Coexistence of the Water Shrew (<i>Neomys fodiens</i>) and the Common Shrew (<i>Sorex araneus</i>), the Competing Species, in a Flucturing Environment: Sociability and Space Use in a “Dry” Habitat

Abstract

Sustainable (no trend in the abundance of interacting species) coexistence of species can be maintained due to fluctuations in their abundance and distribution over habitats in a heterogeneous environment. In the water shrew and the common shrew, joint settlements exist in near-water areas and occasionally appear in “dry” habitats, where the water shrew periodically invades. Given the well-known overlapping food niches of these species, one would expect the discovery of mechanisms that reduce competition, however, in “dry” habitats, we did not find such mechanisms. The use of space is characterized by a random overlapping of the home ranges of animals. In the preference test (a container with an animal versus an empty container), individual repeatability of sociability was found in tests with a conspecific stimulator, but was absent in tests with a stimulant of another species. The presence of the water shrew (as a stimulant) in the behavioral test did not increase of anxiety of common shrews, but increased the thoroughness of exploration. The reaction of the water shrew to the common shrew was not found in interspecific tests. In the absence of specific adaptations aimed at the spatial segregation of animals, the coexistence of the water shrew and the common shrew is quite well explained by “fluctuation-dependent” models of coexistence.