R/K Selection Theory

In ecology, r/K selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring. The focus upon either increased quantity of offspring at the expense of individual parental investment, or reduced quantity of offspring with a corresponding increased parental investment, varies widely, seemingly to promote success in particular environments. In this context, r-selection makes a species prone to numerous reproduction at low cost per individual offspring, while K-selected species expend high cost in reproduction for a low number of more difficult to produce offspring. Neither mode of propagation is intrinsically superior, and in fact they can coexist in the same habitat, as in rodents and elephants.

The theory was popular in the 1970s and 1980s when it was used as a heuristic device, but lost importance in the early 1990s as it was criticized by several empirical studies. The r/K selection paradigm has been replaced by a "life-history" paradigm. However, this continues to incorporate many of the themes important to the r/K paradigm.

The terminology of r/K-selection was coined by the ecologists Robert MacArthur and E. O. Wilson based on their work on island biogeography.