R/K selection theory

r/K selection theory describes the way a species controls its number of offspring. 
r-selection species produce many offspring. K-selected species focus on a few. Neither method is in itself superior, and they may occur in the same habitat; e.g., rodents (r-selection) and elephants (K-selection). 
The theory was popular in the 1970s and 1980s, but several studies criticized it. The study of life histories has replaced the r/K selection paradigm.
The terminology of r/K-selection was coined by the ecologists Robert MacArthur and E.O. Wilson, based on their work on island biogeography. Study of the evolution of life history strategies actually has a longer history.