Niche partitioning and coexistence between two mammalian herbivores in the Dry Chaco of Argentina

Competitive interactions are known to be stronger between morphologically similar and phylogenetically closely related sympatric species. Patagonian mara (Dolichotis patagonum) and Chacoan cavy (Pediolagus salinicola) are two medium-sized herbivorous mammals which have disjunctive distributions within a sympatric region characterized by dry woodlands and shrublands (Dry Chaco, Argentina). The niche partition hypothesis predicts that ecologically similar species living together should show differentiation in at least one of the main niche dimensions to avoid competition. Thus, we predict that Patagonian mara and Chacoan cavies will differentiate in the use of trophic and/or spatial niche. To prove this hypothesis, we sampled 26 study sites in the dry and wet season and collected fresh faeces of both species. We estimated the diet composition using microhistological analysis of faeces. For habitat analysis we measured 16 vegetation variables, as well as habitat complexity and heterogeneity structure. Our results showed that during the dry season, both species segregate their diet but not their habitat niche, whereas during the wet season they segregate their habitat, and diet segregation is diffused. Diet overlap was similar between seasons, indicating a change in the foraging strategy of the cavy, which selected forbs, grasses, succulents and trees in the dry season and only grasses in the wet season. Our results support the niche partition hypothesis as a mechanism of coexistence among ecologically similar species in the South American temperate arid lands.