Extreme habitat specialization by the Amazonian dung beetle <i>Canthonidia rubromaculata</i>

Abstract Canthonidia rubromaculata is an Amazonian dung beetle with an extremely restricted distribution and low detectability, recorded only in Bolivia, Venezuela, Brazil and Peru. Available evidence indicates that it is a specialist of riverine beaches, open microhabitats characterized by high temperatures, intense solar radiation and limited scientific study, which are increasingly threatened by climate change and the expansion of artisanal gold mining. To evaluate its physiological vulnerability, we quantified the thermal limits of the species using respirometry with thermal ramps, generating continuous metabolic trajectories based on CO 2 production. We recorded a mean stress heat threshold (SHST) of 31.75°C (±3.39) and a critical thermal maximum (CTmax) of 45.46°C (±3.53), with consistent metabolic patterns among individuals and clear transitions between basal respiration, thermal stress and physiological failure. In parallel, we recorded microclimatic variation in beaches and forests using data loggers and documented surface activity, feeding behaviour and interspecific interactions with close‐focus cameras, providing previously unreported observations for this species. The proximity between the thermal limits of C. rubromaculata and the maximum temperatures recorded on beaches during the dry season suggests a reduced capacity to tolerate future thermal increases. Our study represents the first physiological characterization of this taxon and provides key evidence to assess its persistence under ongoing climate warming and the accelerated degradation of Amazonian riverine habitats.