Population Ecology

1. Population Ecology

2. Population Ecology Certain ecological principles govern the growth and sustainability of all populations--including human populations

3. Ecological Principles Apply to All Species Humans, Palms, Crabs, Seagulls, algae, etc.

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

5. Angel Island

6. Angel Island 1 • A. Angel Island is a game reserve in San Francisco Bay near Sausalito  • B. In the early 1900's well-meaning nature lovers introduced deer to the island • C. With no natural predators to control them the population quickly rose to a level much higher than the island could support • D. Well meaning people brought food to the island to feed the deer, causing the population to further increase

7. Angel Island 2 • E. Eventually the population grew to over 300, much too large for the island to support • F. As the deer began to starve they ate most of the native vegetation. Without vegetation the soil started washing away and the island environment rapidly deteriorated

8. Angel Island - 3 • G. It was proposed that hunters kill some of the deer and/or that coyotes, the deer’s natural predators, be introduced to the island. However many people objected because they viewed both alternatives as cruel • H. Eventually two thirds of the population was rounded up and moved to the mainland, at a cost of $3,000 per deer

9. Angel Island - 4 • I. However, tracking studies revealed that the majority of the deer moved to the mainland were killed by cars, dogs, coyotes and hunters within 60 days • J. The story of Angel Island illustrates a basic ecological principle: a population's growth is dependent on the resources of its environment. Human intervention could only postpone, not prevent the inevitable

10. Angel Island - 5 • K. Many environmental problems are simply the result of a lack of understanding of basic ecological principles by politicians, lawyers, economists, the general public and even well intentioned "environmentalists". Human ignorance of simple ecological principles often leads to disastrous results • From: http://arnica.csustan.edu/boty1050/Ecology/ecology.htm

11. 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

12. Population Growth • For most of human history, humans have not been very numerous compared to other species. • It took all of human history to reach 1 billion. • 150 years to reach 3 billion. • 12 years to go from 5 to 6 billion. • Human population tripled during the twentieth century.

13. Human Population History

14. U.S. POPClock Projection • According to the U.S. Bureau of the Census, the resident population of the United States, projected to 03/21/05 at 17:04 GMT (EST+5) is • 295,707,750 • COMPONENT SETTINGS • One birth every.................................. 7 seconds One death every.................................. 11 seconds One international migrant (net) every............ 24 seconds Net gain of one person every..................... 12 seconds

15. Population • A group of individuals of the same species occupying a given area during a particular period of time • Can be described by demographics • Vital statistics such as size, density, distribution, and age structure

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

17. Population Age Structure Diagram

18. 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 Figure 45.2 Page 808  random

19. Clumped Distribution

20. 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

21. Population Estimate • How could you determine the population size of the students in Robinson Hall? The number of revelers on the beach?

22. Does Time and Place Make a Difference? Hilton Head Daytona Beach

23. 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

24. Example:Capture - Recapture • In 1970, naturalists wanted to estimate the number of pickerel fish in Dryden Lake in central New York State. They captured 232 pickerel, put a mark on their fins, and returned the fish to the lake. Several weeks later, another sample of 329 pickerel fish were captured. Of this second sample, 16 had marks on their fins. (Chaterjee in Mosteller et al. Statistics by Example: Finding Models).

25. Chain Pickerel

26. How Many Pickerel Were in the Lake? • N = total number of pickerel in lake • NM = total number of marked pickerel (232) • RC = Number of recaptured pickerel (16) • NS = number of fish in sample (329) • NM/N = RC/NS • N = (NM x NS)/RC

27. Solution • N = (232 x 329)/16 • N = 4770 pickerel in the lake (estimate) • This is an example of how the “Capture/Recapture” method works.

28. Assumptions • The sampling is random • The marked organisms will not be harmed by the capture and markings • The marked organisms will not avoid recapture • The samples are statistically large enough to avoid problems with sampling error • No significant emigration/immigration occurs • The sampling is done promptly

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

30. 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

31. 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

32. r • Net reproduction per individual per unit time (Intrinsic rate of natural increase) a constant the units are inverse time • Variable combines per capita birth and death rates (assuming both constant) • Can be used to calculate rate of growth of a population

33. 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

34. Exponential Growth • Population size expands by ever increasing increments during successive intervals • The larger the population gets, the more individuals there are to reproduce Figure 45.4 Page 810

35. (r) Strategies • Short life • Rapid growth • Early maturity • Many small offspring. • Little parental care. • Little investment in individual offspring. • Adapted to unstable environment. • Pioneers, colonizers • Niche generalists • Prey • Regulated mainly by extrinsic factors. • Low trophic level.

36. Weedy Species – “r Strategists” • Opportunistic Species - Quickly appear when opportunities arise. • Many weeds. • Pioneer Species - Can quickly colonize open, disturbed, or bare ground.

37. Effect of Deaths • Population grows exponentially as long as per capita death rates are lower than per capita birth rates 25% mortality between divisions Figure 45.5 Page 811

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

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

40. 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

41. Logistic Growth Equation G = rmaxN ((K-N)/K) • G = population growth per unit time • rmax = maximum population growth rate per unit time • N = number of individuals • K = carrying capacity

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

43. Logistic Growth Graph initial carrying capacity new carrying capacity Figure 45.6 Page 812

44. K Strategists • Long life • Slower growth • Late maturity • Fewer large offspring. • High parental care and protection. • High investment in individual offspring.

45. More on K Strategists • Adapted to stable environment. • Later stages of succession. • Niche specialists • Predators (often, but not always) • Regulated mainly by intrinsic factors. • High trophic level.

46. Top Predators

47. 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 Figure 45.6 Page 812

48. 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

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

50. A Hurricane is an Example of a Density Independent Factor