. O. Wilson first popularized the term biodiversity as a shortened form of the phrase biological diversity. For more than 20 years, Wilson has been a champion of preserving the world's diversity. To find out more about Wilson's views on the current biodiversity crisis, read the article "The Final Countdown"; its link is listed in the Lesson Resources under Lesson Links.

Biodiversity, or biological diversity, is the total of different kinds of organisms in an area. Biodiversity Opens in modal popup window can be an important indicator in how healthy and well-functioning an ecosystem is. To get a sense or measure of biodiversity, scientists define an area and then count the number of all species that live there. Species number is one measurement of biodiversity. The number of species present is also called species diversity. Consider the entire earth. How great is its biodiversity? Scientists have identified 1.7 million species, but experts say that the number of species of plants and animals alone is likely to be 10 times more than that.

More than one food chain often exists in an ecosystem. Unique Food Chains Some food chains don't rely on the sun to start the energy flow. They use a different form of chemical energy. Black smokers are deep-ocean vents that form along the boundaries of the giant plates that move on earth's surface. Food chains and these ocean vents start with sulfur-containing compounds as the original energy source. Instead of photosynthesis, the process of chemosynthesis converts the chemical energy produced by the vents. It is possible that food chains similar to this one exist on other planets and moons in our galaxy.

Deep in a nearby den, a litter of leverets (very young arctic hares) snuggle in their warm home. Below zero winds howl above them. The leverets are part of an intricate ecosystem structure. Soon they will have to compete with a highly populated group of primary consumers, and their instincts will have to protect them from many different species of carnivores. Organisms may be part of many different food chains, but a food chain is always diagramed as a single chain of energy transfers. Observe how the arctic hare fits into the four different food chains at right. What happens when there is more than one type of consumer or more than one type of producer? How can an ecosystem be diagramed then? https://www.pinterest.com/pin/56576539046765709/

Some places on earth are especially rich in species diversity. Tropical rain forests may have hundreds or thousands of tree species, while taigas have only a handful.

Different places on earth have different levels of diversity, which makes sense—some climate patterns may support more species than others. Tropical rain forests, for example, are among the most biologically diverse places on earth. A Brazilian rain forest contains nearly 2,500 different tree species, while the taigas of Finland have only about 30. The difference in number of tree species does not mean that a forest in Finland is less healthy than one in Brazil. But, counting species in each forest gives some baseline for determining changes that occur in each.

A stable ecosystem is one that responds well to change or disturbance.

Ecologists sometimes talk about ecosystem stability, but what does that really mean? You may think that stable means unchanging, but you've just learned that ecosystems constantly experience change. When ecologists talk about ecosystem stability, they are referring to the ability of an ecosystem to respond to change. Scientists today debate the factors that contribute to ecosystem stability, but some argue that a diverse ecosystem—one with many different kinds of species—is more stable than an ecosystem with only few species. Why? Perhaps having many different species provides insurance against environmental changes. For example, if a drought occurs, a diverse ecosystem might have at least a few drought-tolerant plant species that will survive and continue acting as a food supply for the other organisms in the ecosystem. Missing Metadata Some ecosystems, such as old-growth forests, have existed in the same state for hundreds of years, yet are still vulnerable to change.

Ecosystem stability is the ability of an ecosystem to resist significant changes.

Ecosystems always experience change: Trees topple over, animals migrate, and fires occasionally sweep through. When all components of an ecosystem are functioning together, those changes usually don't significantly change the ecosystem. Some changes, however, such as logging or removal of a keystone species, can make the ecosystem less stable and less likely to bounce back after significant change.

Populations of different species grow at different rates. endangered species Many K-strategy animals, such as rhinos, whales, and cheetahs, are endangered. Why do you think that might be? Shows elephants Organisms that represent a K-strategy can have only a few offspring during their lifetime. Shows rats Organisms that represent an r-strategy can have dozens of offspring during their lifetime.

Elephants and whales have only one or two offspring at a time, and their populations grow very slowly. Mice and frogs, on the other hand, have numerous offspring at one time and experience exponential growth when environmental conditions such as food and water are favorable. Elephants and whales represent a type of life history called a K-strategy. Organisms that follow a K-strategy have only a few offspring, don't reproduce until later in life, and tend to have long life spans. Mice and frogs, however, represent a different life history called an r-strategy. Organisms that follow an r-strategy tend to start reproducing at an early age and produce many offspring every time they reproduce.

Your own body contains many ecosystems. Areas of your body, such as your skin and mouth, are ecosystems harboring colonies of microorganisms.

For purposes of scientific study, an ecosystem can even be defined as part of a body. You might not like to think about it, but thousands of microscopic organisms live inside your body. Your mouth, the insides of your digestive system, and even parts of your skin harbor colonies of bacteria and other microorganisms. The fuzzy coating that you feel on your teeth in the morning is actually a biofilm, or a mat of bacteria that grows best in the temperature and pH conditions inside of your mouth. And, the interior of your digestive system contains many species of bacteria that help your body metabolize vitamins and other nutrients. Your digestive system is an ecosystem defined by biotic factors (bacteria that live there) and abiotic factors (the specific temperature, moisture, and pH conditions there).

