Climate change at a tropical-subtropical interface: long-term changes in sigmodontine community structure in the Upper Paraná Atlantic Forest, Paraguay

Abstract

Long-term studies are fundamental for documenting and understanding the effects of climate change on small mammal communities, especially in regions of ecoregional boundaries and the interface between tropical and subtropical biota. Moreover, such studies are best conducted in areas not experiencing changes in land use / land cover, to avoid confounding the effects of these changes with those of longer-term climate change. The Reserva Natural del Bosque Mbaracayú, in northeastern Paraguay, is located near the western extreme of the Interior Atlantic Forest and <1° from the Tropic of Capricorn. The forests in the reserve have been protected for 30 years and were largely undisturbed prior to creation of the Reserve. Intensive sampling of small mammals was conducted several times over a period of 22 years (1996-2017), during which time average annual temperature has risen by about 0.4° C and annual precipitation has increased by about 140 mm. Evaluating each of the three predominant sigmodontine species over 22 years reveals a signifcant increase in proportional abundance of the tropical species Hylaeamys megacephalus in the rodent community, and a shift from third to second most abundant rodent species during that time. The other two abundant sigmodontine species (Akodon montensis and Oligoryzomys nigripes) have distributions that include considerable subtropical areas. Their proportional abundance showed very little change during the study, and “other” (the remaining sigmodontine species) decreased somewhat. This is the first documentation of increased proportional abundance over time of a tropical rodent in a tropical-subtropical sigmodontine community.