Edge effects on a litterfall frog community of "Estação Biológica de Boracéia"

Abstract

This project aims at determining the nature and extension of the edge effect upon richness, abundance and diversity of the litterfall community of anuran amphibians of "Estação Biológica de Boracéia" (EBB). Boracéia Biological Station is a conservation unity encompassing 16.450 ha, owned by the University of São Paulo (USP), and it is located in Serra do Mar, at 900 m above sea level within the Atlantic Rainforest domain, one of the wettest regions in Brazil. Thus, the litterfall frog community will be studied between May-2012 and April-2014, through establishing seven transects, each containing six 4x4m plots, disposed at edge distances 0, 25, 50, 100, 200 and 500 m, totaling 42 plots at BBS. Plots will be monitored during the wet and dry seasons. To characterize the environment inside the plots, the following variables will be measured: air temperature, relative air humidity, mean of the litterfall depth, cover percentage of the herb layer, canopy cover, circumference at breast height (CBH) of the trees e8cm CBH, and amount of fallen trees. Richness, dominance index and relative abundance of the species captured within the plots will be calculated. There will be created species accumulation curves after each field sampling, using the richness estimator that best fits. Species richness at different distances will be assessed through a regression analysis, considering the hypothesis that near the edge the species richness is reduced because of the habitat change caused by the proximity to an open area. The variation in species composition in relation to the edge distance will be analyzed according to the abundance calculus. Null models will also be used to find the probability of the distribution pattern to be random. The equitability in the species distribution in the edges will be calculated by Pielou index. The assessment of the environmental parameters influence on the community structure will be done through ordination analysis: i) to test the null hypothesis about absence of relation between environmental variables and the community composition, the group of variables will be represented by the orthogonal axis of the Principal Components Analysis (PCA), and the community structure will be represented by the orthogonal axis of Analysis of Non-Metric Multidimensional Scaling (NMDS), applied to the species abundance matrix, obtained through a similarity matrix calculated by the Bray-Curtis index. The influence of the group of environmental variables on the anuran community will be tested through simple regression analysis between the values of first the first dimension (axis) of NMDS and PCA; ii)the individual influence of each environmental variable upon the community structure will be assessed through Canonic Correspondence Analysis.