Diversidade da malacofauna terrestre em parcelas RAPELD no Parque Estadual da Ilha Grande, Angra dos Reis, Rio de Janeiro, Brasil

Abstract

Land snails are considered one of the most threatened groups, abundants at the Atlantic Forest, one of the biomes with the greatest diversity in the world; however, the scarcity of studies on the malacofauna call attention. The RAPELD methodology is very important for consolidation of long-term ecological research in Brazil, as a standard sample design allowing comparisons of different areas and research on the ecological processes that shape biodiversity. The objective of this study was to investigate the distribution of terrestrial molluscs present in permanent plots of RAPELD/ -East Module on Ilha Grande. Samples were collected in eight permanent plots located in the State Park of Ilha Grande. We established 10 collecting points each 25 meters in the plot and carried out direct collecting for 1 hour at each point, with a total of 10 hours of search. Litter samples were collected using quadrats of 25x75 cm, which was screened for the search of micro molluscs. We calculate the richness and abundance of species in each plot to assess community structure. For the diversity analysis we use the Simpson index, nonparametric estimators Jackknife, chao1 and curve of rarefaction To analyze the environmental factors that most influenced the composition and abundance of species and the separation of plots we used PCA and NMDS. We found373 specimens distributed in 42 species, 30 genera and 11 families. The plot with greater abundance was L2_3500 with 108 specimens (29%), followed by L1_3500 with 66 specimens (18%) and L1_4500 with 47 specimens (13%). The L1_2500 plot had the lowest abundance, with only nine specimens (2%). The plots studied showed that the largest and the smallest richness were L2_4500 and L1_2500 with 19 (45%) and six (14%) species, respectively. Scolodontidae was the richest family, corresponding to 28.5% of the sample, followed by Bulimulidae with 14.5% and, Charopidae and Subulinidae with 11%. Scolodontidae was also the most abundant family with 41% of specimens. Beckianum beckianum (Pfeifer, 1846) was the species with the greatest abundance, with 48 specimens (13%) distributed in only two plots: L1_4500 with nine specimens (19%) and L2_3500 with 39 specimens (36%). Five species were recorded for the first time to Ilha Grande Island. The PCA for the eight plots indicated that the variables soil temperatures and environmental temperature average, litter moisture and environmental moisture average contributed to the greater percentages in the two first axes, discriminating the plots according to habitat characterization. The plot L1_2500 showed a wide separation compared to the other plots. A simple regression between the single axis of NMDS and the second axis of the PCA was significant (r = 0.698; p = 0.05), indicating that molluscs communities are structured according to a humidity gradient. This work is pioneer in using the RAPELD methodology to study the distribution of terrestrial molluscs in Brazil and through integration with data from different areas, mainly botany and soil sciences, it will be possible to obtain new information on the distribution of malacofauna in the Atlantic Forest