Bio 2 Final (ch 18, 19, 20)

life table and survivorship curve

(a) This life table lists the number of survivors remaining each year out of a group of 1000 yellow-eyed penguins that hatch at the same time. (b) A survivorship curve is a graph of the data in a life table. The curve reveals that most penguins die before age 1, after which the death rate levels off.

Age Structure image

(a) This white oak population is dominated by younger individuals, indicating high potential for future reproduction. (b) This population of cottonwoods has few individuals in the youngest age classes. The old trees will likely die soon. Lacking young trees to take their place, the population is probably doomed.

Exponential Population Growth graph

A characteristic J-shaped curve emerges when exponential growth is plotted over time. For a population of rotifers with unlimited resources, the number of individuals added each day increases with each generation. Colored rows in the table represent time points that are labeled in the graph. The graph shows the size of each generation and plots the running total on a graph.

Why is the carrying capacity of a habitat typically not fixed?

A drought that lasts for a decade may be followed by a year of exceptionally heavy rainfall, causing a flush of new plant growth and a sudden increase in food availability for animals. Alternatively, the food on which a species relies may disappear, or a catastrophic flood can drastically reduce the carrying capacity as habitat is destroyed.

Aquatic Biome: (Freshwater Biome) Running water: rivers

A river carries water and sediment from land toward the ocean, providing moisture and habitat to aquatic and terrestrial organisms. At the headwaters. the water is clear, the stream channel is narrow, and the current may be swift. Turbulence mixes air with water, so the water is rich in oxygen. Algae, mosses, and insects cling to any available surface, such as rocks and logs. The river widens as small streams drain additional land areas and contribute water, sediments. and nutrients. As the land flattens, the current slows. The river is now murky, restricting photosynthesis to the banks and water surface. As a result, the oxygen content is relatively low. Typical animals in a slow-moving river include crayfish, snails, bass, and catfish: worms burrow in the muddy bottom.

How organisms balance reproduction with other requirements

A species' life history reflects a series of evolutionary trade-offs; time, energy, and resources are limited. A juvenile organism divides its efforts among growth, maintenance, and survival. After maturity, reproduction joins the list. Reproduction is costly: Many animals devote time and energy to attracting mates, building and defending nests, and incubating or gestating offspring. Once the young are hatched or born, the parents may feed and protect them. All of these activities limit a parent's ability to feed itself, defend itself, or reproduce again. In plants, the reproductive investment is also substantial. Flowers, fruits, and defensive chemicals cost energy to produce and may take away from a plant's photosynthetic area, reducing the ability to capture sunlight. Timing is also critical: An organism that delays reproduction for too long may die before producing offspring. Reproducing too early diverts energy away from growth and maintenance that is crucial to survival.

Explain deserts

Air that rises near the equator also travels north and south. As the air cools at higher latitudes, its density increases, and it sinks back down to Earth at about 30° North and South latitude. Here the warming air absorbs moisture from the land, creating the vast deserts of Asia, Africa, the Americas, and Australia.

Herbivore, predator, and prey interaction

All animals must obtain energy and nutrients by eating other organisms, living or dead. An herbivore is an animal that consumes plants; a predator is an animal that kills and eats other animals, called prey. As in parasitism, the fitness of the herbivore or predator increases at the expense of the organism being consumed. In some cases, predator—prey interactions are directly responsible for fluctuations in an animal's population.

niche

All resources a species requires for survival, growth, and reproduction. Includes the habitat, temperature, light, water availability, salinity, fire, and other abiotic conditions where the species lives. Biotic interactions, such as an organism's place in the food chain, are part of the niche too.

Aquatic Biome: (Marine Biome) Intertidal zone

Along coastlines, the intertidal zone is the area between the high tide and low tide marks. This region is alternately exposed and covered with water as the tide rises and falls. A sandy beach is one familiar example. Constantly shifting sands mean that few producers can take root on the beach, but ocean water delivers a constant supply of organic matter that feeds crabs and shorebirds. In a rocky intertidal zone. seaweeds and mussels attach to rocks, whereas sea anemones, sea urchins, sea stars, and snails occupy the small tide pools.

Aquatic Biomes/Ecosystems

Although terrestrial biomes are most familiar to us, the aquatic ecosystems illustrated in figure 19.9 occupy much more space. Water moves continuously among the ocean, atmosphere, land surface, and groundwater, providing vital connections among all biomes. Section 19.7 describes the water cycle in detail.

