Mammal niches are not conserved over continental scales

The niche conservatism hypothesis states that a species’ relationships to habitat and climate conditions are maintained across space and time ^1–6 . Niche stationarity is assumed when ecologists estimate species’ habitat needs or transfer findings across geographic regions ^7,8 . Recent studies show that some species’ associations with climate and habitat vary spatially, contradicting the niche conservatism hypothesis ^9–18 . The sources of this nonstationarity are unknown and potential mechanisms remain untested. Here we show that the environmental niches of 36 common North American mammals vary spatially across dimensions of human influence, climate, and landscape. Spatial variation is not explained by known genetic subspecies lineages. Instead, niches vary at a relatively fine spatial scale consistent with adaptations by animals to local conditions, which may be explained by genetic or behavioral changes or by unmodeled interactions with unobserved variables. Spatially varying ecology means that static niche models are not appropriate at large scales and extrapolating species’ niches to novel contexts may be impossible ¹⁹ . This complicates management decisions based on transferring findings across space and projecting species’ current environmental associations to responses to future change, but may provide optimism if nonstationarity represents potential for rapid evolutionary rescue.