Differentiation of activity rhythms and space use between two competing water shrew species in a laboratory experiment

Abstract

Hypothesesabout the differentiation of activity rhythms and space use between two competing species of water shrews, Neomys anomalus [AA] and N. fodiens [FF], were verified in a laboratory experiment. The animals were kept together for 2 months in an enclosure (195 × 145 cm) and their activity was video recorded using the time-lapse mode. Changes in activity rhythms, distances kept between active animals, and frequency of interspecific conflicts were compared between the early (first 24 h) and late (last 24 h, after 2 months) phases of the animals’ coexistence in the mixed group. In both phases, the activity of both species was relatively evenly distributed over 24 h, with breaks in activity nearly every 1 h. During the early phase, both species were equally and simultaneously active, whereas in the late phase, as predicted, the activity of FF was lower than that of AA, and asynchronous. In the late phase, pairs of different species (F-A) were rarely active simultaneously and kept long inter-individual distances. Consequently, the number of conflicts decreased. The results suggest that, over time, water shrews can develop mechanisms diminishing interference competition, which are based on shifts in activity rhythms, maintaining distance between individuals, and the rare usage of the same shelters and feeding sites.