Aquatic Biome: (Marine Biome) Estuary

An estuary is an area where the fresh water of a river meets the salty ocean. When the tide is out, the water may not be much saltier than water in the river. The returning tide, however, may make the water nearly as salty as the sea. Organisms that can withstand these extremes receive nutrients from both the river and the tides. Estuaries therefore house some of the world's most productive ecosystems. In the open water, phytoplankton account for most of the productivity, whereas salt-tolerant plants dominate the salt marshes that often occur along the fringes of an estuary. Together, these producers support many species of fish, shellfish, and migratory birds.

Equator and areas away from equator temperature

At the equator, the sun is overhead all year; equatorial regions therefore receive the most intense sunlight, and the temperature is warm year-round. Thanks to Earth's curvature, however, the sun's rays hit other parts of the surface at a slant. Because the same amount of sunlight is distributed over a larger area, the average temperature falls with distance from the equator.

Different levels of ecological relationships (biggest to smallest)

Biosphere, ecosystem, community, population, organism

Human population worldwide

By late 2014, the world's human population was well over 7 billion. Earth's land area is about 150 million square kilometers, population density is about 47 people per square kilometer, but distribution is not random. The highest population densities occur along coastlines and in valleys of major rivers; few people live on high mountains, in major deserts, or Antarctica. China and India account for 1/3 of all humans. The human population growth rate is about 1.1% per year and declining.

A Population's Size and Density

Change Over Time

Major Terrestrial Biome: Polar ice [Climate, Soil, Plants, Animals?]

Climate: Both Antarctica and the Arctic ice cap are extremely cold, dry, and windy year-round. Soil: None. Plants: None. The primary producers in ice and the surrounding ocean are phytoplankton. The light passing through the ice is dim, even in the summer. Animals: The phytoplankton support a unique food web consisting of worms, crustaceans, and icefishes. All of these organisms have antifreeze chemicals that prevent deadly ice crystals from forming in their cells. Larger animals that exploit the Arctic food web have insulating fat and either fur or feathers. Examples include polar bears, seals, whales, and birds. On Antarctica, vertebrates include penguins and seals. Whales and squid inhabit the waters surrounding Antarctica as well.

Major Terrestrial Biome: Desert [Climate, Soil, Plants, Animals?]

Climate: Dry with less than 20 cm of rainfall per year. The temperature can vary dramatically. In a hot desert such as the Sonoran, which spans parts of Arizona and Mexico, the days can be scorchingly hot. In China's cold Gobi Desert the average temperature is below freezing. Soil: Dry soils have little to no organic matter. Plants: Desert plants often have long taproots. quick life cycles that exploit the brief rainy periods, fleshy stems or leaves that store water, and spines or toxins that guard against thirsty herbivores. Animals: Most burrow or seek shelter during the day, then become active at night. Standing water is scarce, so most water comes from the animal's food. Herbivores include jackrabbits and kangaroo rats, which eat seeds and leaves. Snakes and cougars hunt the herbivores.

Major Terrestrial Biome: Temperate coniferous forest (also called temperate rain forest)[Climate, Soil, Plants, Animals?]

Climate: Mild winters, cool summers, and abundant rain and fog. Water is plentiful. Soil: Deep, well-drained, somewhat acidic, and high in organic matter. Plants: Most trees are evergreens such as spruce, cedar, Douglas fir, and hemlock, all of which have waxy, needlelike leaves adapted to year-round photosynthesis. Moisture-loving mosses, ferns, and lichens cover nearly every surface. Animals: Many fishes, amphibians, birds, small mammals, and deer consume the plants and invertebrates in the forest and its streams. Owls, black bears, and cougars hunt small animals.

Major Terrestrial Biome: Temperate grassland [Climate, Soil, Plants, Animals?]

Climate: Moderately moist, with hot summers and cold winters. Soil: Deep, dark, and fertile. Plants: Wind-pollinated grasses dominate, although other flowering plants are also common. Summertime drought, along with fire and grazing, suppress tree growth: grasses survive because their perennial buds lie protected below the soil surface. Animals: Bison, elk, and pronghorn antelope, whose teeth and digestive systems are adapted to a grassy diet, were originally the large, grazing herbivores of North America. Other herbivores include prairie chickens, insects, and rodents such as prairie dogs and mice. Some of these small animals burrow into the soil to hide from predators, whereas others have camouflage. Coyotes, bobcats, snakes, and birds of prey feed on the herbivores.

