Small mammal communities along the Brazilian Atlantic Forest: Local and regional drivers of composition and functional groups replacement

Background/Question/Methods

The Brazilian Atlantic Forest is a biodiversity hotspot that spans for 3000 km along the coast and comprises a mosaic of floristic formations. Small-mammal communities differ in diversity and composition, among sites, due to factors impacting at different temporal and spatial scales. The regional species pool consists mainly of three groups with different arrival dates in South America: marsupials (Didelphidae) at Cretaceous, Caviomorph rodents (Echimyidae) at Oligocene and native mice (Cricetidae, Sigmodontinae) at Pliocene. Environmental filtering, anthropogenic disturbances and subsequent secondary succession impact at local-ecological scales, leading to changes in small-mammal communities. This study aims to answer questions about the variation (at genus level) of small mammal communities along the Brazilian Atlantic Forest: 1) How do the composition of the communities vary among local habitats and regional floristic formations? 2) How are functional groups (higher taxa, locomotion modes, feeding guilds) represented among different local habitats and regional floristic formations? Our database consisted of relative abundance data of 38 genera in 88 sites sampled over 31 areas. We used species-centered Principal Components Analysis to summarize trends in the composition and diversity among sites in the Brazilian Atlantic Forest, as well as, to evaluate functional groups replacement along gradients.

Results/Conclusions

The main drivers of community composition were a) post clear-cut successional gradient and, b) altitudinal gradient. Three major community types were apparent: 1) late successional lowland/sub-montane forests dominated by a diverse set of marsupials; 2) early successional sites and natural open areas dominated by Sigmodontinae, (mainly Akodon and Oligoryzomys) and; 3) montane forests occupied by a diverse set of native rodents (with Oligoryzomys dominance). Another analysis restricted to the core habitats of the Atlantic Forest (mesic lowland/submontane sites) revealed that different environmental disturbances led to divergent faunal changes. These changes were due to the replacement of functional groups rather than simply due to the replacement of ecologically similar genera:  1) clear-cutting forests led to the replacement of a diverse set of Didelphidae by a few Sigmodontinae; 2) increased fragmentation led to the replacement of insectivore-omnivores by frugivore-granivores and frugivore-omnivores and;.3) burning, in contrast, favored insectivore-omnivores at the expense of frugivore-granivores. While regional and local drivers shape small-mammal communities, anthropogenic processes acting on local-ecological scale currently play a major role in differentiating small mammal communities along the Atlantic Forest at the taxonomical level studied.