Unit 2 chapters 5 & 6

Populations Can Decline Due to a Rising Death Rate: The AIDS Tragedy

A large number of deaths from AIDS can disrupt a country's social and economic structure by removing significant numbers of young adults from its population. According to the World Health Organization, between 1981 and 2012, AIDS killed more than 30 million people (617,000 in the United States). Unlike hunger and malnutrition, which kill mostly infants and children, AIDS kills primarily young adults and leaves many children orphaned, some of whom are also infected with HIV, the virus that can lead to AIDS. Worldwide, AIDS is the leading cause of death for people of ages 15-49.

Empowering Women Can Help to Slow Population Growth

A number of studies show that women tend to have fewer children if they are educated, have the ability to control their own fertility, earn an income of their own, and live in societies that do not suppress their rights. Although women make up roughly half of the world's population, in most societies they have fewer rights and educational and economic opportunities than men have. Women do almost all of the world's domestic work and child care for little or no pay and provide more unpaid health care (within their families) than do all of the world's organized health-care services combined. In rural areas of Africa, Latin America, and Asia, women do 60-80% of the work associated with growing food, gathering, and hauling wood (Figure 6-17) and animal dung for use as fuel, and hauling water. As one Brazilian woman observed, "For poor women, the only holiday is when you are asleep."

Most Populations Live in Clumps

A population is a group of interbreeding individuals of the same species (Figure 5-13). Figure 5-14 shows three ways in which the members of a population are typically distributed or dispersed in their habitat. Most populations live together in clumps (Figure 5-14a) such as packs of wolves, schools of fish (Figure 5-13), and flocks of birds. Southern sea otters (Core Case Study) (Figure 5-1, left), for example, are usually found in groups known as rafts or pods ranging in size from a few to several hundred animals. Why clumps? Several reasons: First, the resources a species needs vary greatly in availability from place to place, so the species tends to cluster where the resources are available. Second, individuals moving in groups have a better chance of encountering patches or clumps of resources, such as water and vegetation, than they would searching for the resources on their own. Third, living in groups provides some protection from predators. Fourth, living in packs gives some predator species a better chance of getting a meal.

How do Environmental Scientists think about human population growth? (2) a. Human Population growth shows certain trends... 1. Growth rate annually has dropped but population continues to grow 2. World's pop growth rate = 1.2% 3. Human growth unevenly distributed...mostly in more developed countries 4. pop growing exponentially in LDC 5. Most people move from rural to urban places b. Human pop growth effects Natural Capital 1. growing pop = growing ecological footprint 2. leads to cultural carrying capacity which is the max # of people who could live in reasonable freedom and comfort indefinitely

a. Human Population growth shows certain trends... b. Human pop growth effects Natural Capital

how do species handle niche overlap?

1 move to another area of plan 2 shift its eating habits 3 natural selection to reduce or alter its niche 4 population decline/extinction

Predators have a variety of methods that help them to capture prey. Herbivores can simply walk, swim, or fly to the plants they feed on.

1. Herbivores: walk swim or fly to plants 2. Carnivores feeding on mobile prey have two main options: pursuit and ambush. Some, such as the cheetah, catch prey by running fast. Others, such as the American bald eagle, can fly and have keen eyesight. 3. Still others cooperate in capturing their prey. For example, female African lions often hunt together to prey on zebras (Figure 3-7), wildebeest, antelopes, and other fast-running large animals of the open savanna grasslands. 4. Camouflage 5. Chemical warfare

what 3 types of resource partitioning are there?

1. evolve specialized traits 2, using resources at different times 3. using them different ways

identify 5 basic interactions of species

1. interspecific competition 2 predation 3 parasitism 4 mutualism 5commensalism

How do species interact? ((7 ways)

1. most species compete with each other 2. some species evolve certain ways to share 3 consumer species feed on other species 4 interactions between predator and prey species can drive each others evolutions 5 some species feed off other species by living off or inside others 6. in some interactions both species benefit 7 in some interactions one species benefits and other is not harmed

