Natural De Serpentes Em Uma Região No Sudoeste

Abstract

A snake richness of as much as 56 species was recorded at Espigao do Oeste (Rondonia). This makes the studied area faunistically similar to the Samuel Hydroelectric Plant (Rondonia), which is located close to it. The commonest snakes were Liophis reginae (18.6% of the total), Oxyrhopus melanogenys (8.4%), Chironius exoletus (6%), Boa constrictor (5.8%), Dipsas catesbyi (5.6%) and Drymarchon corais (5.6%). It is noticed a low frequency of Bothrops atrox (2%), the most abundant viperid in the Amazon. A lesser number of snakes was recorded during the driest months (from June to August), when there was a lesser occurrence of anuran amphibians as well. By seasonally observing the frequency of potential prey (anurans, lizards, marsupials and rodents), recorded by means of pitfall traps with drift fences (all groups) and time constrained search (lizards sleeping on the vegetation at night and calling anurans), it is noticed that there was availability of food supply throughout the year, although each group occurred at different abundance levels and peaks. Lizards (55.3% of the species), followed by anurans (48.2%), mammals (26.8%), birds (12.5%) and snakes (12.5%), are the main prey for the snakes in this community. A cluster analysis was carried out to produce a dendrogram with information on size (snout-vent length), feeding habits, period and forage substratum. Eight guilds of snakes were formed, according to the similarities in the use of resources. This cluster analysis grouped together species that, phylogenetically, were either close or distant, in order to mark the importance of historical and ecological factors to the structuring of this community. Most snake species were found throughout forested lands more than on pasture lands, showing that the weaker the vegetal structure, the lesser the number of species. Among the causes that may be enhancing or restraining the occurrence of certain species in this environment deforested for pasture, we have the rise in the predation rate, limitations in forage and thermoregulation activities and the decrease in some prey availability.