Weak evidence of spatial segregation between the vulnerable southern water vole (Arvicola sapidus) and the two main invasive mammals of European freshwater ecosystems

Niche differentiation by spatial segregation facilitates the coexistence of species sharing ecological preferences, which can buffer the impact of biological invasions on native species. The introduction of two semi-aquatic rodents, the coypu Myocastor coypus and the muskrat Ondatra zibethicus, to most freshwater ecosystems across Western Europe, has been pinpointed as a cause for the decline of the southern water vole (SWV) Arvicola sapidus. We investigated the co-occurrence of these three species in a river catchment of northwest France and whether spatial habitat segregation took place at two spatial scales, using hierarchical modelling accounting for imperfect detection. At a large spatial scale (river catchment), the occupancy rate of the SWV was 0.52 +/- 0.06, i.e. noticeably smaller compared to coypu (0.58) and muskrat (0.80). We found no evidence of a negative effect of the presence of the two invasive rodents on SWV occurrence. At a smaller spatial scale (SWV home range), we found weak evidence of spatial segregation in habitat use with a negative, although not significant, effect of muskrat. Overall, our results suggest that riparian habitats in the study area allow the southern water vole to coexist with two larger invasive rodents, provided that hygrophytic vegetation is preserved alongside rivers.

Automated summary

Spatial segregation allows species with similar ecological preferences to coexist, potentially mitigating the impact of biological invasions. In a river catchment in northwest France, the southern water vole, coypu, and muskrat were found to coexist without a negative effect of the two invasive rodents on the water vole. Weak evidence of spatial segregation at a smaller scale was observed, with a non-significant impact of muskrat on the water vole.