Ecological release: Swimming and diving behavior of an allopatric population of the Mediterranean water shrew

Abstract

In regions where the 2 species are sympatric, the Eurasian water shrew, Neomys fodiens, dominates behaviorally and numerically over the Mediterranean water shrew, Neomys anomalus, and tends to exclude it from direct access to aquatic habitats. In Portugal, ecological release can be expected in behavioral traits of N. anomalus due to the absence of the dominant N. fodiens. We investigated swimming and diving skills and efficiency in underwater foraging in 9 individuals of N. anomalus from Serra da Estrela, central Portugal. Efficiency in swimming and diving was analyzed in short-duration tests. Foraging behavior was assessed through video records of shrews foraging in a terrarium that simulated terrestrial and aquatic habitats. Our results were compared with data previously obtained for N. anomalus and N. fodiens coexisting in sympatry in Białowieża Forest, eastern Poland. In contrast to sympatric Polish N. anomalus, allopatric Portuguese N. anomalus were more efficient in some swimming parameters (such as stroking frequency) and showed greater variation in diving profiles. Allopatric N. anomalus also were able to take food from deep water, a behavior that previously had been observed only in N. fodiens. Foraging success underwater, however, was much lower in allopatric N. anomalus than in N. fodiens. Our results suggest that in the absence of the dominant N. fodiens, allopatric N. anomalus can use 2 foraging modes: wading in shallow water (its primary foraging mode) and diving in deep water, thus extending its ecological niche. © 2013 American Society of Mammalogists.