Phenotypic and Ecological Correlates of Population Decline in the World's Anurans

Anurans are profoundly affected by the ongoing biodiversity crisis. Understanding the drivers of their population decline is key to guiding management strategies and prioritize conservation efforts. Population trends have recently become a popular indicator of extinction risk, yet comprehensive global-scale assessments are still scarce, particularly those that account for phylogenetic nonindependence. In this study, we assess the ecological and environmental factors associated with population decline in the world's anurans. We conducted a phylogenetic generalized least squares analysis using large-scale datasets of population trend (as indicated by their IUCN status), morphology, geographical distribution, and climate variables across 5246 globally distributed species. Specifically, we tested whether body size (BS), range size, annual mean temperature (AMT), temperature annual range (TAR), climate moisture index (CMI), latitude, and environmental prevalence (i.e., relative availability of climate conditions in the geographical space) affect population trends. A large majority of evaluated species were in decline. Range size and TAR were negatively correlated with decline, whereas latitude was positively correlated. Climatic prevalence was not correlated with decline, although declining species often showed lower prevalence values. The findings underscore the critical state of anuran populations, which may worsen in the future due to synergistic effects with climate change. Therefore, we recommend initiatives, such as the establishment of protected areas with multiple narrowly-distributed species, and the increase of the population trend assessment coverage.