A reproductive strategy where survival of a species is optimised by placing a premium on individual survival despite fluctuations of the environment. Favors large animals (and large animals favor this strategy) -- animals that get pregnant more than once and the offspring of which require postnatal care before sexual maturity is reached. Spacing of pregnancy is important for survival of mother and offspring, and thus favors the evolution of a genetic basis for subfertility. The opposite reproductive strategy to r-selection. The word comes from the environment's Karrying capacity.

A reproductive strategy where survival of a species is optimised by explosive increases in numbers of animals whenever environmental circumstances are favorable; typically seen with small animals that reach sexual maturity quickly, which reproduce just once but with many progeny, and which do not need to tend to their progeny for very long (if at all) after birth. In extreme cases (seen in many lower animals such as insects), death of the father follows impregnation and death of the mother follows parturition (or giving birth). The opposite reproductive strategy to K-selection.