1. Population Ecology Chapter 45

2. Population A group of individuals of the same species occupying a given area Can be described by demographics  Vital statistics such as size density distribution age structure

3. Human Population Growth Population now exceeds 6 billion Rates of increase vary among countries Average annual increase is 1.26 percent Population continues to increase exponentially

4. Limits to Growth A population’s growth depends on the resources of its environment  Food  Space  Mates

5. Distribution patterns Density & Distribution

6. Determining Population Size Direct counts are most accurate but seldom feasible Can sample an area, then extrapolate Capture-recapture method is used for mobile species

7. Capture-Recapture Method Capture, mark, and release individuals Return later and capture second sample Count the number of marked individuals and use this to estimate total population Assumptions  Marking has no effect on mortality  Marking has no effect on likelihood to being captured  no immigration or emigration between sampling times

8. Changes in Population Size Immigration adds individuals Emigration subtracts individuals Births add individuals Deaths subtract individuals Human population growth Human Population II

9. Zero Population Growth Interval in which number of births is balanced by number of deaths Assume no change as a result of migration Population size remains stable

10. r Net reproduction per individual per unit time Variable combines per capita birth and death rates (assuming both constant) Can be used to calculate rate of growth of a population

11. Exponential Growth Equation G = rN G is population growth per unit time r is net reproduction per individual per unit time N is population size

12. Exponential growth Exponential Growth

13. Population size expands by ever increasing increments during successive intervals The larger the population gets, the more individuals there are to reproduce

14. Effect of Deaths Population grows exponentially as long as per capita death rates are lower than per capita birth rates 25% mortality between divisions

15. Biotic Potential Maximum rate of increase per individual under ideal conditions Varies between species In nature, biotic potential is rarely reached

16. Limiting Factors Any essential resource that is in short supply All limiting factors acting on a population dictate sustainable population size

17. Carrying Capacity (K) Maximum number of individuals that can be sustained in a particular habitat Logistic growth occurs when population size is limited by carrying capacity

18. Logistic Growth Equation G = r max N (K-N/K) G = population growth per unit time r max = maximum population growth rate per unit time N = number of individuals K = carrying capacity

19. Logistic Growth As size of the population increases, rate of reproduction decreases When the population reaches carrying capacity, population growth ceases

20. initial carrying capacity new carrying capacity Logistic Growth Graph

21. Effect of death on growth Logistic Growth

23. Overshooting Capacity Population may temporarily increase above carrying capacity Overshoot is usually followed by a crash; dramatic increase in deaths Reindeer on St. Matthew’s Island

24. Density-Dependent Controls Logistic growth equation deals with density- dependent controls Limiting factors become more intense as population size increases  Disease / parasites  Competition  Predator / prey  Toxic effects of waste products  Crowding / stress

25. Density-Independent Controls Factors unaffected by population density Natural disasters or climate changes affect large and small populations alike  Hurricanes  Tornados  Droughts  Floods  Earthquakes  Volcanoes

26. Life history patterns Survivorship

30. Human Population Problems Over 6 billion people alive About 2 billion live in poverty Most resources are consumed by the relatively few people in developed countries

31. Side-Stepping Controls Expanded into new habitats Agriculture increased carrying capacity; use of fossil fuels aided increase Hygiene and medicine lessened effects of density-dependent controls

32. domestication of plants, animals 9000 B.C. (about 11,000 years ago) agriculturally based urban societies beginning of industrial, scientific revolutions Estimated size by 10,000 years ago 5 million By 1804 1 billion By 1927 2 billion By 1960 3 billion By 1974 4 billion By 1987 5 billion By 1999 6 billion Projected for 2050 8.9 billion

33. Future Growth Exponential growth cannot continue forever Breakthroughs in technology may further increase carrying capacity Eventually, density-dependent factors will slow growth

34. Fig. 45-20, p.817

35. Fertility Rates Worldwide, average annual rate of increase is 1.26% Total fertility rate (TFR) is average number of children born to a woman Highest in developing countries, lowest in developed countries

36. Population Age Structure Divide population into age categories Population’s reproductive base includes members of the reproductive and pre- reproductive age categories

37. Age structure diagrams Age Structure Diagrams

38. Population Momentum Lowering fertility rates cannot immediately slow population growth rate Why?  There are already many future parents alive If every couple had just two children, population would still keep growing for another 60 years

39. U.S. age structure Population Momentum

40. Slowing Growth in China World’s most extensive family planning program Government rewards small family size, penalizes larger families, provides free birth control, abortion, sterilization Since 1972, TFR down to 1.8 from 5.7

41. Effects of Economic Development Total fertility rates (TFRs) are highest in developing countries, lowest in developed countries When individuals are economically secure, they are under less pressure to have large families

43. Current and projected population sizes by region Effects of Economic Development

44. Demographic Transition Model Stage 1 Preindustrial Stage 2 Transitional Stage 3 Industrial Stage 4 Postindustrial births deaths relative population size lowincreasingvery highdecreasinglowzeronegative Fig. 45.19 p. 816

45. Demographic transition model Demographic Transition Model

46. Resource Consumption United States has 4.7 percent of the world’s population Americans have a disproportionately large effect on the world’s resources Per capita, Americans consume more resources and create more pollution than citizens of less developed nations