Is Bergmann's rule valid for terrestrial vertebrates?

Area of Science:

• Ecology
• Zoology
• Evolutionary Biology

Background:

• Bergmann's rule predicts larger body size in colder climates.
• Its applicability across vertebrate taxa and thermoregulatory strategies is debated.
• Previous studies show inconsistent support, particularly between endotherms and ectotherms.

Purpose of the Study:

• To test the consistency and strength of Bergmann's rule across major terrestrial vertebrate taxa.
• To investigate the influence of thermoregulatory strategy (endothermy vs. ectothermy) on Bergmann's rule.
• To assess Bergmann's rule at species and population levels.

Main Methods:

• Analysis of species- and population-level body size data for amphibians, reptiles, birds, and mammals.
• Correlation analysis between body size and latitude across taxa.
• Comparison of rule support between endotherms and ectotherms, and across different taxonomic levels (order/family, species, population).

Main Results:

• Bergmann's rule was supported in endotherms (birds, mammals) but not ectotherms (amphibians, reptiles).
• Support for the rule was stronger in endotherms (34%) than ectotherms (18%) at the order/family level.
• Body size correlated negatively with temperature in endotherms along latitudinal gradients, but not ectotherms.

Conclusions:

• Bergmann's rule is not a universal principle but a context-dependent pattern.
• Thermoregulatory strategy significantly moderates the rule's applicability.
• Ecological traits and phylogenetic history influence Bergmann's rule, highlighting differential sensitivity to environmental changes.