Bergmann

Bergmann's Rule is an ecogeographical principle that was first proposed by the German biologist Carl Bergmann in 1847. It states that within a broadly distributed taxonomic clade, populations and species of larger size are found in colder environments, and species of smaller size are found in warmer regions. This rule applies to endotherms (warm-blooded animals) such as birds and mammals, but it has also been explored in relation to ectotherms (cold-blooded animals) though the patterns are less consistent.

Overview

The principle behind Bergmann's Rule is that larger animals have a smaller surface area relative to their volume. This means they have less skin relative to their mass through which to lose heat. Therefore, in colder climates, larger size is advantageous for conserving body heat. Conversely, in warmer climates, smaller bodies are advantageous because they have a larger surface area relative to their volume, allowing for more efficient heat dissipation.

Applications and Examples

Bergmann's Rule has been observed in numerous species across various regions. For instance, the polar bears of the Arctic are significantly larger than the brown bears found in warmer climates. Similarly, populations of deer, wolves, and even birds such as sparrows exhibit larger body sizes in colder regions compared to their counterparts in warmer areas.

Exceptions and Criticisms

While Bergmann's Rule provides a useful generalization, it is not without exceptions. Some species show the opposite pattern, or no clear pattern at all, which has led to criticism and calls for refinement of the rule. Factors such as resource availability, predation pressure, and life history traits can also influence body size, complicating the simple relationship between temperature and size.

Evolutionary Significance

Understanding the patterns described by Bergmann's Rule can offer insights into the evolutionary pressures faced by species in different environments. It also has implications for predicting how species might respond to climate change, as shifts in global temperatures could influence the distribution and body size of various animals.

See Also

• Allen's Rule
• Gloger's Rule
• Ecogeography