1. Population Ecology Chapter 27

2. Population Ecology Certain ecological principles govern the growth and sustainability of all populations Human populations are no exception

3. Limits to Growth A population’s growth depends on the resources of its environment Deer introduced to Angel Island –Population outstripped resources

4. 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

5. 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, and age structure

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

7. Density & Distribution Number of individuals in some specified area of habitat Crude density information is more useful if combined with distribution data clumped nearly uniform random

8. 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

9. 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

10. Assumptions in Capture-Recapture Marking has no effect on mortality Marking has no effect on likelihood to being captured There is no immigration or emigration between sampling times

11. Changes in Population Size Immigration adds individuals Emigration subtracts individuals Births add individuals Deaths subtract individuals

12. population growth per unit time net population growth rate per individual per unit time number of individuals =X in-text, p. 688

13. 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

14. Per Capita Rates Rates per individual Total number of events in a time interval divided by the number of individuals Per capita birth rate per month = Number of births per month Population size

15. 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

16. 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

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

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

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

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

21. 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

22. 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

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

24. animation Click to view animation.

25. Overshooting Capacity Population may temporarily increase above carrying capacity Overshoot is usually followed by a crash; dramatic increase in deaths

26. Density-Dependent Controls Logistic growth equation deals with density-dependent controls Limiting factors become more intense as population size increases Disease, competition, parasites, toxic effects of waste products

27. Density-Independent Controls Factors unaffected by population density Natural disasters or climate changes affect large and small populations alike

28. Fig. 40.6, p. 690 initial carrying capacity new carrying capacity