K-Selected and r-Selected Species

Every species splits a limited reproductive budget between offspring number and offspring care. An r-selected species spends that budget on quantity: short generation time, early sexual maturity, huge litters or seed crops, and little or no care per offspring. A dandelion releases roughly a thousand seeds and walks away from all of them. A K-selected species spends the same budget on quality: long generation time, late maturity, one or two offspring at a time, and years of feeding, teaching, or protecting each one. An elephant has a single calf roughly every four or five years and guards it for over a decade.

The letters come from the logistic growth equation. r is the intrinsic growth rate, so r-selected species are built to grow population size fast when space and resources are open. K is carrying capacity, so K-selected species are built to hold a population steady near the ceiling a habitat can support. That link to the population curves matters: r-selected growth traces a J-shaped curve, booming unchecked until something crashes it, while K-selected growth traces an S-shaped curve that levels off smoothly as the environment fills up.

Neither strategy is a flawed version of the other. r-selection wins in unstable, open, or disturbed habitats where conditions change fast and getting there first beats surviving long. K-selection wins in stable, crowded habitats where competition for limited resources rewards investing heavily in offspring that can outcompete others. A clearcut hillside shows this directly: the bare, resource-rich, competition-free ground favors fast colonizers first, before slower, better-competing species move in later.