Seed predation in the legume Crotalaria : I. Intensity and variability of seed predation in native and introduced populations of C. pallida ait

Abstract

In order to evaluate the role of seed predators as selective agents within a population of conspecific plants, the intensity of predispersal seed predation by chewing insects and the variation in predation intensity with individual and season were measured for the legume shrub Crotalaria pallida. In a native, tropical (East African) population, predation intensity averaged 49% for late dry season-early wet season samples, but ranged from less than 20% to near 100% for different individuals. Average seedcrop loss varied markedly with season, and these seasonal shifts differed in two adjacent sites, probably due at least in part to transient predator satiation. However, individual plants differed significantly in intensity of seed predation sustained, and these individual differences were apparently maintained consistently in the face of the seasonal changes. For introduced, temperate-zone (North Carolina, USA) populations of the same species, predation averaged only 16-17%, but the proportionate variation among individuals was even greater than for the African population. These results support the hypothesis that predators inflict substantial differential seed mortality and discriminate consistently among individual plant seedcrops, thus exerting strong selection within plant populations.