Diversidade, variação altitudinal e fatores ambientais que influenciam a distribuição da malacofauna terrestre em cinco localidades da Ilha Grande, Angra dos Reis, Rio de Janeiro, Brasil

Abstract

Terrestrial molluscs is one of the most threatened animal group in many parts of the world, mainly because their habitats are rapidly being reduced as a result of human occupation and exploration; however, in high richness regions as the Atlantic Rain Forest, it is unknown how many species actually exist nor how their communities are structured. The aim of this study was to verify: 1) whether there are differences in richness, abundance and composition of terrestrial molluscs, along the altitudinal gradient; 2) which environmental factors are associated with differences in the land snail fauna composition. Sampling occurred at Jararaca, Pico do Papagaio, Morro do Meio, Pedra d'Água and Parnaioca, all at Ilha Grande (23°05'- 23°15' S; 44°06'- 44°23' W), Rio de Janeiro, an important remnant of Atlantic Rain Forest. On each locality, seven plots were sampled at 100 m elevation intervals between 100 to 700 m. Each plot was sampled by time search for two hours and litter was collected down to the soil surface from ten quadrats of 25 × 75 cm where environmental variables were measure. For each locality, the richness and abundance data were used to calculate the dissimilarity index of Bray-Curtis, and with these data, we performed a cluster analysis to verify the existence of groups with biological identity. Using the groups formed in the biological cluster analysis, the collection areas were grouped to perform a discriminant analysis, using environmental data. A total of 2259 specimens, 41 species, 28 genera and 12 families were collected. Among the species collected, 17 species (41.5%) occurred in all the studied localities, seven (17.1%) species were collected in a single locality and five (12.2%) species were collected at two sites. Jararaca showed the greater abundance (526) whereas Pedra d'Água showed the lower abundance (306). Parnaioca and Morro do Meio showed the highest richness, corresponding to 30 species whereas Pedra d'Água showed the lowest richness, with 27 species. The micromolluscs corresponded to 20 species (48.8%) and 1694 specimens (75%). The family Scolodontidae and species Happiella sp. were dominant in all localities, occurring at all altitudes. The genera Prohappia Thiele, 1927 and Guestieria Crosse, 1872 and the species Happiella insularis (Boettger, 1889), Bulimulus transparens (Reeve, 1849), Drymaeus succineus Pilsbry (1901) and Pseudoxychona polytricha (Ihering, 1912) are cited for the first time for Ilha Grande. The distributions of relative abundances of species fitted the log-normal model. Regarding to richness along the altitudinal gradient, Morro do Meio and Pedra d'Água do not shown any pattern similar to those found in the literature, that is, richness peak at intermediate altitudes. Comparing discriminant analysis of all locations, the environmental factors associated to variation in species composition were atmospheric temperature, soil temperature, relative air humidity, luminosity and litter depth.