Population Ecology and Ecosystems

1. Population Ecologyand Ecosystems Concepts and Applications: Chapters 40 & 43 Basic Concepts: Chapters 27 & 30 http://darwin.bio.uci.edu/~sustain/bio65/lec16/b65lec16.htm

2. PopulationEcology Ecology Ecology: The study of how organisms interact with one another and with their environment • Certain ecological principles govern the growth and sustainability of all populations • Human populations are no exception

3. PopulationEcology 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

4. PopulationEcology 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

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

6. PopulationEcology Density & Distribution • Number of individuals in some specified area of habitat • Crude density information is more useful if combined with distribution data Fig 40.2

7. PopulationEcology Mark and Recapture # marked Captured = Number released Total Captured Total Pop 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

8. PopulationEcology 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

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

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

11. PopulationEcology 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

12. PopulationEcology Exponential Growth Fig 40.4 • Population size expands by ever increasing increments during successive intervals • The larger the population gets, the more individuals there are to reproduce

13. PopulationEcology 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

14. PopulationEcology 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

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

16. PopulationEcology Space Food Shelter Temperature Mates Pollution Disease Limiting Factors • Any essential resource that is in short supply • All limiting factors acting on a population dictate sustainable population size

17. PopulationEcology 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. PopulationEcology 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

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

20. PopulationEcology Overshooting Capacity • Population may temporarily increase above carrying capacity • Overshoot is usually followed by a crash; dramatic increase in deaths Fig 40.7

21. PopulationEcology Resetting the Carrying Capacity • Major changes in environment can change the carrying capacity of a local system Fig 40.6

22. PopulationEcology 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

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

24. PopulationEcology Life History Patterns • Patterns of timing of reproduction and survivorship • Vary among species • Summarized in survivorship curves and life tables

25. PopulationEcology Life Table • Tracks age-specific patterns • Population is divided into age categories • Birth rates and mortality risks are calculated for each age category

26. PopulationEcology Survivorship Curves Fig 40.8

27. PopulationEcology 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

28. PopulationEcology Human Population Growth Fig. 40.9, p. 695

29. PopulationEcology How Humans have Side-Stepped density dependent controls • Expanded into new habitats • Agriculture increased carrying capacity; use of fossil fuels aided increase • Hygiene and medicine lessened effects of density-dependent controls

30. PopulationEcology Population Momentum • Lowering fertility rates cannot immediately slow population growth rate. Why? • If every couple had just two children, population would still keep growing for another 60 years Future Growth • Exponential growth cannot continue forever • Breakthroughs in technology may further increase carrying capacity • Eventually, density-dependent factors will slow growth

31. PopulationEcology 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

32. PopulationEcology 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

33. PopulationEcology 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

34. Community Ecology Community Ecology • Community: Populations of all species in a habitat. • Niche: Sum total of all a species activities and relationships as species do what they do. • Fundamental, Realized

35. Community Ecology Types of Interactions Who benefits? Spp 1 Spp 20 0Y 0Y YN NY NY N • Neutral • Commensalism • Mutualism • Competition • Predation • Parasitism

36. Community Ecology Competition • Competitive Exclusion • Paramecium • Resource Partitioning • Fruit eating birds, Barnacles

37. Community Ecology Predator-Prey Interactions • The Classic Lynx / Hare system

38. Ecosystems Ecosystems • Energy is transferred from the SUN to all organisms • Primary Producers • Consumers • Decomposers • Energy is LOST with each transition

39. Ecosystems Food Webs • A composite picture of an ecosystem’s membership and their interaction Fig. 43.6, p. 740 Do not post photos on Internet

40. Ecosystems Food Webs can be Disrupted • Natural Disasters • External inputs • Pesticides, Pollution

41. Ecosystems The Hydrologic Cycle Fig. 43.14, p. 746

42. Ecosystems Other Cycles • Carbon • Nitrogen • Phosphorus

43. Quiz