1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 53 Population Ecology http://video.nationalgeographic.com/video/news/ 7-billion/ngm-7billion

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Earths Fluctuating Populations To understand human population growth – We must consider the general principles of population ecology Population ecology is the study of populations in relation to environment – Including environmental influences on: – population density and distribution – age structure – variations in population size

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The fur seal population of St. Paul Island, off the coast of Alaska – Is one that has experienced dramatic fluctuations in size Figure 52.1

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A population – Is a group of individuals of a single species living in the same general area 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

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Density is the result of a dynamic interplay – Between processes that add individuals to a population and those that remove individuals from it Belding’s ground squirrel Births and immigration add individuals to a population. BirthsImmigration PopuIation size Emigration Deaths Deaths and emigration remove individuals from a population.

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Environmental & social factors influence 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.

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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.

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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.

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Demography Demography is the study of the vital statistics of a population – And how they change over time – Death rates and birth rates 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

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The survivorship curve for Belding’s ground squirrels – Shows that the death rate is relatively constant – Three types of surviorship curves 1000 100 10 1 Number of survivors (log scale) 0 2 46 810 Age (years) Males Females I II III 50 100 0 1 10 100 1,000 Percentage of maximum life span Number of survivors (log scale)

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Life history traits are products of natural selection Life history traits affect an organisms reproductive and survival schedule. – Reflected in the development, physiology, and behavior of an organism Species that exhibit semelparity, or “big-bang” reproduction – Reproduce a single time and die

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Species that exhibit iteroparity, or repeated reproduction – Produce offspring repeatedly over time – Some lizards produce a few large eggs What factors contribute to the evolution of semelparity or iteroparity?

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings “Trade-offs” and Life Histories Trade-offs between survival and reproduction Researchers in the Netherlands studied the effects of parental caregiving in European kestrels over 5 years. The researchers transferred chicks among nests to produce reduced broods (three or four chicks), normal broods (five or six), and enlarged broods (seven or eight). They then measured the percentage of male and female parent birds that survived the following winter. (Both males and females provide care for chicks.) EXPERIMENT The lower survival rates of kestrels with larger broods indicate that caring for more offspring negatively affects survival of the parents. CONCLUSION 100 80 60 40 20 0 Reduced brood size Normal brood size Enlarged brood size Parents surviving the following winter (%) Male Female RESULTS

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Selective pressures influence trade-offs 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.

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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.

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The exponential model of population growth The exponential model describes population growth in an idealized, unlimited environment – to understand the capacity of species for increase and the conditions that may facilitate this type of growth

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Zero population growth – Occurs when the birth rate equals the death rate The population growth equation can be expressed as dN dt  rN

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exponential Growth 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 dN dt  r max N

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exponential population growth – Results in a J-shaped curve Figure 52.9 0 5 1015 0 500 1,000 1,500 2,000 Number of generations Population size (N) dN dt  1.0N dN dt  0.5N

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The J-shaped curve of exponential growth – Is characteristic of some populations that are rebounding Figure 52.10 1900 1920194019601980 Year 0 2,000 4,000 6,000 8,000 Elephant population

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Logistic growth model and 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

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Logistic Growth Model In the logistic population growth model – The per capita rate of increase declines as carrying capacity is reached, as N increases Figure 52.11 Maximum Positive Negative 0 N  KN  K Population size (N) Per capita rate of increase (r)

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The logistic growth equation – Includes K, the carrying capacity – Fits few real populations, good for estimating population growth dN dt  ( K  N ) K r max N

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A hypothetical example of logistic growth Table 52.3

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The logistic model of population growth – Produces a sigmoid (S-shaped) curve Figure 52.12 dN dt  1.0N Exponential growth Logistic growth dN dt  1.0N 1,500  N 1,500 K  1,500 0 51015 0 500 1,000 1,500 2,000 Number of generations Population size (N)