Freshwater biomes include different types of freshwater ecosystems. Freshwater Biomes To learn more about freshwater biomes, go to the website Kids Do Ecology: Freshwater Biome, which is listed in the Lesson Resources under Lesson Links.

Freshwater biomes include distinct freshwater ecosystems, such as rivers, lakes, and streams, which exist on almost every continent and at almost every latitude. Numerous organisms make their home in freshwater ecosystems, from countless fish species to frogs, turtles, insect larvae, and aquatic birds such as ducks and loons. Freshwater ecosystems also provide food for many land animals such as raccoons, osprey, and muskrats, which feed on the animals that live in the water. Missing Metadata Earth's freshwater biomes include rivers, lakes, streams, ponds, and all other bodies of fresh water.

5.11 Succession Succession occurs when ecosystems change over time through the progressive replacement of species Ecological succession is a gradual change in species composition. There are two types: primary, which occurs on bare land, and secondary, which occurs in a disturbed ecosystem.

Have you ever seen advertisements showing before photos and after photos? Whether for personal improvement or a bathroom renovation, those makeover photos show an obvious contrast. In biology, ecosystems also undergo makeovers. Through various pathways, ecosystems can change over time in a process called succession.

Populations grow exponentially unless certain factors limit their growth.

Have you ever watched as a pond changed from a clear expanse of water in the springtime to a dense mat of green algae by midsummer? If so, you've watched an example of a population of green algae growing exponentially, doubling many times throughout the growing season. Exponential growth Opens in modal popup window occurs when each individual in a population reproduces, the offspring all reproduce, and then the offspring of the offspring reproduce in succession. You can represent exponential growth on a graph.

An ecosystem can change over time.

If significant change occurs in an area, whether natural or human provoked, it affects an ecosystem. The types of biotic factors that can be sustained depend on how significant the changes are. Forces that can change ecosystems include volcanoes, tsunamis, earthquakes, floods, drought, and severe storms such as hurricanes. Look at the photo of a section of rain forest. A dense and diverse rain forest ecosystem once occupied the entire area. Now, the plant and animal life in the cultivated field will be very different, and so will the amount of water, the composition of the soil, and so forth. The field is still an ecosystem with biotic and abiotic factors, but it is very different from what it once was. In this case, the force that changed the ecosystem was human. Missing Metadata A section of rain forest has been cleared and cultivated. The new ecosystem will go through periodic changes as farmers plant and harvest the crops.

The majority of earth's surface is covered by aquatic biomes.

If you look at a photo of the earth from outer space, you can see just how much of the planet is covered with water—more than 75 percent. Collectively, the freshwater and marine regions of the earth make up the world's aquatic biomes. They include marine zones such as coral reefs and the ocean bottom, as well as bodies of freshwater such as rivers, lakes, and streams. More than 75 percent of earth is covered with water.

An ecosystem is made up of a community of organisms and the physical features of the environment.

In any ecosystem, the organisms (biotic factors) that live there depend not only on one another but also on abiotic factors such as sunlight, water, and temperature. Changes in those abiotic factors can affect the organisms living there. Scientists define ecosystems in many ways and at many different levels—an ecosystem can be as large as a prairie or a lake, or as small as the inside of your mouth.

The larger a population gets, the faster it grows.

In any population experiencing exponential growth, the larger the population gets, the faster it grows. In a large population, many individuals are reproducing. For example, a population of 2 cells of algae becomes a population of 4 when those 2 cells divide. A population of 600 cells of algae becomes a population of 1,200 after all individuals divide once. Plotted on a graph, you can see how those populations change very quickly. In theory, all populations—including populations of humans—grow exponentially. But, if all populations grow exponentially, why isn't earth overrun by now?

The availability of resources and the presence of predators are important factors in limiting population growth.

In general, factors such as the availability of food and habitat and the presence of predators keep the exponential growth of populations in check. Any environment has a finite amount of resources that populations can use, and that factor usually limits population growth to a level called the carrying capacity, or K. The carrying capacity Opens in modal popup window is the largest population that a given ecosystem can support at any time. It is determined by the availability of resources such as food and water and the presence of predators. Those factors are called limiting factors because they limit the potential for a population to grow exponentially. On a graph that tracks a population's growth curve, carrying capacity is indicated by the point where the growth rate levels out. That type of graph is called a logistic growth model. Study the graph on-screen. Can you identify the point at which the population reached its carrying capacity? The population reached its carrying capacity at the point where the rising line levels off.

Food chains and food webs illustrate the flow of energy through ecosystems.

