Tree cavities as keystone structures in a semiarid region: Interspecific aggregations of anurans in the Brazilian Caatinga

Abstract

Tree cavities function as key microclimatic refuges for anurans in the semiarid Caatinga biome of northeastern Brazil, where we document previously unreported interspecific aggregations during the dry season. Observations from fauna rescue operations preceding vegetation clearance revealed eight distinct aggregations within cavities of two native tree species, Commiphora leptophloeos and Amburana cearensis. Aggregations consisted of 6–98 adult individuals (total = 475), with up to six co-occurring species belonging to three families. Paired microclimatic measurements from 32 cavities showed that these structures buffered extreme external conditions, maintaining internal temperatures 5.43°C lower and relative humidity 15.0% higher than surrounding environments. Thermal buffering increased significantly with cavity depth and entrance diameter (p < 0.001), highlighting the role of cavity morphology in determining refuge quality. Our findings establish tree cavities as keystone structures for amphibian assemblages in the Caatinga and reveal an overlooked ecological role of cavity-bearing trees in seasonally dry tropical ecosystems. Given ongoing habitat conversion and projected increases in aridity, incorporating tree cavity conservation into environmental licensing and land management practices may be critical for maintaining amphibian diversity in this threatened biome.