What is r/K selection theory?

This theory was more popular in the 1970's and has lost some favor because of the inability to test it.

K-selected species expend high cost in reproduction for a low number of more difficult-to-produce offspring.

"A North Atlantic right whale with solitary calf. Whale reproduction follows a K-selection strategy, with few offspring, long gestation, long parental care, and a long period until sexual maturity."

r-selection makes a species prone to numerous reproduction at low cost per individual offspring. This would be seen in rodents with many offspring. short gestation, short parental care and a short time until the off spring can reproduce.

Reptiles and turtles have both r and K while male humans have r and females have K. It is thought that K species will replace r species in what is called a climax ecosystem.