In one quick glance, the energy flow through organisms in an ecosystem can be mapped to a food chain. With similar ease, the possible energy pathways within an entire ecosystem can readily be viewed and interpreted through a food web, which is a network of all possible combinations of food chains that are interconnected for a single ecosystem.

The arctic ecosystem contains many organisms.

In the previous lesson's adventure, you traveled to Bracken Cave in Texas. Today, you're headed far north to the arctic tundra to learn what life is like for an arctic hare. The arctic landscape has a short growing period each year and a long, snowy winter. During the winter months, the hare's fur becomes white to camouflage it in the snow. Camouflage is important because carnivores prey on the hare. Added to this ecosystem are the plants that the hare eats, as well as several types of insects that also eat the plants. In this lesson, you'll take a close look at the complex relationships among some of the organisms that make the Arctic their home. Arctic landscape The arctic landscape is lush and green during the summer months. The growing period is short but intense during long days and short nights.

Scientists have organized the biosphere into levels to aid communication.

Just as living organisms are organized into cells, tissues, and organs, the biosphere is organized into different levels. Scientists who work in the field of ecology Opens in modal popup window have defined those organizational levels so they can communicate with each other more effectively. The biosphere Opens in modal popup window is the largest level of organization. Nested within it are five additional levels. Each level is influenced by the interactions of components in the levels above and below it. Ultimately, all living and nonliving things at all levels of the biosphere are connected. Turn to pages 188-189 of your reference book to read more about the levels of ecological organization.

Removing one biotic factor from an ecosystem may have a significant impact on the other biotic factors.

Kelp forests are a unique type of ecosystem in cool marine habitats such as the waters off the California and New Zealand coasts. Kelp, a type of marine alga, anchors to the seafloor and sends long blades up toward the water's surface, creating a rich habitat and food supply for numerous species of marine life. In the early part of the twentieth century, kelp forests along much of the California coast began to disappear. As the kelp disappeared, so did many species of fish and other marine life. What happened? Missing Metadata Kelp forms dense underwater forests that create a habitat for many varieties of marine organisms.

Keystone species help maintain ecosystem stability. What is a keystone? In architecture, a keystone is the wedge-shaped stone at the very top of an arch. It holds all the other stones in the arch in place so the structure can remain strong.

Kelp is a favorite food of marine organisms called sea urchins. Sea urchins are a favorite food of sea otters. Throughout much of the 1800s, sea otters, which were abundant along the Pacific Coast, were hunted for their fur to near extinction. When sea otters were plentiful, they ate enough sea urchins to keep the urchin population in check. Once sea otter numbers declined, sea urchin populations exploded. The urchins began to eat more and more kelp until huge tracts of former kelp forest were left bare. In turn, many fish and other marine species lost an essential habitat. Even the people who made their living fishing on the coast were affected as fish numbers declined. Sea otters in this scenario are an example of a keystone species Opens in modal popup window —a species that plays a key role in maintaining ecosystem stability. By controlling the population of the herbivorous sea urchin, sea otters helped keep the species in the community in balance. When sea otters were removed from the ecosystem, it quickly became unstable. As in this example, keystone species are often predators whose action helps balance the populations of other organisms in the ecosystem. Missing Metadata Sea urchins are a favorite food of sea otters.

Different terrestrial biomes cover the land portion of the earth. Grasslands Some scientists divide the grassland biome into temperate and tropical regions. Temperate grasslands, such as the Great Plains of the United States, experience a wide range of temperatures. Tropical grasslands, such as the African savanna, have consistently higher temperatures and more rainfall than temperate grasslands.

Kenya's Masai Mara National Reserve and the Great Plains of the United States are grassland biomes. The Kenyan grassland is called a savanna, and it is dominated by tall grasses and a few trees. Savannas Opens in modal popup window are characterized by a moderate amount of rainfall and warm to hot temperatures. Geographically, savannas are located in tropical zones. The Great Plains has a wide range of temperatures and receives a moderate amount of rainfall. That type of biome is known as a temperate grassland. Many temperate grasslands have become centers of agriculture because of their fertile soil. Savannas and temperate grasslands are two terrestrial biomes—the biomes that cover the land portion of the planet. The gallery on-screen contains examples of all the major terrestrial biomes on earth. As you view each biome, compare and contrast them. Which abiotic factors characterize each one? Which plant and animal species are dominant there? Read more about the terrestrial biomes on pages 194-197 of your reference book and in the online activity.

Scientists are concerned that many ecosystems are becoming unstable. To read more about studies that scientists are conducting on the growing threat to the world's oceans, go to the website Study Predicts Collapse of All Seafood Fisheries By 2050, which is listed in the Lesson Resources under Lesson Links.

