Population Ecology

1. Population Ecology

2. 54 Population Ecology • 54.1 How Do Ecologists Study Populations? • 54.2 How Do Ecological Conditions Affect Life Histories? • 54.3 What Factors Influence Population Densities? • 54.4 How Do Spatially Variable Environments Influence Population Dynamics? • 54.5 HowCan We Manage Populations?

3. What’s a population? all the individuals of a species in a given area. Population structure describes the age distribution of individuals, and how those individuals are spread over the environment.

4. Photo 54.1 Rookery of northern elephant seals (Mirounga angustirostrus), Baja California.

5. Population Density? The number of individuals per unit area or volume is the population density. Density has strong influence over how individuals react with one another and with populations of other species.

6. demographic events: births, deaths, immigration, and emigration Change the pop density demography

7. Factors population ecologists study: # and density of individuals Tagging, marking rates of demographic events locations of individuals Tracking physiological & environmental data

8. Figure 54.1 By Their Marks You May Know Them

11. Figure 54.2 Hydrogen Isotopes Tell Where Migratory American Redstarts Molted Their Feathers What are molecular marker examples? Useful? H isotopes -- where American redstarts molt during migrations Isotopes in feathers reflect the latitude at which the feathers grew strong latitudinal gradient of these isotopes in precipitation

12. Population Estimates & Statistics to Extrapolate Mobile animals: capture, mark, recapture method Proportion of marked individuals in the new sample is used to estimate population size:

13. Accurate? ONLY if marked individuals randomly mix with the unmarked ones, and both are equally likely to be captured Some animals learn to avoid traps, or learn that traps provide food and become “trap-happy.”

14. Equation for estimating N (pop size)

15. Table 54.1 Life Table of the 1978 Cohort of the Cactus Finch on Isla Daphne (Part 1)

16. LIFE TABLE life table:track a group of individuals born @ same time (cohort) Survivorship: # still alive at later dates fecundity: # offspring produced in a time interval

17. Table 54.1 Life Table of the 1978 Cohort of the Cactus Finch on Isla Daphne (Part 2)

18. Life tables can be used to predict future trends. For cactus finch, mortality rate was high during the first year, then dropped. Mortality rate fluctuated year to year because the birds are dependent on seed production, which fluctuates with rainfall.

19. Figure 54.3 Survivorship Curves: survivorship in relation to age---3 MAIN PATTERNS!

20. Figure 54.4 Age Distributions (Age Structure Diagrams) Change over Time average family size increased from 2.5 to 3.8 children

21. 54.2 Life Histories

22. What’s a life history? describes how it allocates time and energy among the various activities throughout its life can vary dramatically single offspring per reproductive episode....or lots! Some reproduce only once and then die (salmon, agave)

23. Figure 54.5 Big Bang Reproduction

24. Figure 54.6 An Oil Droplet Is an Energy Kick Start Why are wildlife biologists interested?

25. *Fishery Management* Black rockfish females continue to grow throughout their lives large females produce many more eggs than small ones Eggs from older females contain oil droplets that are food for developing fish, so offspring have abetter chance for survival.

26. Cont.-- Intensive fishing off Oregon from 1996–1999 reduced average age of females from 9.5 to 6.5 years. Age reduction decreased number of eggs produced and average growth rates of offspring. Maintaining populations of this species may require no-fishing zones where females can grow to large sizes.

27. Local Red Drum Research http://www.dnr.sc.gov/marine/mrri/insh_fish/reddrum/reddrumportal1.html

28. Guppies in Trinidad? Influence of predation If predator fish are excluded (by waterfalls)  fish have much lower mortality rates When reared in the lab, guppies from the high predation site matured earlier, produced more eggs, and produced more offspring per brood.

29. 54.3 Population Densities

30. Photo 54.4 Dogwinkles and barnacles in the intertidal zone.

31. Photo 54.5 Dense colony of purple sea urchins (Strongylocentrotus purpuratus).

32. Photo 54.6 Winter swarm of ladybugs (Hippodanina convergens).

33. dn dt equation... ΔN/Δt = rate of change of pop over time r = net reproductive rate

34. rmax = intrinsic rate of increase

35. Is this intrinsic rate possible in nature? YES! Over short time periods, close to rmax northern elephant seals were hunted to near extinction: populations grew exponentially on some islands after hunting was stopped

36. Figure 54.7 Exponential Population Growth

37. But then the population reaches the .... The environmental carrying capacity (K) # of any particular species that can be supported in an environment Environmental limits  birth rates decrease, death rates increase

38. What determines K? availability of resources Food, shelter Diseases and parasites Social interactions S-shaped curve = logistic growth

39. Figure 54.8 Logistic Population Growth

40. Logistic growth model Growth stops when N = K

41. Density-dependent factors: pop density increases food supplies may be depleted Predators may be attracted to high densities of prey, increasing death rate. Diseases can spread more easily.

42. Density-Independent Factors: Weather-related phenomena

43. Figure 54.9 Regulation of an Island Population of Song Sparrows (Part 1)

44. Figure 54.9 Regulation of an Island Population of Song Sparrows (Part 2)

45. Figure 54.9 Regulation of an Island Population of Song Sparrows (Part 3)

46. Song sparrows on Mandarte Island 12 yr study Population size fluctuated significantly. Death rates high during cold, snowy winters, regardless of population density.

47. Density-dependent factors were also important: # breeding males limited by territorial behavior more breeding females  fewer offspring each one fledged more birds alive in autumn  less chance juveniles would survive the winter

48. Photo 54.7 Thorny tree swarms with locusts, Burkina Faso.

49. Photo 54.8 Adult Chinook salmon is released into holding tank at a hatchery in British Columbia.

50. General Trend: More stable population # in species with long-lived individuals and low reproductive rates. Insect pops fluctuate more than birds and mammals. Environmental factors can change carrying capacity for species.