Chapter 36 Population Ecology

Populations are described by their boundaries and size Population ecology is the study of populations in relation to their environment, including environmental influences on density and distribution, age structure, and population size A population is a group of individuals of a single species living in the same general area Populations are described by their boundaries and size © 2011 Pearson Education, Inc.

Density and Dispersion Density is the number of individuals per unit area or volume Dispersion is the pattern of spacing among individuals within the boundaries of the population © 2011 Pearson Education, Inc.

Density: A Dynamic Perspective In most cases, it is impractical or impossible to count all individuals in a population Immigration is the influx of new individuals from other areas Emigration is the movement of individuals out of a population Sampling techniques - Population size can be estimated by either extrapolation from small samples, an index of population size (e.g., number of nests), or the mark-recapture method © 2011 Pearson Education, Inc.

Deaths and emigration remove individuals from a population. Figure 53.3 Births Deaths Deaths and emigration remove individuals from a population. Births and immigration add individuals to a population. Figure 53.3 Population dynamics. Immigration Emigration 5

Patterns of Dispersion Figure 53.4 (a) Clumped Patterns of Dispersion (b) Uniform Figure 53.4 Patterns of dispersion within a population’s geographic range. (c) Random 6

Most organisms exhibit a clumped dispersion pattern (i. e Most organisms exhibit a clumped dispersion pattern (i.e. herds, packs, etc). © 2011 Pearson Education, Inc.

Figure 53.4a (a) Clumped Figure 53.4 Patterns of dispersion within a population’s geographic range. 8

A uniform dispersion is one in which individuals are evenly distributed It may be influenced by social interactions such as territoriality, the defense of a bounded space against other individuals Plants – secrete toxins into soil to prevent growth of neighboring plants within a certain distance. (ie. Sage plant) © 2011 Pearson Education, Inc.

Figure 53.4b (b) Uniform Figure 53.4 Patterns of dispersion within a population’s geographic range. 10

It occurs in the absence of strong attractions or repulsions In a random dispersion, the position of each individual is independent of other individuals It occurs in the absence of strong attractions or repulsions © 2011 Pearson Education, Inc.

Figure 53.4c (c) Random Figure 53.4 Patterns of dispersion within a population’s geographic range. 12

Demographics Demography is the study of the vital statistics of a population and how they change over time Death rates and birth rates are of particular interest to demographers © 2011 Pearson Education, Inc.

Table 53.1 Table 53.1 Life Table for Belding’s Ground Squirrels (Spermophilus beldingi) at Tioga Pass, in the Sierra Nevada of California 14

Survivorship Curves A survivorship curve is a graphic way of representing the data in a life table The survivorship curve for Belding’s ground squirrels shows a relatively constant death rate © 2011 Pearson Education, Inc.

Number of survivors (log scale) Figure 53.5 1,000 100 Number of survivors (log scale) Females 10 Males Figure 53.5 Survivorship curves for male and female Belding’s ground squirrels. 1 2 4 6 8 10 Age (years) 16

3 Types of Survivorship Curves: Type I: low death rates during early and middle life and an increase in death rates among older age groups Type II: a constant death rate over the organism’s life span Type III: high death rates for the young and a lower death rate for survivors Many species are intermediate to these curves © 2011 Pearson Education, Inc.

Number of survivors (log scale) Figure 53.6 1,000 I 100 II Number of survivors (log scale) 10 Figure 53.6 Idealized survivorship curves: Types I, II, and III. III 1 50 100 Percentage of maximum life span 18

Measuring Population Growth Rates Change in population size Births Immigrants entering Deaths Emigrants leaving    For measuring GLOBAL changes - immigration and emigration are ignored, a population’s growth rate equals birth rate minus death rate ONLY! © 2011 Pearson Education, Inc.

Exponential Growth Model Exponential population growth is population increase under idealized condition Idealized situations help us understand the capacity of species to increase and the conditions that may facilitate this growth Exponential population growth results in a J-shaped curve © 2011 Pearson Education, Inc.

