Within the semiarid Caatinga of Brazil, a biome dominated by a xeric arboreal-arbustive vegetation, many lizards are restricted to forest remnants associated with highlands. Although critical for conservation, data to understand the constraints on the distribution of those potential climate relicts are almost nonexistent. Here, we studied aspects of the ecology of the relict forest lizard Colobosauroides carvalhoi (Gymnophthalmidae) in the Caatinga of southern Piauí, northeastern Brazil. We combined data obtained through active sampling with voluntary thermal maximum (VTM) and measurements of environmental temperatures made in different habitats, microhabitats, and seasons to test the prediction that thermal constraints explain the local distribution and abundance of this species. In four field trips, we captured 22 individuals in pitfall traps and 93 in active searches, all in canyon-like valleys covered with semi-deciduous forests. Using plot sampling, we observed that density decreased as distance from rock cliffs increased. Density did not differ among sampling localities but varied among seasons. Field body temperatures were similar to soil temperatures under the leaf litter and lower than air and surface temperatures. Environmental temperatures in forests were lower than the VTM estimated for C. carvalhoi, especially under the leaf litter. Nevertheless, environmental temperatures usually exceeded the VTM at forest borders and in caatingas, in which the species was absent. Our results confirm that C. carvalhoi is spatially constrained to patches of semi-deciduous forests and suggest that its low thermal tolerance likely prevents it from occurring or dispersing through xeric habitats that predominates in Caatinga.
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