CPES Ecology Part II

1. CPES Ecology Part II Population Ecology 2008-09

2. Populations - Topics to be Discussed • Populations either • grow • decline • stay the same • What influences the growth of a population? • How does population size, density, and growth affect an organism’s environment?

3. Population Ecology Definitions • population • biotic potential • environmental resistance(limiting factors) • population density • carrying capacity • predators and prey • parasites and host • limiting factors • Density-dependent • Density-independent • competition • intraspecific • interspecific

4. Population Growth Rate • Birth Rate: births/popn at beginning • Death rate: deaths/popn at beginning • Growth rate = birthrate-deathrate • Example • Population of 5000 on Jan 1 • Births 400 throughout year • Deaths 100 throughout year • What is Birthrate and deathrate? • How many added to this population this year • Calculate number added if population were 100,000 at beginning of year instead of 5000 • Answers: BR=8%; DR =2%; GR=6% • Popn 100000 added is 6000

5. Rate of Growth – Births • What would affect number of births in a population? • Number of young in each “litter” • Examples of high and low number?? • How often have young • Examples of seldom vs. often • Age at which females start having young • Rodents vs. elephants

6. Rate of Growth – Deaths • What would affect number of deaths in a population? • Lifespan • Outside environmental factors – limiting factors

7. Population Growth Curves • Exponential growth • S-curve • Carrying capacity • limiting factors • Population explosions (11) - irruptive growth pattern

8. The J Curve - exponential growth

9. Exponential vs. Arithmetic Growth • Arithmetic: constant amount per time unit • Independent of population size • Exponential: increases by constant fraction, or exponent, by which current population multiplied • Actual number of organisms added dependent on population size • Power of biological reproduction • Rate constant, but number added changes: “Compound interest”

10. Carrying Capacity

11. Limiting factors affecting population - biotic or density dependent Food, predators, disease, human activity • bluebirds • predators and PA deer (8) • succession - PA forests and grouse (8) • habitat fragmentation • habitat loss • Case studies • Predators - a Natural Balance? (1.3) • The case of the missing hawks (1.4) • Coyotes - opportunistic omnivores (1.5)

12. Limiting factors affecting population - abiotic or density independent • Climate and weather • Soil (mineral components) • Slope (% and direction) • Oxygen content of water • Aquatic - type of bottom

13. Irruptive Growth • Rapid exponential growth (J curve) followed by population crash • Population surpasses carrying capacity • Death rate exceeds birthrate • Are there some organisms for which this is normal? • Yes! • What are some examples?

14. Example of Irruptive Growth

15. Malthusian or Irruptive Growth

16. Do some populations “limit” their own growth • Territoriality • Levels of fertility • may depend on food supply • Why might this be an advantage for the population? • What process may have resulted in such “intrinsic” limiting factors?

17. Predator and Prey Relationships • Do predators destroy a prey population, resulting in declines and possible extinction? • Do predators actually benefit the prey population? • What is the relationship between predators, prey, and habitat?

20. Moose and Wolves of Isle Royale

21. Isle Royale - Wolves and Moose • What caused 1930 crash in moose population? • Why did the moose not decrease their population before the crash occurred? • Why did the predators not exterminate the moose population? • What happened when the wolf population declined in the 1980s?