2,000 dN dt = 1.0N 1,500 dN dt = 0.5N Population size (N) 1,000 500 5 Figure 53.7 2,000 dN dt = 1.0N 1,500 dN dt = 0.5N Population size (N) 1,000 500 Figure 53.7 Population growth predicted by the exponential model. 5 10 15 Number of generations 21

Figure 53.8 8,000 6,000 Elephant population 4,000 2,000 Figure 53.8 Exponential growth in the African elephant population of Kruger National Park, South Africa. 1900 1910 1920 1930 1940 1950 1960 1970 Year The elephant population in Kruger National Park, South Africa, grew exponentially after hunting was banned 22

Exponential growth cannot be sustained for long in any population The logistic model describes how a population grows more slowly as it nears its 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 Carrying capacity varies with the abundance of limiting resources © 2011 Pearson Education, Inc.

The Logistic Growth Model In the logistic population growth model, the per capita rate of increase declines as carrying capacity is reached The logistic model of population growth produces a sigmoid (S-shaped) curve © 2011 Pearson Education, Inc.

( ) Exponential growth 2,000 dN dt = 1.0N 1,500 K = 1,500 Figure 53.9 Exponential growth 2,000 dN dt = 1.0N 1,500 K = 1,500 Logistic growth dN dt ( 1,500 – N 1,500 ) Population size (N) = 1.0N 1,000 Figure 53.9 Population growth predicted by the logistic model. Population growth begins slowing here. 500 5 10 15 Number of generations 27

Number of Paramecium/mL Figure 53.10 1,000 180 150 800 Number of Daphnia/50 mL 120 Number of Paramecium/mL 600 90 400 60 200 30 5 10 15 20 40 60 80 100 120 140 160 Figure 53.10 How well do these populations fit the logistic growth model? Time (days) Time (days) (a) A Paramecium population in the lab (b) A Daphnia population in the lab 28

Many factors that regulate population growth are density dependent There are two general questions about regulation of population growth What environmental factors stop a population from growing indefinitely? Why do some populations show radical fluctuations in size over time, while others remain stable? © 2011 Pearson Education, Inc.

Mechanisms of Density-Dependent Population Regulation Density-dependent birth and death rates are an example of negative feedback that regulates population growth Density-dependent birth and death rates are affected by many factors, such as competition for resources, territoriality, disease, predation, toxic wastes, and intrinsic factors © 2011 Pearson Education, Inc.

Density-Dependent Controls Competition for resources Predation Parasitism Disease

Competition for Resources In crowded populations, increasing population density intensifies competition for resources and results in a lower birth rate © 2011 Pearson Education, Inc.

Toxic Wastes Accumulation of toxic wastes can contribute to density-dependent regulation of population size © 2011 Pearson Education, Inc.

Predation As a prey population builds up, predators may feed preferentially on that species © 2011 Pearson Education, Inc. © 2011 Pearson Education, Inc.

Intrinsic Factors For some populations, intrinsic (physiological) factors appear to regulate population size © 2011 Pearson Education, Inc.

Territoriality In many vertebrates and some invertebrates, competition for territory may limit density © 2011 Pearson Education, Inc.

Disease Population density can influence the health and survival of organisms In dense populations, pathogens can spread more rapidly © 2011 Pearson Education, Inc.

Figure 53.17f Figure 53.17 Exploring: Mechanisms of Density-Dependent Regulation 38

Density-Independent Controls Natural disasters Severe weather Pollution Pesticide spraying

Population Cycles: Scientific Inquiry Some populations undergo regular boom-and-bust cycles Lynx populations follow the 10-year boom-and-bust cycle of hare populations © 2011 Pearson Education, Inc.