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 52.13a 800 600 400 200 0 Time (days) 05 10 15 (a) A Paramecium population in the lab. The growth of Paramecium aurelia in small cultures (black dots) closely approximates logistic growth (red curve) if the experimenter maintains a constant environment. 1,000 Number of Paramecium/ml The Logistic Model and Real Populations The growth of laboratory populations of paramecia – Fits an S-shaped curve

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some populations overshoot K Some populations fluctuate 180 150 0 120 90 60 30 Time (days) 0 160 140120 80 1006040 20 Number of Daphnia/50 ml (b) A Daphnia population in the lab. The growth of a population of Daphnia in a small laboratory culture (black dots) does not correspond well to the logistic model (red curve). This population overshoots the carrying capacity of its artificial environment and then settles down to an approximately stable population size. 0 80 60 40 20 1975 19801985 1990 19952000 Time (years) Number of females (c) A song sparrow population in its natural habitat. The population of female song sparrows nesting on Mandarte Island, British Columbia, is periodically reduced by severe winter weather, and population growth is not well described by the logistic model.

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Logistic Model and Life Histories K-selection, or density-dependent selection – Selects for life history traits that are sensitive to population density – Competitive behaviors r-selection, or density-independent selection – Selects for life history traits that maximize reproduction in uncrowded environments – Overproduction

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Populations are regulated by biotic and abiotic influences What environmental factors stop a population from growing? Why do some populations show radical fluctuations in size over time, while others remain stable?

30. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population Change and Population Density 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 Density-dependent birth rate Density- dependent death rate Equilibrium density Density-dependent birth rate Density- independent death rate Equilibrium density Density- independent birth rate Density-dependent death rate Equilibrium density 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.

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In crowded populations, increasing population density – Intensifies intraspecific competition for resources Figure 52.15a,b 100100 0 1,000 10,000 Average number of seeds per reproducing individual (log scale) Average clutch size Seeds planted per m 2 Density of females 0 7010 2030 40506080 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. Density Dependent Regulation

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Territoriality Health/pathogens Predation Toxic waste buildup Intrinsic, physiological, factors (aggression, stress syndrome) Density Dependent Regulation

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stability and Fluctuation – Populations of large mammals are not as stable as we thought – Extreme fluctuations often found in invertebrates 1960 197019801990 2000 Year Moose population size 0 500 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 1950 19601970 1980 Year 1990 10,000 100,000 730,000 Commercial catch (kg) of male crabs (log scale)

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings High levels of immigration combined with higher survival – Can result in greater stability in populations Figure 52.20 Mandarte island Small islands Number of breeding females 198819891990 1991 Year 0 10 20 30 40 50 60 Metapopulations and Immigration

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population Cycles Many populations – Undergo regular boom-and-bust cycles Figure 52.21 Year 1850187519001925 0 40 80 120 160 0 3 6 9 Lynx population size (thousands) Hare population size (thousands) Lynx Snowshoe hare

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Global Human Population The human population – Increased relatively slowly until about 1650 and then began to grow exponentially Figure 52.22 8000 B.C. 4000 B.C. 3000 B.C. 2000 B.C. 1000 B.C. 1000 A.D. 0 The Plague Human population (billions) 2000 A.D. 0 1 2 3 4 5 6

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Though the global population is still growing – The rate of growth began to slow approximately 40 years ago Figure 52.23 1950 19752000 2025 2050 Year 2003 Percent increase 2.2 2 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 1.8

38. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Age Structure – The relative number of individuals at each age Rapid growth Afghanistan Slow growth United States Decrease Italy Male Female Male FemaleMale Female Age 864202468864202468864202468 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 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

39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Developed countries Developing countries Infant mortality (deaths per 1,000 births) Life expectancy (years) 60 50 40 30 20 10 0 80 60 40 20 0

40. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecological footprints for 13 countries – Show that the countries vary greatly in their footprint size and their available ecological capacity Figure 52.27 16 14 12 10 8 6 4 2 0 0 2 4 68 1214 16 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)