Genetic diversity and the r/K gradient in animals.
The average per-day fecundity is on the x axis and the average size of eggs or juveniles is on the y axis; each dot is for a family (one to four species each). The colour scale indicates the average nucleotide diversity at synonymous positions, expressed in per cent. The negative correlation reflects a trade-off between quantity and size of offspring. r-strategists (bottom right; for example, blue mussels, heart urchins and lumbricid earthworms) are more polymorphic than K-strategists (top-left; for example, penguins, Galapagos tortoises and subterranean termites).