Estrutura da assembléia de pequenos mamíferos em um ambiente insular no Estado do Rio de Janeiro, Brasil

Abstract

Community assembly is the result of deterministic and stochastic processes that operate at different scales. On a local scale, factors such as structural diversity and habitat quality play a key role in determining the structure of communities. In this sense, riparian environments may be important in maintaining biodiversity. Riparian zones are transition interfaces between terrestrial and aquatic ecosystems and, therefore, are considered regions of high structural diversity and with a wide range of high-quality resources. Hence, the present study aimed to evaluate how small mammals are structured along an environmental gradient in the Ilha Grande State Park, as well as to evaluate differences in the structure of the small mammals assemblage in riparian and non-riparian environments. This study is part of the Atlantic Forest Biodiversity Program (PPBio) and uses the RAPELD sampling method (rapid assessment surveys at long term ecological research sites). For this purpose, assemblage of small mammals were sampled from October 2018 to October 2019 in 17 sites, eight riparian (RI) and nine non-riparian with uniform distribution (NR). Four capture sessions were carried out in each site in Ilha Grande, RJ. In each plot, 25 traps (12 Sherman and 13 Tomahawk) were installed every 10 meters, interspersed at ground level and in the understory. In total, 10 different species were registered, seven belonging to the Rodentia order and three species to the Didelphimorphia order. Among the rodents, the species with the highest number of records was Trinomys iheringi, followed by Euryoryzomys russatus and Nectomys squamipes. In the marsupial group, the most abundant species was Didelphis aurita. Only three species were recorded in the non-riparian sites: Oligoryzomys nigripes, Phyllomys pattoni and Rhipidomys itoan, and the number of captures for each species was only one individual. There were no differences in vegetation structure, composition and abundance of small mammals between riparian and non-riparian environments. Despite the homogeneity regarding the riparian and non-riparian environment observed for small mammals, the small mammals assemblage responded to the gradient of the vegetation structure. It was possible to observe that some species were restricted to one end of the gradient and others with a generalist behavior, occupying all or almost the entire gradient. Thus, the present study indicates that the presence of a watercourse is not the main factor structuring the small mammals assemblage on Ilha Grande, RJ, but the structure of vegetation. Therefore, water availability does not seem to be a limiting factor in a region such as the southwest coast of the state of Rio de Janeiro, where mean annual rainfall levels are high.