R/K Selection Theory
Overview
The r/K selection theory is a model in population ecology that classifies species into two broad categories based on their life history strategies. The theory is named after the ecological terms 'r' and 'K', which denote the intrinsic rate of natural increase of a population and the carrying capacity of an environment respectively. The theory was first proposed by the ecologists Robert MacArthur and E.O. Wilson in 1967, and has since been applied to various fields including evolutionary biology, psychology, and sociology.
R-Selection
R-selected species are those that emphasize high growth rates, typically exploiting less-crowded ecological niches, and producing many offspring, each of which has a relatively low probability of surviving to adulthood. These species are often characterized by short gestation periods, early maturity, high fecundity, and short lifespan. Examples of r-selected species include bacteria, rodents, and insects.
K-Selection
In contrast, K-selected species display traits associated with living at densities close to carrying capacity, and typically are strong competitors in such crowded niches that require more resources. They are characterized by long gestation periods, delayed maturity, low fecundity, and long lifespan. Examples of K-selected species include elephants, humans, and whales.
R/K Continuum
The r/K selection theory proposes a spectrum of reproductive strategies between the r-selection and K-selection extremes. Species do not fall neatly into either category, but lie somewhere on the continuum based on their life history characteristics. This continuum is influenced by various factors such as environmental stability and resource availability.
Criticisms and Modifications
While the r/K selection theory has been influential in shaping our understanding of life history evolution, it has also faced several criticisms. Some critics argue that the dichotomy between r and K selection oversimplifies the complex nature of life-history evolution. Others point out that the theory does not account for the influence of age-specific mortality, which has led to the development of the age-specific mortality model.
Applications
Despite its criticisms, the r/K selection theory has found applications in various fields. In evolutionary biology, it has been used to explain the evolution of different life history strategies. In psychology, the theory has been applied to understand human behavior and personality development. In sociology, it has been used to analyze social and demographic trends.