Chapter 52 (pgs. 1151- 1172) Population Ecology AP minknow How density, dispersion, and demographics can describe a population. The differences between exponential and logistic models of population growth. How density-dependent and density-independent factors can control population growth

Characteristics of Populations 1.Define the scope of population ecology  2.Define and distinguish between density and dispersion.  3.Explain how ecologists measure the density of a species.  4.Describe conditions that may result in the clumped dispersion, uniform dispersion, and random dispersion of populations.  5.Describe the characteristics of populations that exhibit Type I, Type II, and Type III survivorship curves.   6.Describe the characteristics of populations that exhibit Type I, Type II, and Type III survivorship curves. Life History Traits 7.Define and distinguish between semelparity and iteroparity.  8.Explain how limited resources affect life histories.  9.Give examples of the trade-off between reproduction and survival.

Population Growth 10.Compare the geometric model of population growth with the logistic model.   11.Explain how an environment's carrying capacity affects the intrinsic rate of increase of a population.  12.Distinguish between r-selected populations and K-selected populations.  13.Explain how a "stressful" environment may alter the standard r-selection and K-selection characteristics. Population-Limiting Factors 14.Explain how density-dependent factors affect population growth.  15.Explain how density-dependent and density-independent factors may work together to control a population's growth.  16.Explain how predation can affect life history through natural selection.  17.Describe several boom-and-bust population cycles, noting possible causes and consequences of the fluctuations. Human Population Growth 18.Describe the history of human population growth.  19.Define the demographic transition.  20.Compare the age structures of Italy, Kenya, and the United States. Describe the possible consequences for each country.  21.Describe the problems associated with estimating Earth's carrying capacity.

Population ecology is the study of populations in relation to environment Including environmental influences on population density and distribution, age structure, and variations in population size

52.1: Dynamic biological processes influence population density, dispersion, and demography A population A population Is a group of individuals of a single species living in the same general area

Density and Dispersion Is the number of individuals per unit area or volume Dispersion Is the pattern of spacing among individuals within the boundaries of the population

Density: A dynamic perspective. Births and immigration add individuals to a population. Births Immigration PopuIation size Emigration Deaths Deaths and emigration remove individuals from a population. Determining the density of natural populations Is possible, but difficult to accomplish In most cases It is impractical or impossible to count all individuals in a population Density is the result of a dynamic interplay Between processes that add individuals to a population and those that remove individuals from it

Patterns of Dispersion Environmental and social factors Influence the spacing of individuals in a population. There are three different Patterns of Dispersion Clumped Dispersion Uniform Dispersion Random Dispersion

A clumped dispersion Is one in which individuals aggregate in patches May be influenced by resource availability and behavior Figure 52.3a (a) Clumped. For many animals, such as these wolves, living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young, and helps exclude other individuals from their territory.

A uniform dispersion Is one in which individuals are evenly distributed May be influenced by social interactions such as territoriality Figure 52.3b (b) Uniform. Birds nesting on small islands, such as these king penguins on South Georgia Island in the South Atlantic Ocean, often exhibit uniform spacing, maintained by aggressive interactions between neighbors.

A random dispersion Is one in which the position of each individual is independent of other individuals Figure 52.3c (c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

Life Tables A life table Is an age-specific summary of the survival pattern of a population Is best constructed by following the fate of a cohort

Survivorship Curves A survivorship curve Is a graphic way of representing the data in a life table Figure 52.4 1000 100 10 1 Number of survivors (log scale) 2 4 6 8 Age (years) Males Females

Survivorship curves can be classified into three general types Type I, Type II, and Type III I II III 50 100 1 10 1,000 Percentage of maximum life span Number of survivors (log scale) Many species fall somewhere between these basic types of survivorship curves. Some invertebrates, such as crabs, show a “stair-stepped” curve, with increased mortality during molts. Figure 52.5

52.2 Life histories are highly diverse, but they exhibit patterns in their variability. Life histories entail three basic variables: when reproduction begins how often the organism reproduces how many offspring are produced during each reproductive episode. These histories are evolutionary outcomes reflected in the development, physiology, and behavior of an organism. Some organisms, such as the agave plant, exhibit semelparity. Big Bang Production. (then death) By contrast, some organisms exhibit iteroparity. They produce only a few offspring during repeated reproductive episodes.

Some plants produce a large number of small seeds Ensuring that at least some of them will grow and eventually reproduce Figure 52.8a (a) Most weedy plants, such as this dandelion, grow quickly and produce a large number of seeds, ensuring that at least some will grow into plants and eventually produce seeds themselves.