Major Terrestrial Biome: Northern coniferous forest (also called taiga or boreal forest) [Climate, Soil, Plants, Animals?]

Climate: Relatively dry, short summers and long, cold winters. Moisture scarce in winter, when water may remain frozen for months. Soil: Cold, damp, acidic, and nutrient-poor. Plants: Plants include conifers such as spruce, fir, and pine with evergreen needles that resist water loss. Animals: Many migratory birds visit during the summer, whereas the mammals and birds that live in the taiga year-round have thick layers of insulation that retain body heat. Herbivorous mammals, such as caribou, moose, and snowshoe hares, eat whatever vegetation they can find during the cold winters. Others, such as the black bear, hibernate for the winter. Predatory mammals include lynx, gray wolves, and wolverines.

Major Terrestrial Biome: Tundra [Climate, Soil, Plants, Animals?]

Climate: Snow covers the Arctic and Antarctic tundra during the bitterly cold and dark winter. Temperatures venture above freezing for a few months each year. Soil: Poorly drained and rich in organic matter. Below the surface, a layer of permafrost remains frozen year-round. Plants: Permafrost limits rooting depth and prevents the establishment of large plants, but reindeer lichens, mosses, dwarf shrubs, and low-growing perennial plants such as sedges, grasses, and broad-leafed herbs are common. Animals: In the summer, migratory birds raise their young and feed on the insects that flourish in the tundra. Year-round inhabitants of the Arctic tundra include caribou, lemmings, hares, foxes, and wolverines, all of which have thick layers of fat and warm fur. Animal life in the Antarctic tundra is much less diverse.

Major Terrestrial Biome: Mediterranean shrubland (chaparral) [Climate, Soil, Plants, Animals?]

Climate: Summers are hot and dry; winters are mild and moist. Soil: Sandy soils retain little water. Plants: Shrubs and trees have thick bark and small, leathery, evergreen leaves that slow moisture loss during the dry summers. This biome is especially susceptible to fires because the vegetation dries out during the summer. Fire-adapted plants resprout from underground parts or produce seeds that germinate only after the heat of a fire. Animals: Herbivores include jackrabbits, deer, and birds and rodents that forage for seeds under the shrub canopy; some of their predators include coyotes, foxes, snakes, and hawks.

Major Terrestrial Biome: Temperate deciduous forest [Climate, Soil, Plants, Animals?]

Climate: Summers are warm, winters are cold, and rainfall is approximately constant throughout the year. Soil: Nutrient-rich, owing to abundant leaf litter. Plants: The cold winters select for trees such as oak, hickory, and maple that shed their foliage in autumn. Shade-tolerant shrubs grow beneath the trees. Below them, small flowering plants grow in early spring, when light penetrates the leafless tree canopy. Animals: Many of the animals adjust to the seasons by putting on fat in the summer and hibernating in the winter, or they may store seeds and nuts that sustain them when food is scarce. Still others migrate to warmer areas. Herbivores include seed- and nut-eating mice and birds, whitetail deer, and gray squirrels. Red foxes and snakes are common predators.

Major Terrestrial Biome: Tropical rain forest [Climate, Soil, Plants, Animals?]

Climate: Warm and wet year-round. Soil: Rapid decomposition and leaching means soils are nutrient-poor. Plants: Since climate does not limit plant growth, the main selective forces are competition for light and nutrients. Broadleaf evergreen trees with tall, straight trunks form the forest canopy. Vegetation in the shade beneath the canopy includes climbing vines and small plants that grow on the surfaces of other plants. In the deep shade of the forest floor, plants often have large leaves that maximize the capture of scarce light. Animals: These forests house an incredible diversity of arthropods, fishes, amphibians, reptiles, and mammals that eat plants or other animals. Many of these animals have similar adaptations to life in the trees: bright colors that maximize visibility, coupled with loud calls that are audible throughout the forest canopy.

Major Terrestrial Biome: Tropical savanna (grassland with scattered shrub or trees)[Climate, Soil, Plants, Animals?]

Climate: Warm year-round, with distinct wet and dry seasons. Soil: Well-drained, with a thin layer of organic matter. Plants: Perennial grasses dominate along with scattered patches of drought- and fire-resistant trees and shrubs such as palms, acacias, and baobab trees. These plants have deep roots, thick bark, and trunks that store water. Animals: During the dry season, great herds of animals migrate enormous distances in search of water. The Australian savanna is home to many birds and kangaroos, whereas the grassland in Africa features herds of zebra, giraffes, wildebeests, gazelles, and elephants. Lions, cheetahs, wild dogs, birds of prey, and hyenas prey on the herbivores, and vultures and other scavengers eat the leftovers.

