Absence of edge effect on small mammals in woodland-savannah remnants in Brazil

Abstract

We evaluated the effect of edge on the richness, species composition, diversity, and abundance of small-mammal assemblages in remnants of woodland savannah in the Cerrado biome, south-western Brazil. Four remnants were sampled from September 2003 to July 2004, each one sampled in two field phases of 10 consecutive nights. Four sampling areas were selected in each remnant, two in edges and two in interiors (at least 200 m distant from the abrupt edge); each different habitat received a grid of 45 live-traps or a transect line pitfall-traps with 10 capture buckets. Structural variables of the vegetation at the edges and interiors were also measured in these habitats by two sampling methods. The gradients of fauna and vegetation were analysed in the edge-interior gradient (10 to 90 m inside the remnant). The trapping effort resulted in 342 captures of 219 individuals of 12 species. There was no evidence of edge effect on the small-mammal assemblages for richness, species composition, diversity and species abundance, but there was an apparent edge-interior gradient in the vegetation (e.g., understorey plants and bamboos). Results are discussed in the light of a supposed plasticity to environmental change faced by the small mammals from the Cerrado biome combined to a relatively good conservation of edges, since the structural parameters were rather similar between edges and interiors, despite the observed gradient up to 90 m within the remnants. Fences protecting edges from cattle and absence of water for cattle consuming in remnants were thought to be the main reasons for the observed edge conservation.