A insularização como agente de fragmentação florestal em comunidades de lagartos na Amazônia Central

Abstract

In a global context, there are few studies addressing effects on natural communities of habitat loss and isolation caused by hydroelectric dams. To better understand the impact of the flooding and island formation caused by the Balbina Reservoir on lizard communities of the central Amazon, I assessed the effects of island shape, size and isolation on species richness and composition and the influence of litter depth, and densities of trees and palms on the abundance of the most common species. Through litter browsing and visual encounter surveys, lizards were sampled on 20 islands and 6 control points on the nearby mainland. A total 1375 individuals were found, belonging to 16 taxa, in 5 families (Polychrotidae, Gekkonidae, Gymnophthalmidae, Scincidae and Teiidae). Islands taken as a group did not differ from the mainland in species richness. Considering only the island samples, the number of species was positively related to island area and negatively to isolation, but the relationship with isolation was leveraged by a single point. Path analysis indicated a direct effect of the landscape (area and isolation) on richness and weak direct effects of litter depth, of tree density and palm density. The species composition differed between islands and mainland when inferred from abundance data, but did not differ for presence/absence data. Using abundance data, three groups of species were found in a 2-dimensional PCoA ordination. Ordination scores of sites using all species were related to island area but not to isolation. However, when considering only species that occurred in more than 60% of plots, composition was related to isolation, but not to island area. This latter pattern was also found with presence/absence data using all species. A path analysis using quantitative and qualitative data indicated that the direct effect of island area on composition was greater than its total effect. The mediators of indirect effects - litter depth, tree density and palm density - all had negative effects. The same was not true for isolation; the total effect was greater than the direct effect because of the mediated positive contribution of litter depth. Environmental factors did not affect the abundance of Ameiva ameiva, Kentropyx calcarata and Plica umbra. Litter depth had a positive effect on Mabuya nigropunctata, and tree density on Gonatodes humeralis. The insularization caused by Balbina Reservoir has changed the structure of lizard communities. The area and isolation of each island influence composition.