Environmental factors affecting the distribution of land snails in the Atlantic Rain Forest of Ilha Grande, Angra dos Reis, RJ, Brazil

Abstract

The distribution and abundance of terrestrial molluscs are affected by environmental factors, but data are lacking for Brazilian land snails. The aim of this study was to understand the relationship between measured environmental factors and the land-snail species composition of two hillsides covered with Atlantic Rain Forest on Ilha Grande. On each hillside, five plots located at 100 m intervals between 100 to 500 m asl were chosen. Each plot was sampled by carrying out timed searches and collecting and sorting litter samples from ten quadrats of 25 × 75 cm. A range of environmental data was measured for each of the quadrats in a plot. A Cluster Analysis was carried out for the richness and abundance data. The environmental variables were analysed using a Pearson Correlation Matrix and Discriminant Analysis. Our results show that the two mountains are similar in species richness, but species composition and abundance are different, probably reflecting observed differences in environmental conditions. The environmental factors associated with compositional variation between the two mountains were: atmospheric temperature, soil temperature, litter depth, and relative air humidity. Distinct luminosity and canopy closure conditions were related to the composition of the land-snail community of one hillside.Keywords: canopy closure, Gastropoda, litter depth, relative air humidity, temperature. Fatores ambientais afetando a distribuição de moluscos terrestres na Mata Atlântica da Ilha Grande, Angra dos Reis, RJ, Brasil ResumoA distribuição e a abundância de moluscos terrestres são afetadas por fatores ambientais, mas não existem dados para moluscos terrestres no Brasil. O objetivo deste trabalho foi entender a relação entre as variáveis ambientais aferidas e a composição da malacofauna terrestre em duas vertentes cobertas por Mata Atlântica, na Ilha Grande. Em cada vertente, foram escolhidos cinco plots, com intervalos de 100 m de altitude, de 100 a 500 m de altitude. Em cada plot, foram feitas a coleta direta e a coleta de serapilheira, utilizando 10 quadrats de 25 × 75 cm. Palavras-chave: fechamento do dossel, gastropoda, profundidade da serapilheira, temperatura, umidade relativa do ar.

Gradiente de altitude e riqueza de espécies: Como o estudo dos moluscos terrestres contribui com esta questão?

“…Ciente dessa problemática, o Laboratório de Malacologia Límnica e Terrestre da UERJ iniciou pesquisas sobre a diversidade de moluscos terrestres e gradiente de altitude na Ilha Grande, Rio de Janeiro. Uma parte desta pesquisa resultou em uma dissertação de mestrado (Nunes, 2007, Nunes & Santos 2010, 2012, outra parte integrará a Tese de Doutoramento da primeira autora. …”

Solaropsis brasiliana, anatomy, range extension and its phylogenetic position within Pleurodontidae (Mollusca, Gastropoda, Stylommatophora)

“…Live snails inhabit among leaf litter and below tree trunks laid on the floor were found in rainforest areas in the Tijuca area in Rio de Janeiro. In Ilha Grande specimens were found more frequently between 200 to 500 m asl, corresponding to the most preserved areas with higher humidity, canopy closure and litter depth associated to lesser luminosity and temperature (Nunes and Santos 2012).…”

“…Solaropsis brasiliana (Deshayes 1832) is a species emblematic to Rio de Janeiro State, often found in Ilha Grande (Haas 1953, Santos et al 2010, Nunes and Santos 2012. The taxonomic identification of material preserved in collections is often confused with Solaropsis pilsbryi Ihering 1900 and also with S. gibboni because of the lack of a clear diagnosis.…”

Population dynamics of Megalobulimus paranaguensis (Gastropoda: Pulmonata) in the southeast coast of Brazil

“…In the study of CHOI et al (2004), mathematical modeling using derived ordinary equations found that mortality in young Deroceras reticulatum (Muller, 1774) is more influenced by temperature, while recruitment rates in young individuals and the mortality rate of adults are more influenced by precipitation. Recent work by NUNES & SANTOS (2012) showed that the variables moisture, air temperature, soil temperature and depth of plant litter influence the distribution and abundance of terrestrial gastropods in the Atlantic Forest. Snails depend on high humidity to have an active life (BAKER 1958), being sensitive to desiccation, which tends to restrict their movements (GETZ 1974).…”