Among biological organisms, there is a continuum in life history strategies between what are referred to as r-selected species and k-selected species. Life history strategy is correlated with many aspects of an organism's reproductive strategy and life history, as well as with demographic variables such as generation time and life span, and population parameters such as population density and population dynamics. Where individual species fall on the r-k continuum is largely determined by the environment in which they live.

The variables r and k in r-and k-selection come from the logistic equation for population growth. This equation describes how population density changes over time. In the initial phase, population growth is very rapid and largely dependent on the variable r, which represents the intrinsic rate of natural increase of a species. Mathematically, r is the birth rate plus the immigration...