R and k selection.

soil microbiology

1. R and K Selection

2. R and K selection means: The two evolutionary "strategies" are termed r-selection, for those species that produce many "cheap" offspring and live in unstable environments. K-selection for those species that produce few "expensive" offspring and live in stable environments.

3. Difference between R and K selection The r selected species live in populations that are highly variable. The fittest individuals in these environments have many offspring and reproduce early. In K selected species, population size are often small, and therefore, individuals run a high risk of inbreeding.

4. Characteristics of organisms which are extreme r or K strategists r Unstable environment, density independent k Stable environment, density dependent interactions small size of organism large size of organism energy used to make each individual is low energy used to make each individual is high many offspring are produced few offspring are produced early maturity late maturity, often after a prolonged period of parental care short life expectancy long life expectancy each individual reproduces only once individuals can reproduce more than once in their lifetime type III survivorship pattern in which most of the individuals die within a short time but a few live much longer type I or II survivorship pattern in which most individuals live to near the maximum life span

5. The terms r and k are derived from the logistic equation for growth of a population (Andrews 1991)