Late in the fall of 2006, scientists made a startling announcement: All species of wild seafood people like to eat—lobsters, tuna, salmon, and many others—are threatened with depletion. In other words, if humans don't change the way they manage the world's ocean ecosystems, the oceans may no longer be able to support healthy populations of important marine species. A combination of factors—including overfishing, pollution, and habitat loss—has begun to destabilize various ocean ecosystems. Oceans perform many important services: They supply our food; they filter pollutants from the water; and they support huge populations of algae that, through photosynthesis, generate much of the air we breathe. For those functions to continue, however, all components of ocean ecosystems—biotic and abiotic—need to be cared for and preserved.

Ecosystems are made of parts that function together. Trophic Levels The first trophic level of any ecosystem is made up of producers - organisms that use the sun's energy to make food through photosynthesis. Plants, as well as some types of algae and bacteria, are producers. The second trophic level of any ecosystem is made up of primary consumers - organisms that eat producers. Many different types of organisms, from birds to prairie dogs to monkeys, are primary consumers. The third trophic level of an ecosystem is made up of secondary consumers - organisms that eat primary consumers. Frogs, snakes, and spiders are all examples of secondary consumers. The fourth trophic level of any ecosystem is made up of tertiary consumers - large predators, such as hawks, that eat secondary consumers.

Like your body, an ecosystem is made of many parts that interact with one another. A change to one part of the system may affect the other parts in different ways. One way that scientist study the makeup of ecosystems is by characterizing how energy flows through them. Ecologists assign the organisms in ecosystems to categories called trophic levels. Energy moves through an ecosystem from one trophic level Opens in modal popup window to the next. Move your cursor over the buttons on the image to read about the organisms that make up each level. You will learn more about trophic levels later in this unit.

Marine biomes include different types of saltwater ecosystems. Marine Biomes To learn more about biomes, visit Kids Do Ecology: Marine Biome, which is also listed in the Activity Resources. Marine biomes include coral reefs, the open ocean, the ocean bottom, and intertidal zones. Estuaries lie at the junction between marine and freshwater biomes.

Marine biomes, which are characterized by salt water rather than fresh water, cover about 70 percent of earth's surface. They support a wide array of life-forms, including crabs, lobsters, shrimp, mussels, whales, corals, algae, and thousands of species of fish. Marine biomes include widely different ecosystems such as coral reefs, the open ocean, the ocean bottom, and intertidal zones. At the edge of many marine biomes is a unique type of ecosystem called an estuary. Estuaries Opens in modal popup window are places where fresh water, such as that from rivers and streams, flows into and mixes with sea water. Estuaries play a critical role in the perpetuation of many species, as they act as nurseries for the young of many marine animals.Turn to pages 198-199 of your reference book to read more about freshwater and marine biomes.

A community and its nonliving environmental features make up an ecosystem.

Nonliving features also influence the makeup of a community. Those features, such as climate, water conditions, and even air quality, influence the types of organisms that can live in a given place. Taken together, a community and its nonliving factors make up an ecosystem Opens in modal popup window . A pond community, for example, is made up of populations of different species. The pond ecosystem, however, also takes into account the nonliving elements such as the quality of the water in the pond, the average weather conditions at the site, and the amount of sunlight that reaches the bottom of the pond.

A community and its nonliving environmental features make up an ecosystem. pond ecosystem Climate, weather, air quality, and amount of sunlight are nonliving factors in this pond ecosystem. Microscopic life-forms are part of the community in this pond ecosystem. Water is a nonliving factor in this pond ecosystem. Different species of plants and animals are part of the community in this pond ecosystem.

Nonliving features also influence the makeup of a community. Those features, such as climate, weather, water conditions, and even air, influence the types of species that live there. Taken together, a community and its nonliving factors make up an ecosystem Opens in modal popup window . Look again at a pond community. It is made up of populations of different species. When looking at this pond as an ecosystem, you also have to take into account the quality of the water in the pond, the average weather conditions, the amount of sunlight that reaches both the top and the bottom of the pond, and so forth. The individuals in an ecosystem depend on nonliving factors just as much as they depend on living factors. If, for example, the water in the pond dried up permanently, then the pond ecosystem would cease to exist and another would take its place.

The balance between biotic and abiotic factors is essential to the survival of many ecosystems.

Off the coast of an island in the Indian Ocean, staghorn coral provides a perfect surface for the feeding and scavenging habits of a variety of marine organisms. Yellowhead butterfly fish, powder blue tangs, and chain moray eels navigate the maze of coral in search of food. Around those unusual marine organisms, countless others make this ecosystem their home. Coral reefs, like all ecosystems, are affected by changes in the environment. Sometimes even a small shift in abiotic factors such as temperature or the salinity of the water can disrupt the natural balance of a coral reef. Most ecosystems, including coral reefs, depend on a delicate balance of biotic and abiotic factors.

