What is Life-history strategies?

Species differ in where they sit between two extremes. A $r$-selected species — weeds, aphids, mice, most fish — is built for a high $r$: it matures early, produces many small offspring, invests little in each, lives briefly, and exploits new or disturbed habitats before the competition arrives, with a type III survivorship. A $K$-selected species — oaks, elephants, albatrosses — is built to persist near $K$: it matures late, produces few large offspring, cares for them, lives long, competes well in crowded stable habitats, with a type I curve. Most species mix the two; the labels name the ends of the scale.