In ecology, r/K selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring

r-selectedK-selected
many offspring, low investmentfew offspring, high investment
thrive in unstable habitatsthrive in stable habitats

r-selection

r-selected species are those that emphasize high growth rates, typically exploit less-crowded ecological niches, and produce many offspring, each of which has a relatively low probability of surviving to adulthood

Examples include dandelions, insects, rodents, etc.

K-selection

K-selected species display traits associated with living at densities close to carrying capacity and typically are strong competitors in such crowded niches, that invest more heavily in fewer offspring, each of which has a relatively high probability of surviving to adulthood

Examples include elephants, humans, whales, etc.