Biodiversity is an indicator of a healthy environment. Cougars Cougars play an important role in maintaining ecosystem health in Utah. Read the article "Cougar Predation Key to Ecosystem Health," a 2006 study of cougars in Zion National Park. https://www.sciencedaily.com/releases/2006/10/061024214739.htm

Often one of the first signs that something is amiss in an ecosystem is a drop in biodiversity. In a healthy ecosystem, plants provide the energy base for herbivores whose populations are kept in check by omnivores and carnivores. In Utah's Zion National Park, for example, lush groves of cottonwood trees once grew along stream banks. Numerous other plants, as well as lizards, deer, and butterflies lived in the park. In the last century, however, parts of the park have seen the cottonwood trees disappear and, along with them, the many species that depended on the trees for habitat. Stream banks also began eroding when the roots of the trees could no longer hold the soil in place. What happened? It turns out that cougars, a natural predator of deer, had been mostly driven out of the park by development that brings in thousands of visitors every year. And without cougars, deer populations grew exponentially. The deer began to eat the young cottonwood trees and nearly wiped them out from many parts of the park. The loss of the cottonwoods affected all organisms that depended on the trees for habitat. Missing Metadata When cougars disappeared from Zion National Park, the deer population grew dramatically.

A glacier receding back up a mountain exposes an area where primary succession can occur.

Once an image of vast ice and snow, many mighty glaciers are melting away at record rates. Because of climate change, many glaciers worldwide are retreating. The underlying bare rock surface they reveal is devoid of plant life, giving rise to sites where primary succession can occur. As the process of succession creates soil, over time the once empty rock surfaces will become densely populated forests or lush grasslands. Glacier receeding As glaciers retreat, they leave bare rock surfaces that are devoid of plant life. Primary succession occurs as a series of organisms moves in.

Changes in an ecosystem's abiotic factors affect the organisms living there.

One hot topic in the news is how climate change may affect ecosystems. Scientists suggest that as the earth's climate warms, many plant species that thrive in cooler conditions will need to migrate northward and may even go extinct in the southern end of their range. The level of carbon dioxide (CO2) in the atmosphere may also be increasing. One effect of this rise in carbon dioxide may be that the oceans take up more of this gas than they have in the geologic past. The addition of carbon dioxide makes ocean water more acidic. If left unchecked, increasingly acidic ocean water may be harmful to shelled animals such as clams, mussels, and scallops, as well as reef-building corals. The point is that ecosystems change in response to many different factors, including changes in biotic and abiotic factors. Missing Metadata Changing abiotic factors, such as the level of acidity in ocean water, can harm ecosystems.

Changes in habitat often lead to biodiversity losses. Biodiversity Hotspots Scientists have begun to call some places in the world biodiversity hotspots. Those places not only have a high diversity of unique species, but also are under significant threat from habitat change because of factors such as logging and agriculture. To learn more, read the article "Conservationists Name Nine New 'Biodiversity Hotspots' "; its link is listed in the Lesson Resources under Lesson Links.

One of the biggest threats to biodiversity today is habitat loss. When habitats are significantly changed, such as when forests are cut down for their lumber or open prairies are paved over to create roads and developments, most species that live there lose their homes. It's easy to see that such dramatic habitat changes would lead to a drop in biodiversity—the organisms living in a significantly altered area simply have to find new homes or they will die. But, other habitat changes also can lead to a drop in diversity. Numerous scientific studies show that fragmented habitats support fewer species than intact habitats do. One study showed that bird nests in fragmented forest patches have a much higher risk of predation by cats, dogs, raccoons, and other animals than bird nests in intact forests. Those predators often live in suburban habitats at the edge of forests, but are very rare in large, unbroken tracts of forest. Missing Metadata Development destroys habitat and affects the biodiversity of an area.

Loss of biodiversity can be harmful to people.

Preserving biodiversity is important not just because we like to have lots of different plants and animals to look at, or even because we need to preserve species that might provide us with useful medicines someday. Increasingly, some scientists are beginning to make connections between biodiversity and human health. Changes to environments, they are finding, can have harmful effects on people. One recent study, for example, found that communities near regions with healthy, intact forests with high species diversity have fewer reports of Lyme disease, an infection carried by a type of tick, compared with regions with lower species diversity.

Communities of organisms, together with their surrounding environment, make up an ecosystem.

Put all of the populations of living things of a certain area together, and what do you have? A community. Add to that community the physical environment and all of the abiotic factors in the area, and what do you have? An ecosystem. Both communities and ecosystems are dynamic—that is, they are capable of change. The living components of an ecosystem are biotic factors, and the nonliving ones are abiotic factors. All elements interact either directly or indirectly to form a web of connections that is the ecosystem.

Secondary succession occurs when one community of organisms replaces another.

Raising her nose to the air, a local forest ranger picked up the smell of burning trees. Low-level grass fires are common in this area, but on this summer day in 1988, the wind was brisk, causing a full-blown canopy fire. A canopy fire reaches high into the treetops. Forest fires are a natural part of ecosystems in the Yellowstone National Park, but the summer of 1988 was unusual. Before the fire was done, 1.2 million acres were burned. However, the scarred area would rebound and grow again. The sequential process of changes in plant and animal life in an established ecosystem is called secondary succession. Secondary succession Opens in modal popup window can only occur after an ecosystem is in place. Forest fire Overnight, this forest that was filled with old, hardwood trees was reduced to ash. What will happen to this area next?

