Difference in diet as an epiphenomenon: space regulates salamanders

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Abstract
Observations on prey size and spatial dispersion of two plethodontid salamanders widely sympatric in California suggest that food resources do not regulate the densities of the salamanders and hence are not the critical resource for their coexistence. Competition may still occur for limited food resources but such competition may influence only relative size or fecundities of the species and not their densities. Observations are consistent with the hypothesis that spatial resources regulate salamander densities. These observations include the following (1) when large prey is scarce the larger Aneides lugubris can consume smaller prey efficiently (as a consequence, its diet overlaps almost completely that of the smaller Batrachoseps attenuatus); (2) size groups that overlap most in diet also overlap most in space; (3) individuals of Batrachoseps seem to be distributed with respect to spatial rather than food resources since large differences in fatness and stomach size among individuals occur within small areas of continuous habitat; and (4) the abundance of Aneides relative to Batrachoseps is greatest in habitats with the greatest abundance of large cavities that adult Aneides can use for protection. The above observations are relevant to the general problem of competition for size-dependent resources between microsympatric vertebrate insectivores.