Landsnail ecology

A recent paper by Nunes and Santos (2012) describes the different environmental factors affecting land snail populations on two hill sides at Ilha Grande, Brazil.

Schermafbeelding_2012-04-16_om

The abstract reads:

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. 

The series of sites were only separated by a relatively low hill crest (some 100s of meters). Remarkably the altitude of the sites within each series is of great influence. In the discriminant analysis, the sites at 200-400 m at the ‘oceanic hillside’ grouped together, while at the ‘continental hillside’ the plot of 200 m forms a group on its own, and the plots 300-500 m group together. The environmental factors that seem to be influential may be summarized as follows:

0schermafbeelding_2012-04-16_om

This is the first time that this kind of ecological study has been undertaken with Neotropical snail populations. It would be interesting to do a similar study in the Andes, where in some places there seems to be influence from the afternoon wind blowing upward to the seaward slopes.

Reference:
Nunes, G.K.M. & S.B. Santos (2012). Environmental factors affacting the distribution of land snails in the Atlantic Rain Forest of Ilha Grande, Angra dos Reis, RJ, Brazil. – Brazilian Journal of Biology 72: 79-86.
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