The r and K classification was originally proposed by the biologists Robert McArthur and E. O. Wilson (1967).
A good way of thinking about K selected species is to think of a mature forest tree. It exists in non disturbed native forest habitats. Forest trees grow slowly and reach reproductive age late, having to devote much energy to growth and maintenance. K selected species grow large and shade out r selected species, eventually out competing them. Such trees live a long time and produce seeds repeatedly every year when mature. These seeds are bigger than those of r selected species.
Example of K selected tree such as sequoia, large terrestrial animal such as elephant, rhinoceros, and grizzlies and large marine mammals such as blue whales and sperm whales.