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Applying Population Ecology: The Human Population

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1 Applying Population Ecology: The Human Population
G. Tyler Miller’s Living in the Environment 14th Edition Chapter 9 Applying Population Ecology: The Human Population Chapter 10

2 Chapter 9 Key Concepts – Population Ecology
Factors affecting population size Species reproductive patterns Species survivorship patterns Conservation biology and human impacts on ecosystems Population Dynamics and Carrying Capacity Population dynamics Biotic potential (intrinsic rate of increase [rmax]) Environmental resistance Carrying capacity Exponential and Logistic Growth Population Density

3 The Study of Population Dynamics
Populations change in size, density, dispersion and age structure. Population density —the number of individuals of a population that inhabit a certain unit of land or water area. Population dispersion —refers to how individuals of a population are spaced within a region. Age structure of a population is usually described as the pre-reproductive stage, the reproductive stage and the post-reproductive stage. A population with a large reproductive stage is likely to increase, while a population with a large post-reproductive stage is likely to decrease.

4 Population Size Four variables influence/govern population size: (1) births, (2) deaths, (3) immigration, and (4) emigration. Increase in population occurs by birth and immigration. Decrease in population occurs by death and emigration. Rapidly growing populations have four characteristics: Individuals in the population reproduce early in life. Individuals have short periods between generations. Individuals have long reproductive lives. Individuals produce multiple offspring each time they reproduce.

5 Biotic Potential vs. Environmental Resistance
The biotic potential max (rmax) is the population's capacity for growth. The intrinsic rate of increase (r) is the rate of population growth with unlimited resources. environmental resistance consists of factors that limit population growth. limiting Factors No population can grow indefinitely due to limited resources such as light, water, and nutrients and also due to competitors and/or predators.

6 Limiting Factors Examples:
Extrinsic Biotic – Density Dependent Abiotic – Density Independent Intrinsic Social Hierarchy Gender changing Density-independent population controls affect a population's size regardless of its density. These are abiotic factors in the community. Density-dependent factors or population controls have a greater affect on the population as its density increases. Infectious disease is an example of density-dependent population control.

7 Environmental resistance
Biotic Potential v. Environmental Resistance (Logistic Population Growth) Carrying capacity (K) is determined by biotic potential and environmental resistance. (K) is is the number of a species individuals that can be sustained indefinitely in a specific space. As a population reaches its carrying capacity, its growth rate will decrease because resources become more scarce. Environmental resistance Carrying capacity (K) Population size (N) Biotic potential Exponential growth Figure 9-4 Page 166 Time (t)

8 Natural Population Curves
Population sizes may stay about the same, suddenly increase and then decrease, vary in regular cycles, or change erratically. Four general types of population fluctuations in nature are (1) stable, (2) irruptive, (3) cyclic, and (4) irregular. A stable population fluctuates slightly above and below carrying capacity and is characteristic of many species Living under fairly constant environmental conditions. Fig. 9-7 p. 168 Some species have a fairly stable population size That may occasionally irrupt to a high peak and then crash to below carrying capacity. This is characteristic of short-lived, rapidly reproducing species. Cyclic fluctuations occur over a regular time period, generally a multiple year cycle. Irregular behavior is poorly understood. Some scientists attribute irregular behavior to chaos in the system; others disagree.

9 Exponential and Logistic Growth

10 The Role of Predation in Controlling Population Size
Interactions between predators and their prey change in cycles and appear to be caused by species interactions, but other factors may be involved. The hypothesis of top-down control of prey by predators may not be the only explanation for the boom-and-bust cycles seen in these populations. This may also be related to the food supply of prey. The bottom-up control hypothesis states that plants are consumed too rapidly by prey for replacement to keep up. This may lead to a crash of herbivores, and that may lead to a crash of higher predators. Fig. 9-8 p. 168 These are not mutually exclusive hypotheses; more probably have interaction between predation and food supplies.

11 Population dispersion
Fig. 9-2 p. 164 clumping dispersion the most common dispersion pattern for populations. In this type of dispersion, individuals "flock together.“ uniform dispersion a type of population dispersion in which the members of the population are uniformly spaced throughout their geographic region. random dispersion a type of population dispersion in which the position of each individual is not determined or influenced by the other members of the population. Most species live in clumps or groups; reasons may include: Availability of resources varies from place to place. Living in groups offers better protection from predators. Some predator species live in packs to better have a chance to get a meal. Temporary groups may form for mating and caring for young. Uniform pattern distribution may occur where a resource, such as water, is scarce.

12 Reproductive Patterns and Survival
Some species reproduce without having sex, and others reproduce by having sex. Asexual reproduction does not utilize sex; each cell can divide and produce two identical cells that are replicas of the original cell. Sexual reproduction occurs when gametes from each parent combine to produce offspring with a combination of genetic traits from each parent. Three disadvantages to sexual reproduction: Males do not give birth; females have to produce twice the offspring to maintain the same number of young as an asexual organism. Chance of genetic errors/defects increase during splitting and recombination. Courtship/mating consume energy and time, transmit disease, and inflict injury on males in some cases Two important advantages are genetic diversity for survival of species in the face of changes in environment and males may help with food gathering and/or rearing of young.

