A Cold Truth: Bergmann’s Rule Holds for Warm-Blooded Animals but Not for the Cold-Blooded
A comprehensive study testing Bergmann’s rule—the hypothesis that animal body size increases with latitude—reveals a fundamental split based on thermoregulation. Analyzing species- and population-level data across amphibians, reptiles, birds, and mammals, researchers found strong support for the rule in endotherms (birds and mammals) but not in ectotherms (amphibians and reptiles). This pattern, driven by a negative correlation between body size and temperature in endotherms, underscores that Bergmann’s rule is not a universal ecological principle but a context-dependent pattern shaped by evolutionary history and ecological traits like thermoregulatory strategy, habitat, and geographic region.
Study Significance: This research provides critical empirical validation for a long-debated macroevolutionary pattern, directly informing models of adaptation and response to climate change. For professionals in evolutionary biology and ecology, it clarifies that predictive frameworks for species’ morphological responses to environmental gradients must be taxon-specific, integrating thermoregulation and life history. The findings highlight the differential sensitivity of endotherms and ectotherms to environmental shifts, a key consideration for conservation strategies and understanding future evolutionary trajectories under global warming.
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