Body Size, Insectivory and Abundance in Assemblages of Small Mammals

Data from twenty five assemblages of small mammals are studied. There is no tendency for the species in the assemblages to show any predictable correlation between body mass and abundance. The same is true within the insectivore guild of each assemblage. However, assemblages nearer the equator have insectivore guilds with predictably more positive mass-abundance patterns than those at high latitudes. A survey of twenty years of the published literature reveals that in general, niche overlap in co-occurring small insectivorous mammals is lowest at high latitudes. If high niche overlap is associated with strong competition, this result may explain the patterns in abundance; positive mass-abundance correlations may be found where interspecific competition is most intense.