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

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. The water shrew and common shrew, coexist in near-water areas and occasionally in “dry” habitats, where the water shrew periodically invades. Given the well-known overlapping of 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 stimulant, 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 the anxiety of common shrews, but only increased the thoroughness of exploration. No reaction of the water shrew to the common shrew was 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.