Ecological Succession Does Not Follow a Predictable Path

According to the traditional view, ecological succession proceeds in an orderly sequence along an expected path until a certain stable type of climax community occupies an area. On land, such a community is dominated by a few long-lived plant species, often within a mature forest (Figures 5-11 and 5-12), and is in balance with its environment. This equilibrium model of succession is what ecologists once meant when they talked about the balance of nature. Over the last several decades, many ecologists have changed their views about balance and equilibrium in nature. There is a general tendency for succession to lead to more complex, diverse, and presumably sustainable ecosystems. However, a close look at almost any terrestrial community or ecosystem reveals that it consists of an ever-changing mosaic of patches of vegetation in different stages of succession. The current scientific view is that we cannot predict a given course of succession or view it as inevitable progress toward an ideally adapted climax plant community or ecosystem. Rather, ecological succession reflects the ongoing struggle by different species for enough light, water, nutrients, food, space, and other key resources. Most ecologists now recognize that mature, late-successional ecosystems are in a state of continual disturbance and change.

Living Systems Are Sustained through Constant Change

All living systems, from a cell to the biosphere, are constantly changing in response to changing environmental conditions. However, living systems contain complex processes that interact to provide some degree of stability, or sustainability, over each system's expected life span. This stability, or capacity to withstand external stress and disturbance, is maintained only by constant change in response to changing environmental conditions. For example, in a mature tropical rain forest, some trees die and others take their places. However, unless the forest is cut, burned, or otherwise destroyed, you would still recognize it as a tropical rain forest 50 or 100 years from now. It is useful to distinguish between two aspects of stability or sustainability in living systems. One is inertia, or persistence: the ability of a living system such as a grassland or a forest to survive moderate disturbances. A second factor is resilience: the ability of a living terrestrial system to be restored through secondary ecological succession after a more severe disturbance.

A Population's Age Structure Helps Us to Make Projections

An important factor determining whether the population of a country increases or decreases is its age structure: the numbers or percentages of males and females in young, middle, and older age groups in that population (Concept 6-3). Population experts construct a population age-structure diagram by plotting the percentages or numbers of males and females in the total population in each of three age categories: prereproductive (ages 0-14), consisting of individuals normally too young to have children; reproductive (ages 15-44), consisting of those normally able to have children; and postreproductive (ages 45 and older), with individuals normally too old to have children. Figure 6-11 presents generalized age-structure diagrams for countries with rapid, slow, zero, and negative population growth rates.

Women Are Having Fewer Babies but the World's Population Is Still Growing

Another measurement used in population studies is the fertility rate, a measure of how many children are born in a population over a set period of time. Here, we consider two types of fertility rates, the first being the replacement-level fertility rate: the average number of children that couples in a population must bear to replace themselves. It is slightly higher than two children per couple (2.1 in more-developed countries and as high as 2.5 in some less-developed countries), mostly because some children die before reaching their reproductive years. Any fertility rate above the replacement level will cause a population to grow.

Human Population Growth Impacts Natural Capital

As the human population grows, so does the global total human ecological footprint (see Figure 1-13), and the bigger this footprint, the higher the overall impact on the earth's natural capital. The 2005 Millennium Ecosystem Assessment concluded that human activities have degraded about 60% of the earth's ecosystem services (Figure 6-4).

Populations Made up Mostly of Older People Can Decline Rapidly

As the percentage of people age 65 or older increases, more countries will begin experiencing population declines. If population decline is gradual, its harmful effects usually can be managed. However, some countries are experiencing fairly rapid declines and feeling such effects more severely. Japan has the world's highest percentage of elderly people (above age 65) and the world's lowest percentage of young people (below age 15). In 2012, Japan's population was 128 million. By 2050, its population is projected to be 95.5 million, a 25% drop. As its population declines, there will be fewer adults working and paying taxes to support an increasing elderly population. Because Japan discourages immigration, it may face a bleak economic future. As a result, some have called for the country to rely more on robots to do its manufacturing jobs and on selling robots in the global economy to help support its aging population.