13 Reproductive Patterns and Survival
Fig p. 170 Reproductive patterns can be classified into two fundamental reproductive patterns: r-selected and K-selected species. Availability of a suitable habitat for individuals of a population ultimately determines the population size.

14 Reproductive Strategies
r-Selected species are opportunists and reproduce when conditions are favorable or when disturbance opens a niche for invasion. Most species of this type go through irregular and unstable boom-and-bust cycles in population size. K-selected species generally follow a logistic growth curve. Many of the larger species with long generation times and a low reproductive rate are prone to extinction.

15 Survivorship Curves Populations of different species vary in how long individual members typically live. A survivorship curve is one way to represent age structure of a population. Three generalized types of survivorship curves are: late loss, early loss, and constant loss. A life table shows the numbers of individuals at each age on a survivorship curve. Insurance companies use life tables to determine the cost of insurance policies. Fig p. 171

16 Effects of Genetic Variations on Population Size
Variations in genetic diversity can affect the survival of small, isolated populations. Several factors can play a role in loss of genetic diversity and survival of a small population. The founder effect is when a few individuals move to a new location that is isolated from the original population. There is limited genetic diversity in such a population. A demographic bottleneck occurs when only a few individuals survive a catastrophe. Genetic drift is a third factor and involves random changes in gene frequencies in a population. This may help or hurt the survival of the population. Inbreeding occurs when members of a small population mate one another; this may increase the numbers of defective genes in a population. Metapopulations occur where some mobile populations occasionally exchange genes when some members get together. Conservation biologists use this information to establish migration routes that will enhance population size, genetic diversity, and survival of related local populations.

17 Human Impacts on Ecosystems
Habitat degradation and fragmentation Humans have altered nature in ways that threaten the survival of many species, including our own species. Humans have directly affected changes on about 83% of the earth's land surface. Ecosystem simplification Genetic resistance Predator elimination Introduction of non-native species Overharvesting renewable resources Interference with ecological systems

18 Human Impacts on Ecosystems
Humans have altered nature to meet needs and wants in nine major ways. 1. Destruction, fragmentation, and degrading of wildlife habitats have reduced biodiversity. 2. The simplification and homogenization of natural ecosystems by clearing land and planting a single species (monoculture) reduces numbers of species and interactions. Opportunistic species and pest organisms are costing time, energy, and money to control. Invasion of pathogenic organisms is another threat. 3. Destruction of the earth's net primary productivity is a third type of alteration. 4. Certain types of intervention have unintentionally strengthened pest species and disease-causing bacteria. 5. Some predator species have been deliberately eliminated from ranching areas. 6. Alterations have occurred due to the introduction of nonnative (invasive) or new species into an ecosystem.

19 Human Impacts on Ecosystems
7. A number of renewable resources have been over-harvested, such as overgrazing of grasslands, over-hunting of wildlife, and pumping out aquifers for freshwater faster than they can recharge. 8. Some human activities also interfere with normal chemical cycling and energy flows in ecosystems 9. Human-dominated ecosystems are increasingly dependent on nonrenewable energy from fossil fuels that produce pollution and add greenhouse gases to the atmosphere. Alteration of natural ecosystems needs to be slowed down, and we need to maintain a balance between simplified, human-altered ecosystems and more complex, natural ecosystems

20 Learning from Nature Dependence on Nature Interdependence Unpredictability Limited resources Recycle wastes See Connections p. 173

21 Learning from Nature By mimicking four major ways
that nature has adapted and sustained itself, we can develop more sustainable economies. We are totally dependent on the sun and Earth for life. We are an expendable species. Everything is interconnected and interdependent. What connections are strongest, most important, and most vulnerable are those that we must discover. Any intrusion into nature has unexpected and unintended side effects. We must not deplete and degrade the earth's natural capital.

22 Principles of Sustainability
Solutions Principles of Sustainability How Nature Works Lessons for Us Rely mostly on renewable solar energy. Prevent and reduce pollution and recycle and reuse resources. Preserve biodiversity by protecting ecosystem services and preventing premature extinction of species. Reduce births and wasteful resource use to prevent environmental overload and depletion and degradation of resources. Runs on renewable solar energy. Recycles nutrients and wastes. There is little waste in nature. Uses biodiversity to maintain itself and adapt to new environmental conditions. Controls a species population size and resource use by interactions with its environment and other species. Figure 9-15 Page 174

23 Applying Population Ecology: The Human Population Chapter 10
Key Concepts Factors affecting human population size Human population problems Managing population growth

24 Factors Affecting Human Population Size
Demography is the study of the size, composition, and distribution of human populations and the causes and consequences of changes in these characteristics. Population change equation Population Change = (Births + Immigration) – (Deaths + Emigration) Crude birth rate (BR) The crude birth rate is the number of live births per 1,000 people in a population in a specific year.| Crude death rate (DR) The crude death rate is the number of deaths per 1,000 people in a population in a specific year

25 Describing Population Changes
Doubling Times “Rule of 70”: Doubling time is one measure of population growth. Fertility-is the number of births that occur to an individual woman in a population. Replacement-level Fertility —the number of children a couple must have in order to replace themselves in a population. Total Fertility Rate (TFR) —the number of children a woman will bear during her lifetime; this information is based on an analysis of data from preceding years in the population in question. Who is Over Populated?