Scientists define the boundaries of ecosystems in different ways.

Scientists study ecosystems in different ways and for different purposes, yet an ecosystem is a difficult thing to describe. For one thing, ecosystems vary significantly by size. An ecosystem can be as broad as an entire landscape or as small as a tide pool. The deserts of the American Southwest and northern Mexico make up a large area with similar vegetation that scientists call a biome. But within that broad expanse of deserts are thousands upon thousands of different ecosystems. A rotting cactus—or a twisting river, or a water hole, or 10 square miles of pebble-covered land—might be considered an ecosystem.

Every living thing is part of earth's biosphere. populations are made up of individuals that grow exponentially but limiting factors cause them to grow logistically. What comes to mind when you think of the environment? Maybe a thick, green jumble of tropical rain forest? A grassy meadow with a cool stream running through it? Or maybe a coral reef teeming with fish, sea turtles, and countless other forms of marine life? The organisms in each of those environments interact in many different ways. Ecology is the study of living things and how they interact with each other and with their environment. In this unit, you will learn about the levels of ecological organization, how organisms interact among those levels, and how energy flows from one level to another.

Seen from outer space, earth looks like a swirly blue marble. On that blue marble are living things, from the bottom of the oceans to the top of the highest mountains. That zone of life is like a shell that contains all organisms. Scientists call that zone the biosphere. In this lesson, you will learn about how the biosphere is organized and how the environment affects the organisms within it.

Biodiversity is the total of all the species living in a given area.

So far, scientists have catalogued 1.7 million different species of plants and animals, but that's only a fraction of the amount of biodiversity on the planet. Some places, such as tropical rain forests, are very diverse, while other places, such as the forests of northern Canada, have far fewer species. Biodiversity is an indicator of ecosystem health, and changes to the ecosystem can often result in a loss of biodiversity. Protecting biodiversity is an important goal: People have found countless uses for different species on earth, and future research is sure to turn up more.

Energy can flow through multiple pathways in a food web.

Something has disturbed a wolverine. Its bared teeth show that the largest member of the weasel family will not back down. The wolverine was interrupted as it was scavenging a dead caribou. The wolverine is a scavenger, which is a type of detrivore. How do scavengers, decomposers, and parasites affect a food web? Since they are specialized consumers, the arrows and energy flow to them. In a complex food web, energy can flow along complex pathways from producer to top-level consumers, including decomposers and detrivores. Wolverine Wolverines are scavengers, and they will viciously defend a carcass. There are many specialized roles for consumers in an ecosystem.

A biome is a large geographic area dominated by specific kinds of plants and animals.

The broadest level of ecological organization is the biome, the name for a large region characterized by certain kinds of plants and animals. Abiotic factors, such as climate and precipitation, determine the makeup of earth's terrestrial biomes. Aquatic biomes, including marine and freshwater systems, cover the vast majority of earth's surface.

Human activities have caused many ecosystems to become unstable. The Dead Zone For more information about the depletion of oxygen in the Gulf, go to the website Gulf of Mexico Dead Zone, which is listed in the Lesson Resources under Lesson Links.

There is section of the Gulf of Mexico covering as much as 7,000 square miles that is called a dead zone. What is this dead zone, and how did it form? The water in that part of the Gulf contains almost no oxygen. The oxygen was depleted in part by a massive population explosion of algae. As the algae died off and decomposed, the dissolved oxygen in the water was depleted. The result? Water with hardly enough oxygen to sustain life. Scientists say that farming practices along the Mississippi River are major contributors to this dead zone—fertilizer from agricultural fields makes its way to the Mississippi River and eventually to the Gulf of Mexico, where the excess fertilizer encourages the growth of algae. The large population of algae completely alters the local food web, eventually leading the ecosystem to collapse.

Temperature and precipitation are key factors in shaping biomes.

Think again about the two biomes described on the previous screen. A desert is a place with very little rainfall. The plants that grow there must be adapted to conserve water and extract water from deep in the soil. The animals in the desert must also be efficient at using water. A tropical rain forest, in comparison, is a place with high temperatures and high humidity. Many kinds of plants grow in tropical rain forests, and many kinds of animals specialize on those plants as a food source. Temperature and amount of precipitation, therefore, are two key factors that determine the makeup of any biome.

Populations of different species make up a community.

Think of a pond in the summertime. Fish swim in the water, frogs hop along the shore, mosquitoes lay their eggs in the water, many plants grow from the soil on the pond bottom and at the water's edge, and large animals such as raccoons and herons feed on some of the pond's inhabitants. The organisms living in and around a pond make up a community. A community Opens in modal popup window is an ecological level made up of populations of different species that live in a specific location. The frogs make up one population in the pond community, the lily pads make up another, the mosquitoes make up another population, and the raccoons make up still another. In a pond, as in any community, the organisms depend on one another.

