Bergmann's rule is an ecogeographic principle. It states that, within a widely distributed group of animals, the larger ones are found in colder environments, and the smaller ones are found in warmer regions.
So, for example, with bears the largest member is the polar bear, and the smallest members are found in subtropical areas (panda). The largest tiger is the Siberian tiger. Large mammals of the late ice age were in general larger than their descendants today.
The rule is named after nineteenth-century German biologist Carl Bergmann, who described the pattern in 1847, though he was not the first to notice it. Bergmann's rule appears to hold true for many mammals and birds, but there are exceptions.
Although originally put in terms of species, it seems to apply to populations within a species. Bergmann's rule is most often applied to mammals and birds which are endotherms, but some researchers have also found evidence for the rule in studies of ectothermic species.
In addition to being a general pattern across space, Bergmann’s rule has been reported in extinct populations from the fossil record. In particular, reversible dwarfing of mammals happened during two extremely warm but rather brief times in the Palaeogene.
Questions and Answers
Q: What is Bergmann's rule?
A: Bergmann's rule is an ecogeographic principle that states that animals within a widely distributed group tend to be larger in colder environments and smaller in warmer regions.
Q: Who discovered Bergmann's rule?
A: The rule is named after nineteenth-century German biologist Carl Bergmann, who described the pattern in 1847, although he was not the first to notice it.
Q: Does Bergmann's rule only apply to species or populations as well?
A: Although originally put in terms of species, Bergmann's rule seems to apply to populations within a species.
Q: Does Bergmann's rule apply only to mammals and birds?
A: Bergmann's rule is most often applied to mammals and birds which are endotherms but some researchers have also found evidence for the rule in studies of ectothermic species.
Q: Are there any exceptions to Bergmann's rule?
A: Yes, there are exceptions to Bergmann's rule, although it appears to hold true for many mammals and birds.
Q: Does Bergmann's rule only apply to living animals?
A: No, Bergmann's rule has been reported in extinct populations from the fossil record as well.
Q: Was there any dwarfing of mammals during extremely warm periods in the past?
A: Yes, reversible dwarfing of mammals happened during two extremely warm but brief times in the Palaeogene.
