CPES Ecology Part II Population Ecology

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?

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

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 added is 6000

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

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

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

The J Curve - exponential growth

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”

Carrying Capacity

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)

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

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?

Example of Irruptive Growth

Malthusian or Irruptive Growth

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?

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?

Moose and Wolves of Isle Royale

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?