Assessment of the distribution of Pseudoryzomys simplex (Cricetidae, Sigmodontinae) in the Pampean region, central-east Argentina, in the late-Holocene

Pseudoryzomys simplex (Winge 1887) is a small to medium sized terrestrial oryzomyine rodent (Cricetidae, Sigmodontinae) widely distributed in humid environments of tropical and subtropical lowlands of South America with a marked rainy season. The occurrence of this species in the south-central Pampean region between 4700 and 200 ka cal BP was originally associated with some warm climatic episodes. A later hypothesis points out that P. simplex was a typical element of the Humid Pampa subregion during this period, whose distribution was retracted to the north due to the strong anthropic modifications in the area. To corroborate these hypotheses, the niche of occurrence of P. simplex was calculated to analyse the preferred climatic conditions of contemporaneous and fossil record of the species since 4700 ka cal BP. The derived climatic niche of P. simplex shows a marked preference for areas with seasonality precipitation patterns and tropical/subtropical conditions. Geographical estimations and climatic niches derived revealed a moderate overlapping between contemporaneous and Pampean late-Holocene projection, which in no case includes the localities where fossil data were found. Although a better comprehension of the ecological requirements of the species is necessary to discard a shift in its realized climatic niche, it is probable that P. simplex is able to maintain stable populations under similar conditions to the ones represented by fossil occurrences. The distribution of the species in the Humid Pampa subregion is probably affected by non-climatic factors today which are reducing its contemporaneous realized climatic niche and distorting the derived climatic niches obtained. These results support that this species cannot be considered a reliable palaeoclimatic indicator of more Brazilian conditions in the Humid Pampean subregion during the past.