Number of hares (thousands) Number of lynx (thousands) Figure 53.19 Snowshoe hare 160 120 80 40 9 6 3 Number of hares (thousands) Lynx Number of lynx (thousands) Figure 53.19 Population cycles in the snowshoe hare and lynx. 1850 1875 1900 1925 Year 41

Figure 53.18 50 40 30 20 10 2,500 2,000 1,500 1,000 500 Wolves Moose Number of wolves Number of moose Figure 53.18 Fluctuations in moose and wolf populations on Isle Royale, 1959–2008. 1955 1965 1975 1985 1995 2005 Year 42

The Global Human Population Figure 53.22 The Global Human Population 7 6 5 4 3 2 1 The human population increased relatively slowly until about 1650 and then began to grow exponentially Human population (billions) The Plague Figure 53.22 Human population growth (data as of 2009). 8000 BCE 4000 BCE 3000 BCE 2000 BCE 1000 BCE 1000 CE 2000 CE 43

The global population is more than 6.8 billion people Though the global population is still growing, the rate of growth began to slow during the 1960s © 2011 Pearson Education, Inc.

Annual percent increase Figure 53.23 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 2009 Annual percent increase Projected data Figure 53.23 Annual percent increase in the global human population (data as of 2009). 1950 1975 2000 2025 2050 Year 45

Regional Patterns of Population Change To maintain population stability, a regional human population can exist in one of two configurations Zero population growth = High birth rate – High death rate Zero population growth = Low birth rate – Low death rate The demographic transition is the move from the first state to the second state © 2011 Pearson Education, Inc.

Rapid growth Afghanistan Slow growth United States No growth Italy Figure 53.24 Rapid growth Afghanistan Slow growth United States No growth Italy Male Female Age 85+ 80–84 75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0–4 Male Female Age 85+ 80–84 75–79 70–74 65–69 60–64 55–59 50–54 45–49 40–44 35–39 30–34 25–29 20–24 15–19 10–14 5–9 0–4 Male Female Figure 53.24 Age-structure pyramids for the human population of three countries (data as of 2009). 10 8 6 4 2 2 4 6 8 10 8 6 4 2 2 4 6 8 8 6 4 2 2 4 6 8 Percent of population Percent of population Percent of population 47

Age structure diagrams can predict a population’s growth trends The demographic transition is associated with an increase in the quality of health care and improved access to education, especially for women Most of the current global population growth is concentrated in developing countries Age structure diagrams can predict a population’s growth trends They can illuminate social conditions and help us plan for the future © 2011 Pearson Education, Inc.

Infant Mortality and Life Expectancy Infant mortality and life expectancy at birth vary greatly among developed and developing countries but do not capture the wide range of the human condition © 2011 Pearson Education, Inc.

Infant mortality (deaths per 1,000 births) Figure 53.25 60 50 40 30 20 10 80 60 40 20 Infant mortality (deaths per 1,000 births) Life expectancy (years) Figure 53.25 Infant mortality and life expectancy at birth in industrialized and less industrialized countries (data as of 2008). Indus- trialized countries Less indus- trialized countries Indus- trialized countries Less indus- trialized countries 50

Global Carrying Capacity How many humans can the biosphere support? Population ecologists predict a global population of 7.810.8 billion people in 2050 The carrying capacity of Earth for humans is uncertain The average estimate is 10–15 billion © 2011 Pearson Education, Inc.

Limits on Human Population Size The ecological footprint concept summarizes the aggregate land and water area needed to sustain the people of a nation It is one measure of how close we are to the carrying capacity of Earth Countries vary greatly in footprint size and available ecological capacity © 2011 Pearson Education, Inc.