A food web represents many interconnected food chains within the same ecosystem. http://apassionforscience.pbworks.com/w/page/64065414/1E2_2013%20Group%208%20-%20Polar%20Region Reality Check Think about it. The complete arctic food web must be much more complex than this. The diagram provides a simple interpretation of the arctic food web. In reality, the complete web would include many more organisms. To complicate the story even further, some animals such as the rough-legged hawk do not live in the Arctic year-round. They migrate to the region for short periods of time; therefore, they may play roles in two different food webs depending on the time of year. In addition, humans are part of the Arctic food web. Inuit hunters act on many different trophic levels.

To paint a larger picture of the relationships in an ecosystem, biologists combine the food chains together to form a diagram called a food web. The energy flow in a food web Opens in modal popup window follows along any number of pathways. Explore the Arctic food web to find out how all the food chains come together to form a food web. Notice how important the hare is in the food web. It is food for many different predators, and it eats different organisms. As you've probably already figured out, a food web gives a more complete picture of what is going on in an ecosystem. Arctic Food Web Opens in modal popup window There are a wide variety of ecosystems on earth. More are discovered and studied every year. Turn to page 205 of your reference book for another example of a food web.

A large area can be an ecosystem, and parts of that area can be ecosystems as well. The 700-square-mile Okefenokee Swamp is a large ecosystem with many smaller ecosystems contained within it. Clumps of reeds, groups of aquatic plants, stretches of open water, and stands of trees form smaller ecosystems within the swamp.

To understand the scope of the term ecosystem, let's look at the Okefenokee Swamp in Georgia. The entire 700 square miles of the swamp can be called an ecosystem. It consists of all biotic factors (plants, animals, and microorganisms), as well as abiotic factors such as light, temperature, and even the chemical makeup of the water. But for purposes of scientific study, it is also possible to call a small patch of reeds in that swamp an ecosystem, too. The patch of reeds is home to a specific range of animals and plants and has specific abiotic factors. Likewise, a wooded island in the swamp or an expanse of open water can be called an ecosystem.

Ecosystems perform many important functions. Ecosystem Services To learn more about the many important services that ecosystems perform, go to the website Ecosystem Services: A Primer, which is listed in the Lesson Resources under Lesson Links.

Wetlands are important ecosystems that filter and clean groundwater. They also act as a natural barrier against flooding during heavy rains or coastal storms. Coastal wetlands called estuaries Opens in modal popup window carry out those functions and also serve as nursery sites where fish and other species begin their lives. Many marine organisms that are popular as seafood start their lives in estuaries. Forests are also important ecosystems for the many species that live there, and for people as well. The paper you write on, the wood your furniture is built from, and the logs you might burn in your fireplace all come from forests. Some of the oxygen in the air you breathe is generated by forest plants. Ecosystems provide countless services to humans, many of which you've probably never thought about. For ecosystems to carry out those services, they need to be stable. Missing Metadata Estuaries, which are coastal wetlands where rivers or streams meet the sea, filter groundwater and act as nurseries for many species of marine life.

5.06 Biodiversity Biodiversity is the total of all species living in a given area. biodiversity is the total of all species in an area and is different in different parts of the world. Biodiversity indicates ecosystem health but faces threats today.

What kind of an event would send teams of scientists crawling through the dirt, scavenging roadkill, and climbing trees all through the night? It's BioBlitz, a 24-hour inventory of all living things that they can find in parks and natural areas around the world. BioBlitz is a public activity designed to expand our understanding of biodiversity—the sum total of all organisms living in a given area.

Ecosystems experience change.

While the ecosystems that you are familiar with—lakes, wetlands, and forests—may look constant and unchanging, nothing could be further from the truth. Change is always present in ecosystems: Trees may die and topple over, a drought may kill off many plants, species may migrate throughout the year, and ocean waves may flip rocks and boulders. Those and countless other factors produce change in ecosystems. Yet, ecosystems usually don't collapse after a storm or after a tree falls. Ecosystems can usually bounce back after those and other kinds of disturbances. Let's continue to explore how ecosystems respond to change. Missing Metadata A drought disrupted this ecosystem but, given the right conditions, the ecosystem will recover in time.

Extinction and extirpation cause a loss in biodiversity.

When a species disappears from the earth, it is said to have gone extinct. Every extinction represents an irreversible loss of biodiversity. And as you have learned, losing a species can have damaging effects on an ecosystem. Think about the interconnectedness of a food web and you'll see why. What happens, for instance, if a bird that plays an important role as a pollinator or seed disperser goes extinct? You'll see a ripple effect in the ecosystem: Plants that depended on that bird might become extinct as well, and in turn, animals that depended on those plants may also suffer. Removal of a species from part of its range—a process called extirpation Opens in modal popup window —also has a significant effect on ecosystems. Wolves used to roam the forests of Wisconsin, and they kept populations of white-tailed deer under control. During the 1800s and 1900s, wolves were hunted to near extinction in that part of the state. As a result, deer populations exploded, and the deer changed the forests by eating tree saplings and forest flowers such as lilies and certain rare orchids. When those plants are gone, the loss will affect other species that rely on them. Missing Metadata When wolves in certain states were killed off, deer populations exploded.