In Some Interactions, One Species Benefits and the Other Is Not Harmed

Commensalism is an interaction that benefits one species but has little, if any, beneficial or harmful effect on the other. One example involves plants called epiphytes (air plants), which attach themselves to the trunks or branches of trees (Figure 5-10) in tropical and subtropical forests. Epiphytes benefit by having a solid base on which to grow. They also live in an elevated spot that gives them better access to sunlight, water from the humid air and rain, and nutrients falling from the tree's upper leaves and limbs. Their presence apparently does not harm the tree. Similarly, birds benefit by nesting in trees, generally without harming them.

Different Species Have Different Reproductive Patterns

Different reproductive patterns help to ensure the long-term survival of species. Some species have many, usually small, offspring and give them little or no parental care or protection. Examples include algae, bacteria, and most insects. These species reproduce at an early age and overcome typically massive losses of offspring by producing so many offspring that a few will likely survive to reproduce many more offspring and keep this reproductive pattern going. At the other extreme are species that tend to reproduce later in life and have a small number of offspring with longer life spans. Typically, the offspring of mammals with this reproductive strategy develop inside their mothers (where they are safe), and are born fairly large. After birth, they mature slowly and are cared for and protected by one or both parents, and in some cases by living in herds or groups, until they reach reproductive age and begin the cycle again. Most large mammals (such as elephants, whales, and humans) follow this reproductive pattern. Many of these species—especially those with long times between generations and with low reproductive rates, such as elephants, rhinoceroses, and sharks—are vulnerable to extinction. Most organisms have reproductive patterns between these two extremes.

Some Factors Can Limit Population Size

Different species and their populations thrive under different physical and chemical conditions. Some need bright sunlight; others flourish in shade. Some need a hot environment; others prefer a cool or cold one. Some do best under wet conditions; others thrive in dry conditions. Each population in an ecosystem has a range of tolerance to variations in its physical and chemical environment, as shown in Figure 5-15. Individuals within a population may also have slightly different tolerance ranges for temperature or other physical or chemical factors because of small differences in their genetic makeup, health, and age. For example, a trout population may do best within a narrow band of temperatures (optimum level or range), but a few individuals can survive above and below that band. Of course, if the water becomes much too hot or too cold, none of the trout can survive.

Human Population Growth Shows Certain Trends

Estimates of what the global human population is likely to be in 2050 range from 7.8 billion to 10.8 billion people, with a medium projection of 9.6 billion people. For the year 2100, the projected population size ranges from 8 billion to 16 billion (Figure 6-1). These varying estimates depend on a variety of factors that we consider in more detail later in this chapter. However, demographers, or population experts, recognize three important growth trends. First of all, in recent decades, the rate of population growth has slowed (Figure 6-2), but the world's population is still growing (Figure 6-1) at a rate of about 1.2%. This may not seem like much but in 2012 this growth added about 84 million people to the population—an average of more than 230,000 people each day, or almost 3 more people every second.

Family Planning Can Provide Several Benefits

Family planning provides educational and clinical services that help couples choose how many children to have and when to have them. Such programs vary from culture to culture, but most of them provide information on birth spacing, birth control, and health care for pregnant women and infants (Figure 6-18).

Populations Can Grow, Shrink, or Remain Stable

Four variables—births, deaths, immigration, and emigration—govern changes in population size. A population increases through birth and immigration (arrival of individuals from outside the population) and decreases through death and emigration (departure of individuals from the population): Population change = (Births + Immigration) - (Deaths + Emigration)

a. Human Population growth shows certain trends...(5)

Growth rate annually has dropped but population continues to grow 2. World's pop growth rate = 1.2% 3. Human growth unevenly distributed...mostly in more developed countries 4. pop growing exponentially in LDC 5. Most people move from rural to urban places

Humans Are Not Exempt from Nature's Population Controls

Humans are not exempt from population crashes. Ireland experienced such a crash after a fungus destroyed its potato crop in 1845. About 1 million people died from hunger or diseases related to malnutrition, and 3 million people migrated to other countries, especially the United States. During the 14th century, the bubonic plague spread through densely populated European cities and killed at least 25 million people. The bacterium causing this disease normally lives in rodents. It was transferred to humans by fleas that fed on infected rodents and then bit humans. The disease spread like wildfire through crowded cities, where sanitary conditions were poor and rats were abundant. Today, several antibiotics, not available until recently, can be used to treat bubonic plague. Currently, the world is experiencing a global epidemic of AIDS, caused by infection with the human immunodeficiency virus (HIV). Between 1981 and 2011, AIDS killed more than 30 million people and continues to claim another 1.7 million lives each year—an average of 3 deaths per minute.

