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CARRYING CAPACITY (K) - The population density where births and deaths are equal and population size is constant.

- This is ultimately set by limiting factors:
- shortages of resources (food, space, water), extreme conditions (cold temperature), physiological disruptions (predation, disease).

Density-dependent Population Regulation

--case were birth rate and/or death rate varies with population density.

Density-dependent Population Regulation

Intraspecific competition - competition among members of a population.

Interference competition - direct interactions among individuals where one individual prevents another from gaining access to a resource.

Interference competition: Territoriality

Numbers of breeding females on island

Density-dependent reproduction in a population of song sparrows on Mandarte Island, BC, Canada (from Arcese & Smith 1988). Squares denote data for each year from 1975-1986. Notice how reproduction increased in 1985 for pairs where food was provided.

Density-dependent Population Regulation

Intraspecific competition - competition among members of a population.

Interference competition - direct interactions among individuals where one individual prevents another from gaining access to a resource.

Exploitation competition - individuals consume a resource making it less available to other individuals

SELF THINNING - process where by some plants out compete others leading to more and more biomass being concentrated in fewer and fewer individuals.

DENSITY-INDEPENDENT POPULATON REGULATION - Rates (per individual) of birth and/or death do not vary with population density.

E.g., fire, flood, volcano, etc.

What are possible examples of density-independent factors regulating ungulates in YNP?

How might density-independent and density-dependent factors interact to influence populations of ungulates in YNP?

- Coughenour, M. B., F. J. Singer. 1996. Elk Population Processes in the Yellowstone National Park Under the Policy of Natural Regulation. Ecological Applications 6, no. 2 : 573-93.

Regression between precipitation and winter mortality rates of elk calves. (Cougenhour and Singer 1997).

CONCLUSIONS: POPULATION REGULATION IN REALITY

1. K is usually a moving target, so a population stays within a range of variation.

2. Density independent factors may keep population size below K, and cause variation in population size.

3. Time lags and density dependent controls may cause population cycles.

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