Metabolism constrains bird and mammal ranges and predicts shifts in response to climate change

AimWe test whether physiological constraints on maximum metabolic rate and the factor by which endotherms can elevate their metabolism (metabolic expansibility) govern cold range limits for mammal and bird species.\n\nLocationGlobal\n\nMethodsWe examine metabolic expansibility at the cold range boundary (MEO_SCPLOWCRBC_SCPLOW) and its trait predictors and then use MEO_SCPLOWCRBC_SCPLOW to project range shifts for 210 mammal and 61 bird species.\n\nResultsWe find evidence for metabolic constraints: the distributions of metabolic expansibility at the cold range boundary peak at similar values for birds (2.7) and mammals (3.2). The right skewed distributions suggest some species have adapted to elevate or evade metabolic constraints. Mammals exhibit greater skew than birds, consistent with their diverse thermoregulatory adaptations and behaviors. Mammal and bird species that are small and occupy low trophic levels exhibit high levels of MEO_SCPLOWCRBC_SCPLOW. Mammals with high MEO_SCPLOWCRBC_SCPLOW tend to hibernate or use torpor. Predicted metabolic rates at the cold range boundaries represent large energetic expenditures (>50% of maximum metabolic rates). We project species to shift their cold range boundaries poleward by an average of 3.9{degrees} latitude by 2070.\n\nMain conclusionsOur analysis suggests that metabolic constraints provide a viable mechanism for projecting cold range boundaries and range shifts in response to climate change for endotherms.