In Some Interactions, Both Species Benefit

In mutualism, two species behave in ways that benefit both by providing each with food, shelter, or some other resource. One example is pollination of flowering plants by species such as honeybees, hummingbirds, and butterflies (see Chapter 4 opening photo) that feed on the nectar of flowers. Figure 5-9 shows an example of a mutualistic relationship that combines nutrition and protection. It involves birds that ride on the backs of large animals such as African buffalo, elephants, rhinoceroses, and impalas (Figure 5-9). The birds remove and eat parasites and pests (such as ticks and flies) from the animals' bodies and often make noises warning the larger animals when predators are approaching.

Several Factors Affect Birth Rates and Fertility Rate

Many factors affect a country's average birth rate and TFR. One is the importance of children as a part of the labor force, especially in less-developed countries. This is a major part of why it makes sense for many poor couples in those countries to have a large number of children. They need help with hauling daily drinking water (Figure 6-8), gathering wood for heating and cooking, and tending crops and livestock.

What Limits the Growth of Populations?

No population can grow indefinitely because of limitations on resources and because of competition among species for those resources.

Some Species Feed off Other Species by Living on or Inside Them

Parasitism occurs when one species (the parasite) feeds on another organism (the host), usually by living on or inside the host. In this relationship, the parasite benefits and the host is often harmed but not immediately killed. A parasite usually is much smaller than its host and rarely kills it. However, most parasites remain closely associated with their hosts, draw nourishment from them, and may gradually weaken them over time. Some parasites such as tapeworms live inside their hosts. Other parasites such as mistletoe plants and bloodsucking sea lampreys (Figure 5-8) attach themselves to the outsides of their hosts. Some parasites, including fleas and ticks, move from one host to another while others, such as tapeworms, spend their adult lives within a single host.

What Factors Influence the Size of the Human Population?

Population size increases through births and immigration, and decreases through deaths and emigration. The average number of children born to the women in a population (total fertility rate) is the key factor that determines population size.

Interactions between Predator and Prey Species Can Drive Each Other's Evolution

Predator and prey populations can exert intense natural selection pressures on one another. Over time, as a prey species develops traits that make it more difficult to catch, its predators face selection pressures that favor traits increasing their ability to catch their prey. Then the prey species must get better at eluding the more effective predators. When populations of two different species interact in such a way over a long period of time, changes in the gene pool of one species can lead to changes in the gene pool of the other. Such changes can help both competing species to become more competitive or to avoid or reduce competition. Biologists call this natural selection process coevolution.

The First Step Is to Promote Economic Development

Scientific studies and experience have shown that the three most effective ways to slow or stop population growth are to reduce poverty, primarily through economic development and universal primary education; to elevate the status of women; and to encourage family planning and reproductive health care (Concept 6-4). Let's begin by looking at the role of economic development. In the world's most desperately poor countries, couples tend to have more children for reasons listed earlier in this chapter. Thus, in many less-developed countries, total fertility and population growth rates tend to be high, and large numbers of poor people are increasingly being crowded into unsanitary and difficult living conditions in slums and shantytowns. Demographers, examining the birth and death rates of western European countries that became industrialized during the 19th century, have developed a hypothesis of population change known as the demographic transition: As countries become industrialized and economically developed, their populations tend to grow more slowly. According to the hypothesis, this transition takes place in four stages, as shown in Figure 6-16.

When a Population Exceeds Its Carrying Capacity It Can Crash

Some populations do not make a smooth transition from exponential growth to logistic growth. Instead, they use up their resource supplies and temporarily overshoot, or exceed, the carrying capacity of their environment. In such cases, the population suffers a sharp decline, called dieback, or population crash, unless part of the population can switch to new resources or move to an area that has more resources. Such a crash occurred when reindeer were introduced onto a small island in the Bering Sea (Figure 5-18).

