Similaridade de espécies arbóreas em função da distância em uma floresta ombrófila na Floresta Nacional de Saracá-Taquera, Pará

Abstract

The distribution of species in tropical regions is very complex. Two principal models are commonly employed to explain species distributions: the Neutral Theory, and the Niche Theory. The former predicts that species coexistence is the result of a balance between immigration and extinction, while the Niche Theory predicts that natural resources are used differently among species. Studies carried out in tropical regions have demonstrated that species similarity decreases with geographical distance. However, few studies have been done comparing changes in species similarity with geographical distance on a local scale, where physical variables such as topography, altitude and soil type do not vary. The objective of this study is to test differences in species similarity with geographical distance from botanical plots on an Amazonian plateau in the Sacará-Taquera National Forest Reserve, in Pará, Brazil. 179 tree plots (10 x 250 m) were systematically distributed across the entire extent of the plateau, with a distance between plots varying between 200 meters and 9 km. A total of 631 species of tree were identified across all plots. The species area curve showed a clear tendency to asymptote. The estimated species richness (using first and second order Jackknife estimators) suggested 720 and 733 species respectively. The majority of species were present in low frequencies in the sampled plots, a pattern typical for the Amazon region. From the total of 631 species, 442 (70%) occurred in less than 10% of all parcels. There was a negative correlation between species similarity and plot distances. The lowest Sörensen similarity measures (ranging from 13% to 16%) were obtained from plots over 6 km apart, while the highest levels of similarity (ranging from 55% to 62%) were found comparing plots less than one kilometer apart. In conclusion, this study partially corroborates the Neutral Theory, where the similarity of species decreases with increasing geographical distances. However, the medium strength correlation between similarity and distance (r = -0.44) indicates that other factors are also important, and showing that the similarity of species in the tropical rain forests may be partly explained by other biotic and abiotic factors, as well as geographical distance.