It is the ambience, not the menu. Prey availability does not drive habitat selection by the endangered Pyrenean desman

Abstract

1. The Pyrenean desman (Galemys pyrenaicus) is an endangered stream-dwelling insectivore endemic to the Iberian Peninsula and the north of the Pyrenees. It favours riffles over slow habitats such as runs or pools, yet it is still unclear whether habitat preference is based on prey availability or on other factors, such as mechanical constraints on its hunting habits. 2. Desman diet and prey selection were analysed along the pristine Elama Stream and the slightly modified Leitzaran Stream in the Basque Country, Spain.3. In each stream the prey consumed were identified by metabarcoding 94 desman faeces, and prey availability characterized from 10 Surber samples taken in each habitat type (riffles, runs and pools). Invertebrates were sorted and identified, the biomass of each taxon was calculated, and their DNA was also extracted, amplified using PCR, and sequenced to build a reference database. 4. Prey availability and diet varied between streams. Desmans positively selected shredders and invertebrates that live on the substrate, and selected against taxa that live in fine sediment, taxa with hard shells or those that are highly mobile.The diet of desmans was more selective in the Elama, the stream with better ecological status. Food availability did not differ among habitats, and therefore does not explain the preference of desmans for riffles; rather, mechanical constraints to deal with buoyancy and physical habitat heterogeneity were hypothesized to be the reason behind the habitat preference.5. The results suggest that promoting the formation of riffles in streams can improve the situation of some desman populations living in degraded habitats.

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

“…Both mammals avoided the soft-bodied taxa that inhabit fine sediments (e.g. Athericidae, Limoniidae and Oligochaeta), a finding also reported in other studies of G. pyrenaicus (Esnaola et al 2021). This situation illustrates the interspecific trophic competition occurring between G. pyrenaicus and the other analysed semi-aquatic predators, as well as the partial prey overlap, in which these predators coexist by frequenting a different microhabitat determined by their specific morphological and physiological adaptations (Castién and Gosálbez 1999;Churchfield and Rychlik 2006).…”

“…In this aquatic environment, the Pyrenean desman outcompetes both N. fodiens and C. cinclus. Although its avoidance of terrestrial prey observed in the Catllar stream matches other studies that have used a morphological approach for prey identification (Santamarina 1993;Bertrand, 1994;Castién and Gosálbez 1999), some studies based on a genetic approach (Biffi et al 2017a, b;Esnaola et al 2021) indicate that the desman actively consumes terrestrial groups. Both these approaches permit the identification of a wide range of prey items but it is, nevertheless, important to understand the biology of these prey species when assessing their use as food resources to avoid misleading interpretations.…”

“…The Pyrenean desman is considered a generalist that feeds on the most abundant prey (Biffi et al 2017a;Hawlitschek et al 2018;Esnaola et al 2021) and only a few studies have ever reported a specialist diet for this species (Bertrand 1994). In our study, G. pyrenaicus focussed on aquatic, energetically profitable prey.…”

“…For instance, in many recent studies (Biffi et al 2017a, b;Esnaola et al 2021), the Diptera family Psychodidae has been reported to be an important component of the diet of the Pyrenean desman. In our study, individuals of this family were found in the analysed faecal samples but were also observed alive in faeces and later identified at the larval stage with no signs of having been digested.…”

“…for Trichoptera, Ephemeroptera and Plectoptera found in riffle sections of streams (Bertrand 1994;Santamarina 1993; Castién and Gosàlbez 1999;Esnaola et al 2018). Whilst some authors indicate that it also consumes a substantial amount of terrestrial prey (Gillet 2015;Biffi et al 2017a;Esnaola et al 2021), others suggest that in fact it consumes very little such prey (Santamarina 1993;Bertrand 1994;Castién and Gosálbez 1999;Hawlitschek et al 2018).…”