Effects of Predation and Competition on Survivorship, Fecundity, and Community Structure of Desert Annuals

Abstract

Effects of rodent and ant granivores, watering, and thinning were studied in a diverse community of winter annuals in the Sonoran Desert. Seed predation considerably reduced plant densities, but ants and rodents had qualitatively different effects on the plant community. Ants increased species diversity of annuals by differentially harvesting the numerically dominant species, while rodents preyed selectively on species which dominated the community in terms of biomass. Competition among annual plants reduced growth rate, biomass, and fecundity, but had no significant effect on mortality. One species, Euphorbia polycarpa, apparently increased in density when the density of competing Erodium species was reduced by rodent predation.