1. Chapter 52 Population Ecology

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population ecology Study of populations in relation to environment – Including environmental influences on Population density, distribution, demography Population growth models Regulation of populations Human population growth

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Density and Dispersion Density - number of individuals within a boundary Figure 52.2 Births and immigration add individuals to a population. BirthsImmigration PopuIation size Emigration Deaths Deaths and emigration remove individuals from a population. Changed by: - births and deaths -immigration and emigration

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dispersion Pattern of spacing among individuals Influenced by environmental and social factors Figure 52.17

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Clumped dispersion Based on 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.

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Uniform dispersion Social interactions, eg. territoriality, competition 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.

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Random dispersion Usually homogeneous habitat – No attractions or repulsions between individuals Figure 52.3c (c) Random. Dandelions grow from windblown seeds that land at random and later germinate.

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Demography Describing a population by vital statistics: - birth rate - death rate - sex ratio - age structure

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Demography Life table: age specific summary of survival patterns of a population

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Survivorship Curves Graphic way of representing life table – Belding’s ground squirrels - death rate ~constant Figure 52.4 1000 100 10 1 Number of survivors (log scale) 0 2 46 810 Age (years) Males Females

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Survivorship Curves Three general types: – Type I, Type II, and Type III Figure 52.5 I II III 50 100 0 1 10 100 1,000 Percentage of maximum life span Number of survivors (log scale)

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Minutes Months 1 year 4-5 years 5 years 5-11 years many years Reproduction

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Does human reproductive table follow this pattern? Reproductive table

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings SEMELPARITY = breed only once (“big bang”)

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ITEROPARITY = breed more than once - frequency depends on: environment – food, etc. inherent biology eg. elephants – 22 month gestation - long maternal care period

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Why not do both? Organisms have finite resources Figure 52.7 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

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fecundity = number of offspring per reproductive episode Varies with species and environment elephants and whales 1 squirrels2-6 oak treesthousands of acorns salmonthousands of eggs many invertebrateshundreds of thousands of eggs

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plant parenting Many small seeds or fewer large seeds (a) Most weedy plants, such as this dandelion, grow quickly and produce a large number of seeds. (b) Some plants, such as this coconut palm, produce a moderate number of very large seeds.

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population growth models exponential growth requires an idealized environment E. Coli growth curve

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exponential population growth J-shaped curve Resource limitations not a factor 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

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings J-shaped curve 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

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings “ I think I may fairly make two postulata. First, that food is necessary to the existence of man. Secondly, that the passion between the sexes is necessary and will remain nearly in its present state... Population, when unchecked, increases in a geometrical ratio: Subsistence increases only in an arithmetical ratio. A slight acquaintance with numbers will show the immensity of the first power in comparison of the second.” Thomas Malthus, 1798

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population Food Time Abundance or Density Malthus (1798) was the first to recognize the potential for populations to grow beyond the resources that can support them.

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Potential population growth Resources Time Abundance or Density Actual population growth Does it really happen?

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Potential population growth Resources Time Abundance or Density Darwin (Campbell, p. 435) 1.Species have potential to increase population size exponentially 2.Most do not; resources are limited. 3.More individuals are produced than the environment can support. 4.This leads to a struggle for existence, with only a fraction of offspring surviving each generation. 5.Individuals vary, variation is heritable, and survival and reproduction depend on hereditary constitution 6.Unequal ability to survive and reproduce leads to change in a population Actual population growth Population and evolutionary change

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings U.S. 295,995,954 World 6,438,377,202 14:44 GMT (EST+5) Apr 29, 2005 What about humans?

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Logistic growth model Includes concept of carrying capacity (K) – maximum population size the environment can support Exponential growth cannot be sustained This model limits growth by incorporating carrying capacity

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Logistic model 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)

30. 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 Real Populations Laboratory populations of paramecia – S-shaped curve

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Real populations Some overshoot K then stabilize Figure 52.13b 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.

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some populations – Fluctuate greatly around K. Why? Figure 52.13c 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.

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Life history traits K-selection, or density-dependent selection – Selects for traits sensitive to population density r-selection, or density-independent selection – Selects for traits that maximize reproduction

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Populations regulated by: complex interaction of biotic and abiotic influences So – – What environmental factors stop a population from growing? – Why do some populations show radical fluctuations in size over time

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population Change 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

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population Regulation Density-dependent birth and death rates – Are an example of negative feedback that regulates population growth – Are affected by many different mechanisms

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Competition for Resources Increasing population density – Intensifies intraspecific competition 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.

38. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Territoriality Cheetahs mark boundaries Figure 52.16

39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population density Also influenced by – Disease – Predation – Toxic wastes – Intrinsic factors eg. stress

40. 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

41. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Meadow Vole (Field Mouse)

42. Studies on Voles in Mission Valley, Western Montana (1999-2003)

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

44. N = 77 N = 44

45. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings N = 533 N = 44

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

48. Number of voles per site in 2001 (year of peak abundance) Biological organisms are not evenly distributed in nature: Abundance varies in Time AND Space

49. What are interesting questions?

50. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings What causes changes in numbers of biological organisms over time and space? What are the mechanisms of change? What are the biological consequences of changes in numbers (so what?)? Why do patterns and mechanisms differ among species and areas?

51. Nutrients in rodent biomass, reduced plant growth, or impacts of grazing on plants Predator response (individual and population)

52. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vole predators in western Montana grasslands Grizzly bears Coyotes Foxes Weasels Hawks (various) Owls (various) Skunks Ravens Gulls Snakes (various) Love to eat them mousies, mousies what I love to eat. Bite they little heads off, nibble on they tiny feet

53. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A Predator’s View of Vole Populations

54. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Vole predators in western Montana grasslands Grizzly bears Coyotes Foxes Weasels Hawks (various) Owls (various) Skunks* Ravens* Gulls* Snakes* (various) *Significant nest predators when other prey unavailable

55. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Prey (voles) abundant Nest predation low Bird reproductive success high Predator populations grow Predator populations remain high Nest predation high Bird reproductive success low

56. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Human population growth - has slowed after centuries of exponential increase No population can grow indefinitely – And humans are no exception

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

58. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Still growing but…. 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

59. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Age structure represented in pyramids Figure 52.25 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

60. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecological Footprint 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

61. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Ecological footprints Countries vary greatly in footprint size and 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)