Aquatic Biome: (Marine Biome) Coral reef

Coral reefs border tropical coastlines where the water is clear and sediment-free. These vast underwater structures of calcium carbonate are built by coral animals. The tissues of the coral animals house algae that are essential for the coral's—and the ecosystem's—survival. Sunlight penetrates the clear, shallow water, allowing photosynthesis to occur, and constant wave action brings in additional nutrients. The nooks and crannies of the reef provide food and habitat for a huge variety of algae, fishes, sponges, snails, sea stars, sea urchins, sea turtles, and countless microorganisms.

Why are less-developed countries growing at faster rates than more-developed countries?

Each country's economic development influences its birth- and death rates. Population growth is minimal when both birth- and death rates are high (as they were early in human history). Then, in the next stage of the demographic transition, improvements in living conditions and disease control lower the death rate, but birthrates are high. This transitional period therefore sees the rapid population growth typical of the world's less-developed countries. Eventually, however, birthrates fall; the difference between birth- and death rates is once again small. The population's growth rate therefore slows once more. The world's more-developed countries have entered this stage, and a few even have declining populations because death rates exceed birthrates.

biome

Ecologists divide the biosphere into biomes, which are the major types of ecosystems. Forests, deserts, and grasslands are examples of terrestrial biomes. Lakes, streams, and oceans are water-based ecosystems. Each biome is characterized by a distinctive group of species.

How does the physical environment dictate where each species can live?

Ecosystems cannot live without the ultimate abiotic factor: an energy source.

Explain tropical rain forests

Equatorial regions receive not only the most light but also the most precipitation. When sunlight heats the air over the equator, the air rises, expands, and cools. Because cool air cannot hold as much moisture as warm air, the excess water vapor condenses, forming the clouds that pour rain over the tropics.

Fire abiotic factor

Fire is an abiotic condition in some terrestrial biomes. In grass-lands periodic fires kill trees that might otherwise take over. In coniferous forests, many adult trees die in fires, but their cones open and release their seeds only after prolonged exposure to heat. The seeds germinate after the fire, and the young trees thrive with little competition for sunlight or nutrients.

Factors affecting death rate

Heart disease, stroke, lung cancer, and dementia top the list in the developed world. Infectious diseases rank relatively low, thanks in large part to sanitation, antibiotics, and vaccines. In contrast, deadly diseases such as respiratory infections, diarrhea, and HIV/AIDS are more prominent in developing countries. Crowded conditions facilitate the spread of cholera and other waterborne diseases, especially in areas with limited access to clean drinking water. AIDS has taken an especially high toll in sub-Saharan Africa, where the epidemic has significantly increased death rates, and life expectancy has dipped below 50 in some countries.

Herbivore and plant interaction

Herbivores may eat leaves, roots, stems, flowers, fruits, or seeds. The loss of leaf and root tissue reduces the plant's ability to carry out photosynthesis; consumption of flowers or immature fruits and seeds compromises the plant's reproductive success. Natural selection therefore favors plant defenses against herbivory. Some plant species produce thorns, a milky sap, or distasteful or poisonous chemicals that deter herbivores. The spicy hot chemicals in chili peppers, for example, discourage attack by both fungi and small mammals. At the same time, many herbivores have adaptations that correspond to the plant's defenses. The caterpillars of monarch butterflies, for example, tolerate the noxious chemicals in milkweed plants.

Human age structures for the world's three most populous countries

In India and many other less-developed countries, a large fraction of the population is entering its reproductive years, suggesting a high potential for future growth. In the United States, as in many other developed countries, the population consists mainly of older individuals. Such populations are stable or declining. A population's age structure helps predict its future birth rate.

symbiosis

In a symbiosis (literally, "living together"), two species share a close (and often lifelong) relationship in which one typically lives in or on the other. The relationship between symbiotic species may take several forms, defined by the effect on each participant.

ecosystem

Includes the community plus the abiotic, or nonliving, environment. Each community exists within the context of its physical and chemical surroundings.

