In nature, organisms with two fundamentally different life strategies can be encountered. The difference between an R-selected species and a K-selected species is that the R-selected species live in variable, unstable habitats, while K-selected species reside in stable environments. In r/K selection theory, selective pressures are hypothesised to drive evolution in one of two stereotyped directions: r- or K-selection. One group of organisms prefers rapid reproduction.
Sea turtles are a good example of a species that fits somewhere in the middle. The name is based after variables in an equation used by MacArthur and Wilson that relates the growth rate of various organisms to the carrying capacity of the environment. The model of r- and K-selection, also presented as the model of r- and K-strategy, was a popular concept of field ecology in their time (Pianka 1970). R-selected species produce many offspring, but only a few live out their lifespan. The r/k selection theory should be thought of as a spectrum. R/K selection theory is a popular ecological theory developed by Robert MacArthur and E. O. Wilson from their 1967 work on island biogeography. Its members are called r-strategists and the natural K-selected species have a few offspring that have a long life expectancy. Some organisms may produce a medium number of offspring but those offspring still grow quickly and the parents provide little care. These terms, r and K, are derived from standard ecological algebra, as illustrated in the simple Verhulst equation of population dynamics: $ \frac{dN}{dt}=rN\left(1 - \frac{N}{K}\right) \qquad \!
r selection is a method of rearing offspring with an emphasis on high growth rate and population increase (explanation shows comparison to K selection) r and K selection refer to the selection of the combination of traits in an organism relating to how they rear their offspring.