Food niche overlap and ecological separation amongst six species of coexisting forest shrews (Insectivora: Soricidae) in the Russian Far East

The feeding habits and foraging modes of six species of shrew (Insectivora, Soricidae) coexisting in the forests of the Russian Far East were investigated in order to quantify levels of niche overlap and elucidate the role of body size in ecological separation. Overlap in numbers of shared prey taxa was high and Lithobiomorpha, one of the most abundant macro-invertebrates in field samples, was a major prey item of all species. The composition of different prey taxa in the diet of Sorer unguiculatus and the abundance of these taxa in field samples were positively correlated. Major differences in dietary composition and foraging mode reflected body size of shrews. While the niches of individual species were not exclusive, small species fed only on arthropods, were epigeal, and had relatively narrow niche breadths. Large species fed extensively on lumbricids and other soil-dwelling invertebrates, and were hypogeal. There were significant negative correlations between niche overlap in terms of prey composition, prey size and prey location, and increasing body-length ratios in pair-wise comparisons. Combined niche overlap was reduced with increasing divergence of body size. Adjacent species-pairs in the size series had a mean combined niche overlap of 88% compared with non-adjacent pairs of 67%. The most significant areas of ecological separation between species as a function of body size were in the dietary occurrence of small versus large prey and in the foraging mode (epigeal versus hypogeal). These findings confirm that body size has an important role in effecting ecological separation in multi-species communities where a high degree of morphological and ecological similarity occurs between members.