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LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 36 Population Ecology Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc. • 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. Figure 53.3 Births Births and immigration add individuals to a population. Immigration Deaths Deaths and emigration remove individuals from a population. Emigration Figure 53.4 (a) Clumped Patterns of Dispersion (b) Uniform (c) Random • Most organisms exhibit a clumped dispersion pattern (i.e. herds, packs, etc). © 2011 Pearson Education, Inc. Figure 53.4a (a) Clumped • 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 • 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 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 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. Figure 53.5 Number of survivors (log scale) 1,000 100 Females 10 Males 1 0 2 4 6 Age (years) 8 10 • 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 10 III 1 0 50 Percentage of maximum life span 100 Measuring Population Growth Rates Change in Immigrants Emigrants population Births entering Deaths leaving size population population • 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. Figure 53.7 2,000 Population size (N) dN = 1.0N dt 1,500 dN = 0.5N dt 1,000 500 0 5 10 Number of generations 15 Figure 53.8 Elephant population 8,000 6,000 4,000 2,000 0 1900 1910 1920 1930 1940 Year 1950 1960 1970 The elephant population in Kruger National Park, South Africa, grew exponentially after hunting was banned 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. Figure 53.9 Exponential growth dN = 1.0N dt Population size (N) 2,000 1,500 K = 1,500 Logistic growth 1,500 – N dN = 1.0N 1,500 dt ( 1,000 Population growth begins slowing here. 500 0 0 5 10 Number of generations 15 ) Number of Daphnia/50 mL Number of Paramecium/mL Figure 53.10 1,000 800 600 400 200 0 0 5 10 Time (days) 15 (a) A Paramecium population in the lab 180 150 120 90 60 30 0 0 20 40 60 80 100 120 140 160 Time (days) (b) A Daphnia population in the lab 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. 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 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-andbust cycle of hare populations © 2011 Pearson Education, Inc. Figure 53.19 Snowshoe hare 120 9 Lynx 80 6 40 3 0 0 1850 1875 1900 Year 1925 Number of lynx (thousands) Number of hares (thousands) 160 Figure 53.18 2,500 Wolves Moose 40 2,000 30 1,500 20 1,000 10 500 0 1955 0 1965 1975 1985 Year 1995 2005 Number of moose Number of wolves 50 Figure 53.22 The Global Human Population • The human population increased relatively slowly until about 1650 and then began to grow exponentially 6 5 4 3 2 The Plague 1 0 8000 BCE 4000 BCE 3000 BCE 2000 BCE 1000 BCE 0 1000 CE 2000 CE Human population (billions) 7 • 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. Figure 53.23 2.2 2.0 Annual percent increase 1.8 1.6 1.4 2009 1.2 Projected data 1.0 0.8 0.6 0.4 0.2 0 1950 1975 2000 Year 2025 2050 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. Figure 53.24 Rapid growth Afghanistan Male 10 8 Female 6 4 2 0 2 4 6 Percent of population Slow growth United States 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 8 10 8 Male Female 6 4 2 0 2 4 6 Percent of population No growth Italy 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 8 8 Male Female 6 4 2 0 2 4 6 8 Percent of population • 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. 80 60 50 Life expectancy (years) Infant mortality (deaths per 1,000 births) Figure 53.25 40 30 20 60 40 20 10 0 0 Indus- Less industrialized trialized countries countries Indus- Less industrialized trialized countries countries Global Carrying Capacity How many humans can the biosphere support? • Population ecologists predict a global population of 7.810.8 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 Gigajoules > 300 150–300 50–150 10–50 < 10 Figure 53.26 Annual per capita energy use around the world. LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 35 Review Q’s Population Ecology Questions prepared by Eric Ribbens Western Illinois University by JohnLectures Zarnetske Hoosick Falls Erin CentralBarley Schools Kathleen Fitzpatrick © 2011 Pearson Education, Inc. Which of the following sets of measurements is the most useful when studying populations? a) gene frequency over time and the ratio of reproductive to nonreproductive individuals b) density, dispersion, and demographics of a population c) minimum and minimum amounts of precipitation and annual temperature extremes d) ratio of predators and the number of immigrants and emigrants e) annual precipitation averages and mean annual temperatures Population ecologists are primarily interested in a) understanding how biotic and abiotic factors influence the density, distribution, size, and age structure of populations. b) the overall vitality of a population of organisms. c) how humans affect the size of wild populations of organisms. d) studying interactions among populations of organisms that inhabit the same area. e) how populations evolve as natural selection acts on heritable variations among individuals and changes in gene frequency. A mark-recapture study would be a good way to find out how many a) queens live in a beehive. b) cubs that black bears in Minnesota are likely to have. c) pine trees live in a forest. d) fish live in a lake. e) people speed on an interstate. 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 a) b) c) d) e) 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. © 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 a) none of the elephants died. b) a female elephant living around 1960 was more likely to have a baby than a female elephant living around 1920. c) the elephants adapted to the new park conditions around 1955. d) the vegetation the elephants eat could support more than 5,000 elephants. e) the more elephants there are, the more tourists will visit the park. 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. From the following graph you can tell that a) families in Mexico are still more likely to be bigger than families in Sweden. b) more people live in Mexico than in Sweden. c) birth rates and death rates do not appear to be correlated. d) a Swedish person born in 1900 is more likely to be dead than a Mexican person born in 1900. e) these populations are probably far away from their carrying capacity. 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? a) The famine in China and the 21st-century decline are both examples of density-independent factors. b) The famine in China and the 21st-century decline are both examples of density-dependent factors. c) The famine in China was density-independent, but the 21st-century decline is density dependent. d) The famine in China was density-dependent, but the 21st-century decline is density independent. e) Because the causes of the famine and the 21st-century decline are different, you cannot tell whether they are density dependent. 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 a) the ecological footprint concept is flawed. b) the United States has more land than other countries do. c) U.S. rates of resource consumption are too high. d) U.S. people are happier. e) U.S. people are less likely to emigrate.