Other types of plants produce a moderate number of large seeds That provide a large store of energy that will help seedlings become established Figure 52.8b (b) Some plants, such as this coconut palm, produce a moderate number of very large seeds. The large endosperm provides nutrients for the embryo, an adaptation that helps ensure the success of a relatively large fraction of offspring.

What factors contribute to the evolution of semelparity versus iteroparity? In other words, how much does an individual gain in reproductive success through one pattern versus the other? The critical factor is survival rate of the offspring. When the survival of offspring is low, as in highly variable or unpredictable environments, big-bang reproduction (semelparity) is favored. Repeated reproduction (iteroparity) is favored in dependable environments where competition for resources is intense. In such environments, a few, well-provisioned offspring have a better chance of surviving to reproductive age.

Population Growth is measured by Per Capita Rate of Increase If immigration and emigration are ignored A population’s growth rate (per capita increase) equals birth rate minus death rate Growth rate = rN It can be found using the equation--- dN dt  rN

Exponential Population Growth Is population increase under idealized conditions Under these conditions The rate of reproduction is at its maximum, called the intrinsic rate of increase Exponential population growth Results in a J-shaped curve Figure 52.9 5 10 15 500 1,000 1,500 2,000 Number of generations Population size (N) dN dt  1.0N 0.5N dN dt  rmaxN

The J-shaped curve of exponential growth Is characteristic of some populations that are rebounding Figure 52.10 1900 1920 1940 1960 1980 Year 2,000 4,000 6,000 8,000 Elephant population

52.4: The logistic growth model includes the concept of carrying capacity Exponential growth Cannot be sustained for long in any population A more realistic population model Limits growth by incorporating carrying capacity Carrying capacity (K) Is the maximum population size the environment can support

The Logistic Growth Model In the logistic population growth model The per capita rate of increase declines as carrying capacity is reached We construct the logistic model by starting with the exponential model And adding an expression that reduces the per capita rate of increase as N increases Maximum Positive Negative N  K Population size (N) Per capita rate of increase (r)

The logistic growth equation Table 52.3 Includes K, the carrying capacity dN dt  (K  N) K rmax N

The logistic model of population growth Produces a sigmoid (S-shaped) curve dN dt  1.0N Exponential growth Logistic growth 1,500  N 1,500 K  1,500 5 10 15 500 1,000 2,000 Number of generations Population size (N) Figure 52.12

As N approaches K for a certain population, which of the following is predicted by the logistic equation? The growth rate will not change. The growth rate will approach zero. The population will show an Allee effect. The population will increase exponentially. The carrying capacity of the environment will increase. Answer: b Source: Barstow - Test Bank for Biology, Sixth Edition, Question #29.

The Logistic Model and Real Populations 800 600 400 200 Time (days) 5 10 15 1,000 Number of Paramecium/ml The growth of laboratory populations of paramecia Fits an S-shaped curve Some populations overshoot K Before settling down to a relatively stable density Some populations Fluctuate greatly around K 180 150 120 90 60 30 Time (days) 160 140 80 100 40 20 Number of Daphnia/50 ml 80 60 40 20 1975 1980 1985 1990 1995 2000 Time (years) Number of females

The Logistic Model and Life Histories Life history traits favored by natural selection May vary with population density and environmental conditions K-selection, or density-dependent selection Selects for life history traits that are sensitive to population density K-selection tends to maximize population size and operates in populations living at a density near K. r-selection, or density-independent selection Selects for life history traits that maximize reproduction r-selection tends to maximize r, the rate of increase, and occurs in environments in which population densities fluctuate well below K, or when individuals face little competition. Controversy

Density-dependent birth rate 52.5: Populations are regulated by a complex interaction of biotic and abiotic influences In density-independent populations Birth rate and death rate do not change with population density In density-dependent populations Birth rates fall and death rates rise with population density Determining equilibrium for population density Figure 52.14a–c Density-dependent birth rate Density-dependent death rate Equilibrium density Density-independent death rate Density-independent birth rate Population density Birth or death rate per capita (a) Both birth rate and death rate change with population density. (b) Birth rate changes with population density while death rate is constant. (c) Death rate changes with population density while birht rate is constant.

