Carrying Capacity 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.
DISCUSSION QUESTIONS 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?
CASE STUDY - GYE ELK • 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.