Variações na abundância de roedores (Rodentia, Sigmodontinae) em duas áreas de floresta ombrófila mista, Rio Grande do Sul, Brasil

Vargas Cademartori, CristinaElena Fabián, MartaOldair Menegheti, João

The composition and abundance fluctuations of Oligoryzomys nigripes (Olfers, 1818), Akodon montensis Thomas, 1913, Delomys dorsalis (Hensel, 1872) and Oryzomys angouya Fisher, 1814 were studied from August 1992 to August 1993 in two areas of mixed forest with conifers at National Forest of São Francisco de Paula (2923S, 5023W), southern Brazil. Seven bimestrial trappings were carried out in each study area. Two grids of 60 traps were exposed simultaneously during five nights in each trapping period. The highest abundance indexes occurred in August 1992 and August 1993, just on the final stage of seed production by Araucaria angustifolia. Such observations, more evident for O. nigripes and A. montensis, point out that populations of these species increased when there were many A. angustifolia seeds on the floor. The high abundance indexes exhibited by A. montensis in August 1992 and August 1993 can be explained by recruitment. D. dorsalis seems to be the most habitat selective species because of the low abundance indexes that were found in the area with high densitiesof A. angustifolia. O. angouya was recorded occasionallyand always in low levels of abundance in both study areas. The presence of these species, in spite of low abundance indexes, during the stage of seed production by A. angustifolia in the forest, points out that resource availability indeed increases at this