Density-Dependent Population Regulation Density-dependent birth and death rates Are an example of negative feedback that regulates population growth Are affected by many different mechanisms Competition for Resources Territoriality Health (Disease/Parasites) Predation Toxic Wastes (think bacteria)

Competition for Resources In crowded populations, increasing population density Intensifies intraspecific competition for resources 10 100 1,000 10,000 Average number of seeds per reproducing individual (log scale) Average clutch size Seeds planted per m2 Density of females 70 20 30 40 50 60 80 2.8 3.0 3.2 3.4 3.6 3.8 4.0 (a) Plantain. The number of seeds produced by plantain (Plantago major) decreases as density increases. (b) Song sparrow. Clutch size in the song sparrow on Mandarte Island, British Columbia, decreases as density increases and food is in short supply.

Territoriality Cheetahs are highly territorial Using chemical communication to warn other cheetahs of their boundaries Figure 52.16

Population Dynamics The study of population dynamics Focuses on the complex interactions between biotic and abiotic factors that cause variation in population size

Stability and Fluctuation Long-term population studies Have challenged the hypothesis that populations of large mammals are relatively stable over time Figure 52.18 The pattern of population dynamics observed in this isolated population indicates that various biotic and abiotic factors can result in dramatic fluctuations over time in a moose population. Researchers regularly surveyed the population of moose on Isle Royale, Michigan, from 1960 to 2003. During that time, the lake never froze over, and so the moose population was isolated from the effects of immigration and emigration. FIELD STUDY Over 43 years, this population experienced two significant increases and collapses, as well as several less severe fluctuations in size. RESULTS CONCLUSION 1960 1970 1980 1990 2000 Year Moose population size 500 1,000 1,500 2,000 2,500 Steady decline probably caused largely by wolf predation Dramatic collapse caused by severe winter weather and food shortage, leading to starvation of more than 75% of the population

Commercial catch (kg) of male crabs (log scale) Extreme fluctuations in population size Are typically more common in invertebrates than in large mammals Figure 52.19 1950 1960 1970 1980 Year 1990 10,000 100,000 730,000 Commercial catch (kg) of male crabs (log scale) Fluctuating Wind pushing eggs out to sea Cannibalism

Metapopulations and Immigration Are groups of populations linked by immigration and emigration High levels of immigration combined with higher survival Can result in greater stability in populations Mandarte island Small islands Number of breeding females 1988 1989 1990 1991 Year 10 20 30 40 50 60

Population Cycles Many populations Undergo regular boom-and-bust cycles Figure 52.21 Year 1850 1875 1900 1925 40 80 120 160 3 6 9 Lynx population size (thousands) Hare population size (thousands) Lynx Snowshoe hare Three main hypotheses have been proposed to explain the lynx/hare cycles. The cycles may be caused by food shortage during winter. The cycles may be due to predator-prey interactions. The cycles may be affected by a combination of food resource limitation and excessive predation.

Limiting Factors Density Dependant Factors Density Independent Factors

No population can grow indefinitely 52.6: Human population growth has slowed after centuries of exponential increase No population can grow indefinitely And humans are no exception The Global Human Population 8000 B.C. 4000 B.C. 3000 B.C. 2000 B.C. 1000 B.C. 1000 A.D. The Plague Human population (billions) 2000 A.D. 1 2 3 4 5 6 Increased relatively slowly until about 1650 and then began to grow exponentially

Global population Growth Rate Though the global population is still growing The rate of growth began to slow approximately 40 years ago Figure 52.23 1950 1975 2000 2025 2050 Year 2003 Percent increase 2.2 2 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 1.8

Age Structure One important demographic factor in present and future growth trends Is a country’s age structure, the relative number of individuals at each age Usually presented in Pyramids Figure 52.25 Rapid growth Afghanistan Slow growth United States Decrease Italy Male Female Age 8 6 4 2 Percent of population 80–84 85 75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 20–24 25–29 10–14 5–9 0–4 15–19

Infant Mortality and Life Expectancy Infant mortality and life expectancy at birth Vary widely among developed and developing countries but do not capture the wide range of the human condition Figure 52.26 Developed countries Developing countries Infant mortality (deaths per 1,000 births) Life expectancy (years) 60 50 40 30 20 10 80

Global Carrying Capacity Just how many humans can the biosphere support? It is complex and we just don’t know, but we have….

Ecological Footprint The ecological footprint concept Figure 52.27 16 14 12 10 8 6 4 2 New Zealand Australia Canada Sweden World China India Available ecological capacity (ha per person) Spain UK Japan Germany Netherlands Norway USA Ecological footprint (ha per person) The ecological footprint concept Summarizes the aggregate land and water area needed to sustain the people of a nation Is one measure of how close we are to the carrying capacity of Earth At more than 6 billion people The world is already in ecological deficit