Freshwater biomes

Lakes and rivers contain only about 0.3% of the freshwater supply; the rest is in groundwater or locked in ice caps and glaciers. Nevertheless, that tiny sliver of the global water "pie" is vital to humans for drinking water and irrigation. Most other terrestrial species rely on this fresh water as well.

Aquatic Biome: (Marine Biome) Open ocean

Largest biome. The oceans, which cover most of Earth's surface, contain 97% of the planet's water. Both light and nutrients are abundant in the shallow waters above the continental shelf, supporting high primary productivity and extensive marine food webs such as the great kelp forests that fringe many cool-water coastal areas. Beyond the continental shelf, the open ocean's photic zone houses phytoplankton and the zooplankton that feed on them; fishes and whales, in turn, scoop up vast quantities of krill and zooplankton. Below the photic zone, light is too dim for photosynthesis, but a continual rain of organic matter supports great numbers of jellyfishes, fishes, whales, dolphins, mollusks, echinoderms, and crustaceans. The communities that occupy hydrothermal vents add biodiversity to the ocean floor.

Aquatic Biome: (Freshwater Biome) Standing water: lakes and ponds

Light penetrates the regions of a lake to differing degrees. The shallow, nutrient-rich shoreline is part of the photic zone, where light is sufficient for photosynthesis. Rooted plants and phytoplankton thrive along the shore, providing food and shelter for invertebrates, fishes, amphibians, and other animals. In open water, phytoplankton are the dominant producers of the photic zone: zooplankton and fishes are typical consumers. But light does not penetrate the deeper water, where scavengers and decomposers such as insect larvae and bacteria rely on organic material from above to supply energy and nutrients.

Besides birth/death rates, what else is a key regulator of population size?

Migration. Immigration has increased the human population in the United States over the past 200 years. Most Americans are immigrants or descended from immigrants, migration is projected to account for most population growth in this country by around the year 2030. Nonhuman species also disperse to new habitats. They may actively swim, fly, or walk; alternatively, wind or water currents may move individuals into or out of a population.

rain shadow

Mountains often block wind and moisture-laden clouds on their upwind side. The rain shadow on the downwind side of the mountain has a much drier climate.

Nutrient availability abiotic factor

Nutrient availability is another abiotic factor that often determines an ecosystem's productivity. On land, soil provides essential mineral elements such as nitrogen and phosphorus. In aquatic ecosystems, both nutrients and sunlight are often scarce, especially with increasing depth and distance from the shoreline.

Life histories reflect the trade off between what and what? What are the 2 types of life histories?

Quality and quantity. Opportunistic and equilibrium.

10 major terrestrial biomes map

The map at the center of the figure shows the ORIGINAL range of each biome. Humans have drastically reduced many natural/original biomes, replacing them with farmland, suburban housing, and cities. Human activities threaten much of the native habitat that remains.

Ecology

The study of interactions/relationships among organisms and the environment.

How and where do seasons occur?

The tilt of Earth's axis accounts for seasonal temperature changes in non-equatorial regions. From March through September, the northern hemisphere tilts toward the sun and experiences the warm temperatures of spring and summer. During the rest of the year, cooler temperatures prevail as the northern hemisphere tilts away from the sun. The seasons are the opposite in the southern hemisphere.

survivorship curve

The values in a life table are often plotted onto a survivorship curve, a graph of the proportion of surviving individuals at each age. The image shows a graph of the values from the penguin life table. Note that the y-axis data are plotted on a logarithmic scale, not a linear one. The log scale makes it easier to see trends along the entire range of values, from 0 to 1000.

Why does the earth have different climates year round? (Ex: north pole and tropical rain forests)

Tilt of the earth's axis

The survivorship curves of many species follow one of three general patterns

Type I species, such as humans and elephants, invest a great deal of energy and time into each offspring. Most individuals live long enough to reproduce, and the death rate is highest as individuals approach the maximum life span. Type II species, including many birds and mammals, may provide a great deal of parental care. However, the threats of predation and disease are constant throughout life, and these organisms have an equal probability of dying at any age. The type II line is therefore straight. Type III species, such as many fishes and most invertebrates and plants, may produce many offspring but invest little in each one. Most offspring of type III species therefore die at a very young age.