No Population Can Grow Indefinitely: J-Curves and S-Curves

Some species have an incredible ability to increase their numbers. Members of such populations typically reproduce at an early age, have many offspring each time they reproduce, and reproduce many times, with short intervals between successive generations. For example, with no controls on its population growth, a species of bacteria that can reproduce every 20 minutes would generate enough offspring to form a 0.3-meter-deep (1-foot-deep) layer over the surface of the entire earth in only 36 hours—a dramatic illustration of the potential of exponential growth. Fortunately, this will not happen. Research reveals that regardless of their reproductive strategy, no population of a species can grow indefinitely because of limitations on resources and competition with populations of other species for those resources (Concept 5-2). In the real world, a rapidly growing population of any species eventually reaches some size limit imposed by one or more limiting factors such as the availability of light, water, temperature, space, or nutrients, or by exposure to predators or infectious diseases.

The Human Population Can Grow, Decline, or Remain Fairly Stable

The basics of global population change are quite simple. If there are more births than deaths during a given period of time, the earth's population increases, and when the opposite is true, it decreases. When the number of births equals the number of deaths during a particular time period, population size does not change. Instead of using the total numbers of births and deaths per year, demographers use the crude birth rate (the number of live births per 1,000 people in a population in a given year) and the crude death rate (the number of deaths per 1,000 people in a population in a given year).

How Do Environmental Scientists Think about Human Population Growth?

The continuing rapid growth of the human population and its impacts on natural capital raise questions about how long the human population can keep growing.

How Does a Population's Age Structure Affect Its Growth or Decline?

The numbers of males and females in young, middle, and older age groups determine how fast a population grows or declines.

Several Factors Affect Death Rates

The rapid growth of the world's population over the past 100 years is not primarily the result of a rise in the birth rate. Instead, it has been caused largely by declining death rates, especially in less-developed countries. More people in some of these countries are living longer and fewer infants are dying because of increased food supplies, improvements in food distribution, better nutrition, medical advances such as immunizations and antibiotics, improved sanitation, and safer water supplies. A useful indicator of the overall health of people in a country or region is life expectancy, which for any given year is the average number of years a person born in that year can be expected to live. Between 1955 and 2012, the average global life expectancy increased from 48 years to 70 years. In 2012, Japan had the world's longest life expectancy of 83 years. In the world's poorest countries, life expectancy is 55 years or less.

How Do Communities and Ecosystems Respond to Changing Environmental Conditions?

The structure and species composition of communities and ecosystems change in response to changing environmental conditions through a process called ecological succession.

Migration Affects an Area's Population Size

The third factor in population change is migration: the movement of people into (immigration) and out of (emigration) specific geographic areas. Most people migrating from one area or country to another seek jobs and economic improvement. But many are driven to migrate by religious persecution, ethnic conflicts, political oppression, or war.

Communities and Ecosystems Change over Time: Ecological Succession

The types and numbers of species in biological communities and ecosystems change in response to changing environmental conditions such as a fires, volcanic eruptions, climate change, and the clearing of forests to plant crops. The normally gradual change in species composition in a given area is called ecological succession (Concept 5-3). Ecologists recognize two main types of ecological succession, depending on the conditions present at the beginning of the process. Primary ecological succession involves the gradual establishment of communities of different species in lifeless areas where there is no soil in a terrestrial ecosystem or no bottom sediment in an aquatic ecosystem. Examples include bare rock exposed by a retreating glacier (Figure 5-11), newly cooled lava, an abandoned highway or parking lot, and a newly created shallow pond or reservoir. Primary succession usually takes hundreds to thousands of years because of the need to build up fertile soil or aquatic sediments to provide the nutrients needed to establish a plant community.

How Can We Slow Human Population Growth?

We can slow human population growth by reducing poverty, elevating the status of women, and encouraging family planning.

what is ecological niche?

each species plays a role in its ecosystem

most common interactions among species is....

interspecific competition - occurs when 2 or more members of species interact to use the same limited resources while fighting for resources improves their efficiency to survive

what is resource partitioning?

some species evolve ways to share resources (3 ways)

what is predation?

when one species feeds on another