Figure 53.26 Annual per capita energy use around the world. Gigajoules > 300 150–300 50–150 10–50 < 10 Figure 53.26 Annual per capita energy use around the world. 53

Population Ecology Chapter 35 Review Q’s Questions prepared by Eric Ribbens Western Illinois University John Zarnetske Hoosick Falls Central Schools

Which of the following sets of measurements is the most useful when studying populations? gene frequency over time and the ratio of reproductive to nonreproductive individuals density, dispersion, and demographics of a population minimum and minimum amounts of precipitation and annual temperature extremes ratio of predators and the number of immigrants and emigrants annual precipitation averages and mean annual temperatures Answer: b

Population ecologists are primarily interested in understanding how biotic and abiotic factors influence the density, distribution, size, and age structure of populations. the overall vitality of a population of organisms. how humans affect the size of wild populations of organisms. studying interactions among populations of organisms that inhabit the same area. how populations evolve as natural selection acts on heritable variations among individuals and changes in gene frequency. Answer: a

A mark-recapture study would be a good way to find out how many queens live in a beehive. cubs that black bears in Minnesota are likely to have. pine trees live in a forest. fish live in a lake. people speed on an interstate. Answer: d

from Type I to Type II or III. from Type II to Type I. Imagine that a species of fish used to be a broadcast spawner (producing many eggs that then get no subsequent parental care) but has evolved to be a mouth brooder (holding the eggs in the parent’s mouth until they hatch and then caring for the young for a while). We would expect the survivorship curve of this species to shift from Type I to Type II or III. from Type II to Type I. from Type III to Type I or II. from Type II to Type III. The survivorship type would vary unpredictably. Answer: c © 2011 Pearson Education, Inc.

The exponential growth model describes the increase in population size of a population that is not constrained by resources or space. The graph shows the elephant population in Kruger National Park, which appears to have been reproducing exponentially from 1900 to 1963. From this graph, you can tell that none of the elephants died. a female elephant living around 1960 was more likely to have a baby than a female elephant living around 1920. the elephants adapted to the new park conditions around 1955. the vegetation the elephants eat could support more than 5,000 elephants. the more elephants there are, the more tourists will visit the park. Answer: d

a) Paramecium are a single-celled organism. b) Daphnia live in water. The logistic model incorporates the idea of K, the carrying capacity, which is the maximum number of individuals the ecosystem can sustain over time. Essential to this idea is the concept that population growth rates are reduced when the population size approaches K. Look at the graphs on the next slide. Both Paramecium and Daphnia have population dynamics that stabilize around K. However, Daphnia overshot their carrying capacity, but Paramecium did not. This is probably because a) Paramecium are a single-celled organism. b) Daphnia live in water. c) the Daphnia had to learn what their carrying capacity was. d) the Paramecium population had a bigger K (about 800) than Daphnia (about 120). e) something about Daphnia responds differently to K than Paramecium. Answer: e

From the following graph you can tell that families in Mexico are still more likely to be bigger than families in Sweden. more people live in Mexico than in Sweden. birth rates and death rates do not appear to be correlated. a Swedish person born in 1900 is more likely to be dead than a Mexican person born in 1900. these populations are probably far away from their carrying capacity. Answer: a

The graph shows the percent increase in the global human population The graph shows the percent increase in the global human population. There is a sharp dip around 1960, which the legend says is due mainly to a famine in China in which 60 million people died. The graph also predicts that the percent increase is dropping and will continue to drop throughout the 21st century. Which of the following statements is true? The famine in China and the 21st-century decline are both examples of density-independent factors. The famine in China and the 21st-century decline are both examples of density-dependent factors. The famine in China was density-independent, but the 21st-century decline is density dependent. The famine in China was density-dependent, but the 21st-century decline is density independent. Because the causes of the famine and the 21st-century decline are different, you cannot tell whether they are density dependent. Answer: b

Most ecologists agree that people should not be using more than 1 Most ecologists agree that people should not be using more than 1.7 ha of resources if they want to be sustainable. People in the United States use an average of 10 ha. This implies that the ecological footprint concept is flawed. the United States has more land than other countries do. U.S. rates of resource consumption are too high. U.S. people are happier. U.S. people are less likely to emigrate. Answer: c