r-K Selection at Various Taxonomic Levels in the Pierine Butterflies of North and South America

Abstract

The theory of r and K selection (MacArthur and Wilson 1967) attempts to make very sweeping predictions about the life history traits of organisms evolving under different forms of population control; it has generated a large body of literature in which it has been tested observationally, experimentally, and mathematically. Many of the empirical tests have consisted of looking for evidence of r- and K-selected traits in populations of species along various gradients, of which the most common have been latitude, climatic predictability, and habitat stability (Cody 1966, 1971; Gadgil and Solbrig 1972; Abrahamson and Gadgil 1973; Solbrig and Simpson 1974; Gaines et al. 1974; Abrahamson 1975; McNaughton 1975; Derickson 1976). The gradients chosen were initially very simplistic (Pianka 1970): thus we find Krebs (1972, p. 579) saying: “The simplest illustration of these two extremes might be organisms in tropical (K selection) vs. polar environments (r selection).” Although we have become less naive, the initial suggestions of the 1970s persist in the minds of many ecologists. As a result, it is often assumed that populations in high latitudes are under density-independent regulation, whereas those in low latitudes are density-dependent. Yet most ecologists will readily admit that evidence bearing on this proposition is scarce at best, and even classic studies of population regulation are frequently subjected to reinterpretation. Needless to say,“validations” of r-K theory are potentially spurious when not supported by convincing studies of population regulation.