Diversidade beta no interflúvio Purus- Madeira : determinantes da estrutura das comunidades de Marantaceae, Araceae e Pteridófitas ao longo da BR 319, Amazonas, Brasil

Abstract

Knowledge of the distribution of species along environmental and spatial gradients is very important for the development of wise conservation policies. It is known that environmental heterogeneity is a key factor on the determination of a natural community's structure. Many studies suggest the existence of surrogate groups, i.e. groups that indicate more general patterns of distribution of species. But thi is still a controversial issue. To assess the variation in biological communities in the Purus-Madeira region, installed 36 plots of 500 m2, distributed in two study areas along BR-319 roadway (Manaus-Porto Velho). This study compared distribution patterns at meso and broad scales, for three groups of herbaceous plants (pteridophytes, Marantaceae and Araceae). Multivariate analysis were used to simplify species composition. Regression models were used to test how communities respond to environmental and geomorphological factors. The relative importance of geographical distance for differences in these communities was also assessed. The three communities responded differently to the gradients in litter and silt. Marantaceae them seems to be affected by understory cover. Results show that the environment, the geomorphology and the geographical distance affect the composition of Marantaceae and pteridophytes communities. Araceae communities were only affected by geographical distance. The proportion of each community affected by these factors was variable. For all three groups the differences of floristic composition were better explained by geographical distances than by environmental conditions. The results suggest that surrogate groups should be used carefully, since biological differences between groups lead to differencesin responses to the environment. Observations point to the sucessive presence and absence of different species along the highway. Therefore, small widely distributed areas would include more species. Nonetheless, it isn't possible to calculate the minimum area these protected sites should have, since there are no studies on how fragmentation and habitat loss affect Marantaceae, Araceae and pteridophytes in this area.