Biology and Natural History of Brazilian Atlantic Forest Small Mammals

Abstract

During a 17-month study, 20 small mammal species were recorded in the forests of the western slopes of the Brazilian Atlantic coastal region in the state of Minas Gerais. A trapping effort of 57,120 trap nights resulted in 1366 captures of 692 individuals belonging to 8 marsupial and 12 rodent species. Both terrestrial and arboreal traps were used.

The common opossum Didelphis marsupialis was the most frequently trapped small mammal, followed by Marmosa incana. The spiny rat Proechimys setosus was the third most common small mammal and the most abundant rodent species. One marsupial and five rodent species were considered rare in this study, being represented in the sample by two or fewer individuals. Population turnover at the traplines was high for all species, with most individuals only appearing once in the total study sample.

Average body weight for the largest species, Didelphis marsupialis, was close to 1000 g, while for the smallest species, Oryzomys nigripes, it was approximately 20 g. Sexual dimorphism was common among marsupial species, but rare in rodents. Male marsupials, on average, tended to be larger than females. Male Oryzomys trinitatis, on the other hand, were slightly smaller than females.

Most marsupials are seasonal breeders, while rodents tend to reproduce throughout the year. The western slopes of the Atlantic forest are characterized by a pronounced dry season, and reproduction is concentrated in late dry and the early and midwet season. Seasonality of marsupial reproduction was recognized not only by the presence of breeding males and females, but also by juvenile recruitment into the population in subsequent months.

The vast majority of small mammal species have demonstrated a high degree of overlap in substrate use. A large number of small mammals have some level of scansorial ability, even the ones which are more frequently caught at the forest floor. It is also suspected that most species have mixed diets. Therefore, potential competition for resources is a definite possibility.