Trophic competition in a guild of insectivorous semi-aquatic vertebrates in a Pyrenean headwater stream: diet specialisation in the endangered Galemys pyrenaicus

Abstract

Conservation of vulnerable species in headwater streams requires good knowledge of their resource use and how they interact with competitors. In this study, we characterised the macroinvertebrate community of a Pyrenean headwater stream and assessed how it was used as a food resource—above all, in terms of prey electivity and diet overlap—by three semi-aquatic insectivorous vertebrates (Galemys pyrenaicus, Neomys fodiens and Cinclus cinclus). With this information, we examined the diet specialisation of the vulnerable Pyrenean desman (G. pyrenaicus) in the stream and analysed its implications for its conservation. There was a clear dietary overlap between these three predators, which resulted in interspecific trophic competition. G. pyrenaicus tended to avoid terrestrial prey and focused on abundant and energetically profitable rheophile species, for which it is well adapted. This diet specialisation makes it vulnerable to any decrease in food availability resulting from anthropogenic stressors such as damming, which can reduce habitat quality and prey availability. More research is needed to fully understand prey electivity in G. pyrenaicus and so be able to suggest effective conservation measures for this species.