Temporal niche influences higher extinction risk among diurnal tetrapods from tropical regions

The extinction rates of Anthropocene biodiversity vary dramatically through geographic and phylogenetic space, with certain regions and lineages concentrating high defaunation rates, while others remain nearly unchanged. This heterogeneity results from (spatial and phylogenetic) variation in the interactions between species fitness-relevant traits and environmental threats that trigger the pathway to extinction. Existing evidence reveals that factors including life histories, ecophysiology, and resource-use generalism influence variation in species declines under rapidly changing environments. An emerging hypothesis predicts that species spread across different ‘locations’ of the 24h diel spectrum are exposed to different anthropogenic pressures on demographic stability (e.g. daytime contact with humans), which can trigger differential extinction risk among diurnal, nocturnal and cathemeral (day-night actives) species. However, this prediction remains largely neglected. Only a single large-scale test of this hypothesis, on mammals, exists, which documented higher declines in diurnal species, driven by primates. Here, we address this hypothesis across the world’s tetrapods, spanning >23,000 species across both endotherms and ectotherms for the first time. Our results reveal that extinction risk is higher across diurnal species from tropical regions with greater human footprint. Collectively, extinction risk is the synergistic outcome of the interplay between extrinsic human-induced pressures and species traits.