Logistic population growth graph

When resources are limited, the number of individuals added each day declines. At the habitat's carrying capacity, births and deaths are equal, and the population no longer grows. Colored rows in the table represent time intervals that are labeled in the graph.

ecosystem

a community plus its nonliving environment, including air, water, minerals, and fire.

coevolution

a genetic change in one species selects for subsequent changes in the genome of another species. Some connections between species are so strong that the species directly influence one another's evolution. Of course, all interacting species in one community have the potential to influence one another, and they are all "evolving together." These genetic changes are considered coevolution only if scientists can demonstrate that adaptations specifically result from the interactions between the species.

population

a group of interbreeding organisms of one species occupying a location at the same time. Humans form a population, as do acacia trees. Same species, same area.

How have flowering plants and insects coevolved?

a plant may rely on one insect species for pollination, and the insect may eat nectar from only that plant. The plant—insect relationship may also select for specialized structures and behaviors, such as plant "homes" for insects that defend the host.

community

all populations of different species that interact in an area. Ex: All of the species in a park. Acacia trees share the landscape with other members of the same community, such as grasses and large grazing animals. Community ecologists study the interactions among these species, such as competition and herbivory.

resource partitioning

another possible outcome of competition besides competitive exclusion, in which multiple species use the same resource in a slightly different way or at a different time. Therefore, coexistence in overlapping niches is also a possible outcome. For example, multiple species of rockhopper penguins live on islands in the southern Indian Ocean, occupying similar niches: The birds all appear similar, and they all eat similar foods. When researchers tracked penguin movements, however, they found that the populations feed in different places and at different times. Their feeding locations and times reduce competition and therefore improve the reproductive success of all populations.

why do birthrates tend to decline as economic development progresses?

availability of family planning programs, which are relatively inexpensive and have immediate results. Social and economic factors play an important role as well. Educated women are most likely to learn about and use family planning services, have more opportunities outside the home, and may delay marriage and childbearing until after they enter the workforce. Delayed childbearing often means fewer children and therefore slows population growth.

Communities interact in

biomes

Most obvious ways to gain/lose members of a population (helps determine population size)

birth and death

life table

chart that shows the probability of surviving to any given age. (Life insurance companies use life tables to compute premiums for clients of different ages.) In the image the declining number of survivors in each age class reflects the effects of predation, disease, food scarcity, and all other factors that prevent an individual from reaching its theoretical life span. Helps determine the pattern of how much energy is invested into offspring, and how many offspring survive long enough to reproduce.

Soil

complex mixture of rock fragments, organic matter, and microbes. Forms the framework of terrestrial biomes, directly supports plant life.

Density-dependent factors (that limit population size)

conditions whose effects increase as a population grows. Most density-dependent limits are biotic, meaning they result from interactions with living organisms. Within a population, competition for space, nutrients, sunlight, food, mates, and breeding sites is density-dependent. When many individuals share limited resources, few may be able to reproduce, and population growth slows or even crashes.

age structure

distribution of age classes, also helps determine its birth rate. A population with a large fraction of pre reproductive individuals will grow. As these individuals enter their reproductive years and produce offspring, the prereproductive age classes swell further, building a foundation that ensures future growth. Conversely, a population that consists mainly of older individuals will be stable or may even decline. This situation can doom a population of endangered plants if, for example, habitat destruction makes it impossible for seedlings to establish themselves. With few young individuals to replace those that die of old age, the population may go extinct.

Density-Independent factors (that limit population size)

exert effects that are unrelated to population density. Most density-independent limits are abiotic, or nonliving. Natural disasters such as fires, earthquakes, floods, volcanic eruptions, and severe weather are typical density-independent factors. A hurricane may destroy 50% of the birds' nests in a forest, without regard to the density of the bird population. A lava flow kills everything in its path. The effects of oil spills and other industrial accidents are density-independent, too. Destruction related to human activities is a density-independent factor that is pushing many species to the brink of extinction.

2 types of population growth

exponential or logistic

The human population has grown

exponentially in the last 2000 years. So far, humans have found ways to escape many of the forces that limit the growth of other animal populations. Yet exponential growth can-not continue indefinitely.

Biologists divide aquatic biomes into two main categories

freshwater and marine (oceans)

equilibrium life history (K-selected life history)

individuals tend to produce a small number of offspring that receive extended parental care. Century plants, birds, and large mammals (including humans) have equilibrium life histories, maturing late and producing only a few offspring throughout their long lives. High parental investment in each offspring means that most live long enough to reproduce, so these species have type I survivorship curves.

opportunistic life history (r-selected life history)

individuals tend to reproduce at an early age and have many offspring that receive little care. The population's growth rate can be very high if conditions are optimal. In general, however, each offspring has a very low probability of surviving to reproduce; this pattern is typical of species with type III survivorship curves. Weeds, insects, and many other invertebrates typically have opportunistic life histories. For example, a pigweed plant sheds 100,000 seeds in the one summer of its life; a female winter moth mates once and lays hundreds of fertilized eggs just before she dies. These and many other organisms mature early, produce many offspring in a single reproductive burst, and die. Although their populations can skyrocket when conditions are favorable, competition for resources and stresses such as frost or drought soon limit their growth.