5.05 Biomes A biome is a large geographic area dominated by specific kinds of plants and animals. Biomes are large geographic regions in which temperature and precipitation determine dominant plants and animals.

When you think about a tropical rain forest, you probably envision lush plant life, parrots, and maybe a jaguar. If someone asked you where you'd expect to find cacti growing, you'd say the desert. Tropical rain forests and deserts are two types of biomes—large geographic areas with certain climate conditions that are dominated by specific plants and animals.

Climate determines where different species live.

Where would you expect to find a polar bear? How about a panda? A koala? Each of those animals lives in a different geographic location, and is adapted to the food sources and climate in its own habitat. Koalas, for example, live in dry forests in Australia and feed exclusively on eucalyptus Opens in modal popup window , a type of tree that grows there. Pandas live in temperate forests in China, where they feed on bamboo. Carnivorous polar bears live in the icy Arctic, where their white fur blends in with the background and helps them sneak up on prey. At a global level, different geographic regions can be broadly characterized by their climate and the dominant species of plants and animals that live there. Those large areas of earth, defined by climate and the organisms that live there, are called biomes. The biome Opens in modal popup window is the broadest level of ecological classification within the biosphere. Find out more about the earth's major biomes on pages 194-195 of your reference book and in the online activity.

Ecosystems do not always have sharp physical boundaries. Processes in one ecosystem may have an impact on another ecosystem.

While people often talk about ecosystems as though they are disconnected from each other, no ecosystem is completely disconnected from others. Organisms may sometimes move from one ecosystem to another, and weather events in one ecosystem may have an effect on another. For example, after an especially snowy winter in the mountains, the valley ecosystem below will experience higher than usual river levels in the springtime as the snow melts. Missing Metadata A change in one ecosystem can have an impact on another.

People rely on biodiversity in many ways.

Why are some scientists concerned about preserving biodiversity on earth? While it's nice to recognize the pleasing qualities of nature itself, people rely on biodiversity in many ways. Consider some of the medications you have in your own medicine cabinet. Did you know that the active compound in aspirin comes from the bark of willow trees? Or that a blockbuster drug for certain types of cancer comes from a tree that grows only in the Pacific Northwest? In addition, some severely ill patients are benefiting from a powerful painkiller developed from a protein found in the toxin of certain deadly cone snails in tropical coral reefs. The U.S. Army has even worked with a company to develop bandages that cause deep wounds to instantly clot. The magic ingredient in the bandage? A molecule called chitosan, which is made from shrimp exoskeletons. Missing Metadata Many common medications are derived from plant compounds.

Trophic levels interact to make a food web.

You may have heard of a food chain Opens in modal popup window , which is a straight pathway that energy follows from producer Opens in modal popup window to primary consumer Opens in modal popup window to secondary consumer. In the real world, however, the food chain has some kinks in it. A simple food chain, for example, might show an oak tree whose acorns are eaten by a deer, which is in turn eaten by a cougar. At the ecosystem level, however, many more species interact. A more realistic picture might show that squirrels and insects also feed on the oak tree and its acorns, and that foxes and hawks eat the squirrels. So the interaction among organisms is actually more of a food web Opens in modal popup window . A well-functioning ecosystem depends on many interactions between trophic levels to keep energy flowing. Study the simple food chain on-screen, and then review the Food Web, which includes some of the organisms in this food chain.

The existence of biomes is a result of abiotic factors. Temperature and amount of rainfall are two key abiotic factors that dictate the characteristics of biomes. The Antarctic Desert? You may think of deserts as hot places, but they can also be very cold. In fact, a desert is simply a place that receives less than 25 cm (10in.) of rain a year. Many scientists consider the continent of Antarctica to be a desert because it receives very little precipitation.

You're probably familiar with some of the world's biomes, such as deserts, tropical rain forests, and temperate forests. Think about those first two biomes: deserts and tropical rain forests. What makes them different from each other? The abiotic factors in each region—which include temperature, rainfall, and soil characteristics—are very different. As you'll see, temperature and amount of rainfall are two of the key abiotic features that shape biomes.

ecosystem

a community or group of organisms living and interacting with each other and their environment

population

all of the members of one species that live in a common area and whose population dynamics are different from those of other populations

community

all of the populations that live and interact with each other in a particular area

biotic

relating to factors that are associated with or result from the activities of living organisms

food web

the pathway along which food is transferred from one organism to another

ecology

the scientific study of the interrelationships between living things and the environment