R/K selection theory

The r/K selection theory is an evolutionary hypothesis examining the selection of traits in an organism that trade off between quantity and quality of offspring. Species which produce more offspring at the expense of reduced individual parental investment are termed r-strategists, while those which make greater parental investment at the expense of a reduced quantity of offspring are termed K-strategists. The occurrence of the two varies widely, seemingly to promote success in particular environments. The concepts of quantity or quality offspring are sometimes referred to in ecology as "cheap" or "expensive", a comment on the expendable nature of the offspring and parental commitment made. The stability of the environment can predict if many expendable offspring are made or if fewer offspring of higher quality would lead to higher reproductive success. An unstable environment would encourage the parent to make many offspring, because the likelihood of all (or the majority) of them surviving to adulthood is slim. In contrast, more stable environments allow parents to confidently invest in one offspring because they are more likely to survive to adulthood. The terminology of r/K-selection was coined by the ecologists Robert MacArthur and E. O. Wilson in 1967 based on their work on island biogeography; although the concept of the evolution of life history strategies has a longer history (see e.g. plant strategies). The theory was popular in the 1970s and 1980s, when it was used as a heuristic device, but lost importance in the early 1990s, when it was criticized by several empirical studies. A life history paradigm has replaced the r/K selection paradigm, but continues to incorporate its important themes as a subset of life history theory. Some scientists now prefer to use the terms fast versus slow life history as a replacement for, respectively, r versus K reproductive strategy.