Dissolved oxygen in aquatic ecosystems abiotic factor

influences the types of microbes and animals that can live in the water. Many organisms are adapted to seawater or salty soil, but others are not.

A primary producer, or autotroph ("self-feeder")

is any organism that can use CO, and other inorganic substances to produce all the organic molecules it requires. This process requires energy. In most ecosystems, the primary producer carry out photosynthesis, using sunlight as an energy source. On land, plants such as trees and grasses are the dominant primary producers. In water, however, most photosynthesis occurs courtesy of phytoplankton. Either way, the organic molecules produced in photosynthesis are eaten by a host of grazers, which are in turn consumed by predators. These herbivores and carnivores are consumers, or heterotrophs.

The science of ecology is global because

life exists almost everywhere on Earth, even in places once thought to be much too harsh to support it. Scientists have discovered life in Arctic ice, salt flats, hot springs, hydrothermal vents, and mines that plunge miles below Earth's surface. All of these areas are part of the biosphere

Natural selection influences

life history

ecological footprint

measures the amount of land area needed to support a country's overall lifestyle. The calculation includes, among other measures, energy consumption and the land area used to grow crops for food and fiber, produce timber, and raise cattle and other animals. The land areas occupied by streets, buildings, and landfills are also part of the ecological footprint, as is land used for waste disposal. Not surprisingly, the world's wealthiest and most populous countries have the largest ecological footprints. Energy consumption accounts for about half of the ecological footprint. The wealthiest countries make up less than 20% of the world's population yet consume more than half of the energy. Less-developed countries, however, will take a larger share of energy supplies as their populations grow and their economies become more industrialized. Since the vast majority of the energy comes from fossil fuels, the result will be increased air pollution and acid rain. Moreover, the accumulation of CO2 and other greenhouse gases is implicated in global climate change. Food production is another significant element of the ecological footprint. Overall, both the demand for food and agricultural productivity rise each year. To boost food production, people often expand their farms into forests, destroying habitat and threatening biodiversity. Because the ecological footprint focuses on land area, it does not include water consumption. Nevertheless, the availability of fresh water has declined worldwide as people have demanded more water for agriculture, industry, and household use. In many poor countries, less than half the population has access to safe water for drinking and cooking.

phytoplankton

microscopic, free-floating, photosynthetic organisms such as cyanobacteria and algae

heterotrophs ("other-feeders")

obtain carbon by eating the organic molecules that make up another organism. herbivores and carnivores are consumers, or heterotrophs.

Biotic interactions

occur among the living species in a community

Competition

occurs when two or more organisms vie for the same limited resource, such as shelter, nutrients, water, light, or food. Many species compete for the same resources. Assuming that neither participant obtains all of the resource, the effects of competition are negative for both.

Marine biomes

oceans cover 70% of Earth's surface and contain 97% of the planet's water; they therefore form the world's largest biome. Most photosynthesis on Earth occurs in the vast oceans, contributing enormous amounts of oxygen to the atmosphere. Moreover, oceans absorb so much heat from the sun that they help stabilize Earth's climate.

Hunting, trapping, and fishing regulations are based on

population estimates, as are decisions on where to build houses, dams, bridges, and pipelines

biosphere

portion of Earth where life exists. Thanks to the global circulation of energy, nutrients, and water, the biosphere forms one huge, interconnected ecosystem. Within the biosphere are prairies, seashores, deserts, jungles, mountain-tops, and a patchwork of other unique landscapes, each with its own set of conditions. The species that are native to each location have adaptations that correspond to these conditions.

