Effects of climate and food availability on four rodent species in southeastern Brazil

Seasonal reproduction of small mammals in the tropics usually is related to annual cycles of rainfall. We examined effects of weather and food availab ility on reproduction and population ecology of Nectomys squamipes, Oryzomy s intermedius, Akodon cursor and Trinomys iheringi. Each species was studie d monthly from February 1993 to January 1995 using mark-recapture methods a t Ilha do Cardoso, Sao Paulo State, Brazil. Average capture rate for each m onth was used as an index of population size, and survival rate was estimat ed by the Jolly-Seber method. Direct effects of food availability and rainf all were related to female reproductive activity and survival rate. Path an alyses were used to describe quantitatively the hypothesized causal relatio ns among the variables. N. squamipes reproduced seasonally, and O. intermed ius, T. iheringi, and A. cursor reproduced all year with peaks during the r ainy season. Species responded differently to the environmental factors; ho wever, food availability seems to be the main factor determining reproducti on, Abundance of rains appears to diminish survival rate of O. intermedius. Survival rate of N. squamipes increases with increases in fruit availabili ty.