26 Factors Affecting Human Population Size (2005 Data)
There are currently more births than deaths throughout the world. 1. The annual rate of natural population change (%) equals birth rate minus death rate divided by 1,000 persons multiplied by 100. 2. The rate of the world's population growth has decreased. The annual population growth dropped by almost half between 1963 and 2004, from 2.2% to 1.2%. But during this same period, the population base doubled from 3.2 to 6.4 billion. There is a big difference in the exponential population growth rates of developed and developing countries, with developed countries growing at 0.25% and developing countries growing at 1.46%— almost six times faster. The six fastest growing countries in terms of population are: India, China, Pakistan, Nigeria, Bangladesh, and Indonesia. The populations of China and India comprise 38% of the world's population. The next most populated country is the United Stated with 4.6% of the world's population.

27 Factors Affecting Birth Rates and Total Fertility Rates
Many factors influence birth and fertility rates. More children work in developing countries; they are important to the labor force. The economic cost of raising and educating children determines their numbers. The more children cost, the less children people tend to have. If there are available private/public pension systems, adults have fewer children because they don't need children to take care of them in old age. People in urban areas usually have better access to family planning, so they have fewer children.

28 If women have educational and economic choices, they tend to have fewer children.
When the infant mortality rate is low, people have fewer children because children are not being lost to death. The older the age at which women marry, the fewer children they bear. If abortions are available and legal, women have fewer children. The availability of reliable birth control allows women to space children and determine the number of children they bear.

29 Births per thousand population
U.S. Birth Rates: Fig. 10-8, p. 180 32 30 28 26 Births per thousand population 24 22 20 Demographic transition End of World War II 18 Depression 16 Baby boom Baby bust Echo baby boom 14 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 Year From , the United States had a sharp rise in birth rate, called the baby-boom period. At its peak, the TFR reached 3.7 children per woman. There has been a gradual decline since then. The population growth of the United States is still greater than any other developed country and is not close to leveling off.

30 Factors Affecting Human Population Size
About 2.7 million people were added to the U.S. population in Fifty-five percent of this population growth came from more births than deaths, and forty-five percent came from immigration. Other major developed countries have slower population growth, and most are expected to have declining populations after 2010 The high U.S. per capita resource rate use produces enormous environmental impact.

31 Immigration Policy Arguments to limit immigration into the U.S.
Limitations would aid in stabilizing the population sooner. Limitations would help reduce the enormous environmental impact of the U.S. Arguments for generous immigration policies in the U.S. Historically, the U.S. has been the land of opportunity for the world's poor. Immigrants do work that Americans won't do or handle jobs for which there are not enough trained natives. Immigrants contribute to the economy and pay taxes.

32 Factors Affecting Human Population Size
Factors, which have caused a decline in death rates, are the following: Better food supplies and nutrition and safer water supplies contribute to people living longer. Advances in medicine and public health and improved sanitation and personal hygiene also contribute to people living longer. Life expectancy is the average number of years a newborn can expect to live. Infant mortality rate (IMR) is the number of babies out of every 1,000 born who die before their first birthday. a. This rate reflects a country's level of nutrition and health care. b. It is the single best measure of a society's quality of life. U.S. infant mortality rate is higher than 35 other countries due to: a. inadequate health care for poor women and for their babies, b. drug addiction among pregnant women, and c. a high birth rate among teenagers.

33 Population Age Structure
Rapid Growth Guatemala Nigeria Saudi Arabia Slow Growth United States Australia Canada Male Female Zero Growth Spain Austria Greece Negative Growth Germany Bulgaria Sweden Fig p. 184

34 Global Aging

35 Relative population size Birth rate and death rate
The Demographic Transition Fig p. 189 Low High Relative population size (number per 1,000 per year) Birth rate and death rate 80 70 60 50 40 30 20 10 Stage 1 Preindustrial Stage 2 Transindustrial Stage 3 Industrial Stage 4 Postindustrial growth rate Increasing Growth Very high Decreasing Zero Negative Birth rate Total population Death rate Time

36 Solutions: Influencing Population Size
Migration Environmental refugees Reducing births Family planning Empowerment of women Economic rewards and penalties

37 Case Study: Slowing Population Growth in India
Generally disappointing results: Poor planning Bureaucratic inefficiency Low status of women Extreme poverty Lack of support World in the Balance - India

38 Case Study: Slowing Population Growth in China
Economic incentives Free medical care Preferential treatment Locally administered Very intrusive and coercive World in the Balance - China

39 Population Growth in Sub-Saharan Africa
How do different populations compare? Sub-Saharan Africa

40 Cutting Global Population Growth
Family planning Improve health care Elevate the status of women Increase education Involve men in parenting Reduce poverty Sustainability

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