Mutualistic relationships

symbioses that improve the fitness of both partners. Flowering plants and their reward-seeking pollinators are a classic example, as are mycorrhizal fungi. In the latter case, the fungus acquires nutrients and water that it shares with its host plant; the plant feeds sugars to its live-in partner. Many of the bacteria in our intestines are also mutualistic; these microbes consume nutrients from our food but also produce vitamins and defend us against disease.

parasitism

symbiotic relationship in which one species acquires resources at the expense of a living host. The most familiar parasites are disease-causing bacteria, protists, fungi, and worms. Some of these organisms can suppress their host's immune system, an adaptation that favors long-term colonization of the body. Plants may also be parasites. Mistletoe, for example, is a parasitic plant that taps into the water-and nutrient-conducting "pipes" of a host plant.

Besides sunlight, the major abiotic factors that determine the numbers and types of plants on land are

temperature and moisture. All organisms are adapted to a limited temperature range; trees cannot live where the temperature is too low (causes a tree line or timberline on mountains). The plants that grow where water/moisture is abundant, such as the tropical rainforest, have different adaptations from a desert ecosystem.

logistic growth model

the early growth of a population may be exponential, but growth slows and stops as the population approaches the habitat's carrying capacity. The resulting S-shaped curve shows this change in the growth rate over time.

photic zone

the layer of water with sufficient light for photosynthesis, and nutrients are most abundant near land. All aquatic communities need sunlight and nutrients. Ecosystem productivity is therefore highest in the shallow, well-lit waters near the shore. In deep water away from the shore, however, both energy and nutrients can be scarce.

carrying capacity

the maximum number of individuals that the ecosystem can support indefinitely. Imposes an upper limit on a population's size.

population's death rate

the number of deaths per unit time, scaled by the population size.

Population density

the number of individuals of a species per unit area or unit volume of habitat.

population's birthrate

the number of new individuals produced per individual in a defined time period. For example, the human birthrate worldwide is about 18.9 births per 1000 people per year. The number of offspring an individual produces over its lifetime depends on how many times it reproduces, the number of offspring per reproduction, and the age at first reproduction. All other things being equal, the earlier reproduction begins, the faster the population will grow.

habitat

the physical location where the members of a population normally live. The ocean, desert, or rainforest are typical examples, but an organism's habitat might even be another organism. Your body, for example, is home to billions of microbes

life history

the series of events in an organism's life from conception through death. The main focus of life history analysis is the adaptations that influence reproductive success. The life history of a species includes its typical developmental rate, life span, social behaviors, reproductive timing, mate selection, number and size of the offspring, number of reproductive events, and amount of parental care. Although every population's size depends in part on birth- and death rates, species differ widely in the timing of these events. Population ecologists therefore find it useful to document a species' life history.

Population ecology

the study of the factors that influence a population's size over time

How ocean currents influence coastal climates

they transport cold and warm water around the globe. For example, bands of cold water flow along the west coast of North America, while currents along the east coast are relatively warm. In addition, large water bodies heat up and cool down much more slowly than does the land. Coastal regions therefore often have milder climates than do inland areas at the same latitude. On a hot summer day, beach-goers notice this effect as they enjoy cooling breezes from the sea. Conversely, during the winter, the ocean releases stored heat.

competitive exclusion principle

two species cannot coexist indefinitely in the same niche. The two species will compete for the limited resources that they both require, such as food, nesting sites, or soil nutrients. According to the competitive exclusion principle, the species that acquires more of the resources will eventually "win." The less successful species dies out. This is how competition can help shape the species composition of a community. Introduced species sometimes displace native species by competitive exclusion. Zebra mussels, for example, are native to the Caspian Sea in Asia. These mollusks were accidentally introduced to the Great Lakes in the 1980s and have since spread to many waterways in the United States and Canada.

Commensalism

type of symbiosis in which one species benefits, but the other is not significantly affected. Most humans, for example, never notice the tiny mites that live, eat, and breed in our hair follicles. Similarly, the reproductive success of a tree is neither helped nor harmed by the moss plants and lichens that grow on its trunk and branches.

The same basic evolutionary process—natural selection—has produced

unique populations and communities of organisms in nearly every possible habitat. Interactions with both the living and the nonliving world shape the adaptations that contribute to survival and reproductive success.

exponential growth

when the number of new individuals is proportional to the population's size; the larger the population the faster it grows. 100 aquatic animals called rotifers are placed in a tank under ideal growth conditions. The amount of new rotifers produced each day depends on the size of the population: the more rotifers in the tank, the larger the capacity to add offspring. Growth resulting from repeated doubling (2, 4, 8, 16, 32) like bacteria, is exponential. Growth is exponential when there are unlimited resources. Species introduced to an area where they are not native may also grow exponentially for a time, since they often have no natural population controls.