The impact of individual tree harvesting on thermal environments of lizards in Amazonian rain forest

Single-tree harvesting with on-site lumber production produces gas in Amazonian forest canopy that are structurally different from natural treefall gaps. Harvest gaps are much more open, and there is neither leaf litter nor partial shading as in natural treefalls, so these anthropogenic gaps receive more intensive sunlight. We used HOBO XT temperature and light data loggers to measure thermal environments in forest patches. These data were combined with data on lizard activity,activity temperatures, and habitat use to determine whether human-made gaps influence the structure of Amazon forest lizard assemblages. Human-made treefalls are not only more extreme thermally than surrounding forest habitat patches and natural treefalls,but they are warmer than expected based on increased light alone. Large-bodied teiid lizards,which are typically uncommon or rare within forest, bask in sun in treefalls to gain heat. The body temperatures of these heliotherms average 36.1 degrees C. Nonheliothermic species avoid treefalls and remain in the shade within the forest. Their body temperatures average 27.7 degrees C. Heliothermic lizards using treefall gaps are large-bodied predaceous species that feed on vertebrates as well as invertebrates. Increasing the number of anthropogenic treefall gaps in a forest may increase the immigration and population growth of heliothermic lizards, thereby increasing their population density. Predation by these lizards and dominance over smaller lizards in interference competition (for food) may have a cascading effect on forest species, changing community structure.