Effects of weather and food availability on the condition and growth of two species of rodents in Southeastern Brazil

We studied the effects of food availability and rainfall on the condition and growth rates of Nectomys squamipes and Oryzomys russatus, at Ilha do Cardoso, Brazil. Condition and growth rate were estimated monthly from February 1993 to January 1995 using mark-recapature methods. Condition was calculated as the residual of the relationship between the natural locarithm of mass and the natural logarithm of head and body length. Size-independent,growth rate of the tail was estimated for N. squainipes and O. russatus. Size-independent growth rate was related to food availability and rainfall by multiple regression. Because multiple regression identifies only direct effects, path analyses were used to determine the direct and indirect effects of rainfall, food availability, growth and reproduction on the condition of each species. Monthly variation in condition and growth rate differed between species and sexes. Availability of fruit and arthropods explained a significant portion of the variance in growth rates of male N. squamipes and female O. russatus. Condition of females of these species was affected positively by food availability and negatively by reproduction and growth. Growth rate was correlated negatively with condition for males.