Mudanças não-lineares na abundância de guildas tróficas e na composição de espécies de morcegos com a distância ao riacho determinam a largura da zona ripária para morcegos

Abstract

The width of riparian zones and its conservation has been topic of discussion in political and scientific circles. The Brazilian Forest Code (BFC), which regulates creation of Permanent Protection Areas (PPA) prescribes protection of riparian vegetation up to 30 m on both stream sides. Studies conducted in Central Amazon showed that this width is not efficient in maintaining plant and animal biodiversity and ecosystem processes associated to them. We investigated the influence of distance to the stream on bat guild and species abundance, number and composition. We hypothesize that bat assemblage changes with distance to the stream. We believe that this change occurs at species composition level with increasing abundance, mainly of frugivorous and nectarivorous bats in areas close to streams. Bats were captured with mist-nets in 24 riparian plots and 25 non-riparian plots within a trail grid in a primary terra-firme forest at northeast of Manaus, Amazonas State, Brazil. Each plot was sampled thrice in 7056 net-hours. A total of 1.138 bats were captured, composing 51 species, five families and five trophic guilds. We used model selection by AIC (Akaike Information Criterion) in linear and piecewise regressions to estimate existence of ecological threshold for bat assemblage. For animalivorous and nectarivorous bat abundance, quantitative and qualitative species composition and guild composition, piecewise models with one breakpoint were more parsimonious and had greater Akaike weights than linear models. Animalivorous bat abundance was higher close to the stream up to 181 m and frugivorous bat abundance decreased up to 50 m of distance to the stream. The change on animalivorous bat abundance suggests that feeding areas away from streams may provide enough food to maintain more individuals of that guild and the opposite of that may occur for frugivorous bat abundance. The width of riparian zone recognized by bat species was up to 114 m of distance to the stream and was given by qualitative composition model. Given this width, requirements of 30 m for forest protection in riparian PPAs with streams of up to 10 m do not incorporate composition of bat species in riparian areas. Clearing of vegetation after 30 m allowed by law reduces 380% of riparian forest habitat that is necessary for conservation of bat assemblage in riparian zones. Ecological thresholds obtained from studies in primary forests at community level, combined with landscape descriptors suitable to animal and plant species ecology should be an effective strategy to predict width of riparian habitats necessary for biodiversity preservation.