Spatial segregation between the water opossum Chironectes minimus and the water rat Nectomys squamipes: Just competition avoidance or a conservation problem as well?

Riparian zones, as spatially constrained environments, can favor intense competition among similar species and thus the occurrence of spatial segregation. We investigated the spatial pattern of water opossum Chironectes minimus and water rat Nectomys squamipes captures in Atlantic Forest rivers in southeast Brazil. Our goals were to test if the water opossum and water rat are spatially segregated, to describe the habitat selection by these two species and to verify if habitat degradation favors the water rat, at the expense of water opossum. The abundances of water opossum and water rat were negatively correlated. Water opossum abundance was higher in wide rivers with high tree density in the riverbank, while water rat abundance was higher in narrow streams within non-forested areas. The ratio between the water opossum and water rat relative abundances was positively related to the degree of conservation of the riverine habitat. The segregation showed by the water opossum and the water rat was produced by their morphological and ecological differences, rather than by interespecific competition. Based on ours results we predict that deforestation, especially the removal of riparian vegetation, will result in a reduction of the suitable habitat for the water opossum while the water rat will expand its range.