Density and Population Size of Mammals in Remnants of Brazilian Atlantic Forest.

Abstract

From October 1994 to April 1996, I surveyed six Atlantic forest reserves, two large (approximately 20,000 ha each), two medium-sized (approximately 2000 ha each), and two small (approximately 200 ha each), located in northern Espírito Santo, southeastern Brazil, for mammals openface> 1 kg body weight. My main objective was to assess the effects of fragmentation on population sizes and densities of five abundant species of forest-dwelling species (three primates and two rodents). I used line-transect sampling to survey mammals and estimated densities through the DISTANCE program. The average density of mammals increased from small to medium to large fragments, with small fragments having an average mammal density ( 7.6 individuals/km2 ) significantly lower than that of large fragments (20.9 individuals/km2 ). This trend was not significant when species that were extinct or absent in some fragments were excluded from the analysis. Shortage of food ( fruits) and predation by small cats ( Leopardus sp.) are the likely factors contributing to the demise of mammals, most of which are frugivores, in small fragments. Estimates of population sizes were on the order of several hundred to thousands of individuals for the large reserves, whereas comparable estimates for the other areas indicate a few hundred individuals for the medium-sized reserves and <100 individuals per species in the small reserves. The estimates provided here indicate that only Atlantic forest reserves of ≥20,000 ha can sustain viable populations ( Ne ≅ 500 individuals) of the five species studied, which represent only about 14% of all medium-sized to large species of mammals known to be present in fragments of this size. Given that only about 20% of all protected areas remaining in the Atlantic forest are equal to or larger than this size, management measures are badly needed to improve mammal conservation in this biome.