Bergmann's Rule
Encyclopedia
Bergmann's rule is an ecogeographic
principle that states that within a broadly distributed genus, species of larger size are found in colder environments, and species of smaller size are found in warmer regions. Although originally formulated in terms of species within a genus, it has often been recast in terms of populations within a species. It is also often cast in terms of latitude. The rule is named after a nineteenth-century German
biologist, Christian Bergmann
, who was among the first to describe the pattern in 1847 (but see ). Bergmann's rule is most often applied to mammals and birds which are endotherm
s, but some researchers have also found evidence for the rule in studies of ectothermic species. While Bergmann's rule appears to hold true for most mammals and birds, there are exceptions.
There seems to be a tendency for larger-bodied animals to conform more closely than smaller-bodied animals, at least up to certain latitudes, perhaps reflecting a reduced ability to avoid stressful environments by burrowing or other means. In addition to being a general pattern across space, Bergmann’s rule has been reported in populations over historical and evolutionary time when exposed to varying thermal regimes. Note that Bergmann's rule describes a tendency of body mass variation within groups; it does not suggest that large-bodied animals do not occur in warm climates.
, Aleut, and Sami
people, are on average heavier than populations from mid-latitudes, consistent with Bergmann's rule. They also tend to have shorter limbs and broader trunks, consistent with Allen's rule
. According to Marshall T. Newman in a 1953 article for the Journal of the American Anthropologist, Native American populations are generally consistent with Bergmann's rule although the cold climate and small body size combination of the Eastern Eskimo, Canoe Indians, Yuki, Andes natives and Harrison Lake Lillouet runs contrary to the expectations of Bergmann's rule. Newmann contends that Bergmann's rule holds for the populations of Eurasia, but it does not hold for those of sub-Saharan Africa.
s. On the other hand, warmer climates impose the opposite problem: body heat generated by metabolism needs to be dissipated quickly rather than stored within. Thus, the higher surface area-to-volume ratio of smaller animals in hot and dry climates facilitates heat loss through the skin and helps cooling of the body.
proposed an extension of Bergmann's rule. Hesse's rule, also known as the heart–weight rule, states that species inhabiting colder climates have a larger heart in relation to body weight than closely related species inhabiting warmer climates.
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...
principle that states that within a broadly distributed genus, species of larger size are found in colder environments, and species of smaller size are found in warmer regions. Although originally formulated in terms of species within a genus, it has often been recast in terms of populations within a species. It is also often cast in terms of latitude. The rule is named after a nineteenth-century German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
biologist, Christian Bergmann
Christian Bergmann
Karl Georg Lucas Christian Bergmann was a German anatomist, physiologist and biologist who developed the Bergmann's rule.- Biography :...
, who was among the first to describe the pattern in 1847 (but see ). Bergmann's rule is most often applied to mammals and birds which are endotherm
Endotherm
An endotherm is an organism that produces heat through internal means, such as muscle shivering or increasing its metabolism...
s, but some researchers have also found evidence for the rule in studies of ectothermic species. While Bergmann's rule appears to hold true for most mammals and birds, there are exceptions.
There seems to be a tendency for larger-bodied animals to conform more closely than smaller-bodied animals, at least up to certain latitudes, perhaps reflecting a reduced ability to avoid stressful environments by burrowing or other means. In addition to being a general pattern across space, Bergmann’s rule has been reported in populations over historical and evolutionary time when exposed to varying thermal regimes. Note that Bergmann's rule describes a tendency of body mass variation within groups; it does not suggest that large-bodied animals do not occur in warm climates.
Humans
Human populations who live near the poles, including the InuitInuit
The Inuit are a group of culturally similar indigenous peoples inhabiting the Arctic regions of Canada , Denmark , Russia and the United States . Inuit means “the people” in the Inuktitut language...
, Aleut, and Sami
Sami people
The Sami people, also spelled Sámi, or Saami, are the arctic indigenous people inhabiting Sápmi, which today encompasses parts of far northern Sweden, Norway, Finland, the Kola Peninsula of Russia, and the border area between south and middle Sweden and Norway. The Sámi are Europe’s northernmost...
people, are on average heavier than populations from mid-latitudes, consistent with Bergmann's rule. They also tend to have shorter limbs and broader trunks, consistent with Allen's rule
Allen's rule
Allen's rule is a biological rule posited by Joel Asaph Allen in 1877. It states that endotherms from colder climates usually have shorter limbs than the equivalent animals from warmer climates.- Theory :...
. According to Marshall T. Newman in a 1953 article for the Journal of the American Anthropologist, Native American populations are generally consistent with Bergmann's rule although the cold climate and small body size combination of the Eastern Eskimo, Canoe Indians, Yuki, Andes natives and Harrison Lake Lillouet runs contrary to the expectations of Bergmann's rule. Newmann contends that Bergmann's rule holds for the populations of Eurasia, but it does not hold for those of sub-Saharan Africa.
Explanations
The earliest explanation, given by Bergmann when originally formulating the rule, is that larger animals have a lower surface area to volume ratio than smaller animals, so they radiate less body heat per unit of mass, and stay warmer in cold climateClimate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
s. On the other hand, warmer climates impose the opposite problem: body heat generated by metabolism needs to be dissipated quickly rather than stored within. Thus, the higher surface area-to-volume ratio of smaller animals in hot and dry climates facilitates heat loss through the skin and helps cooling of the body.
Hesse's rule
In 1937 German zoologist and ecologist Richard HesseRichard Hesse
Richard Hesse was a German zoologist and ecologist.Hesse took his PhD in 1892 from the University of Tübingen and was subsequently appointed lecturer, later extraordinary professor of zoology at the same university...
proposed an extension of Bergmann's rule. Hesse's rule, also known as the heart–weight rule, states that species inhabiting colder climates have a larger heart in relation to body weight than closely related species inhabiting warmer climates.
See also
- GigantothermyGigantothermyGigantothermy is a phenomenon with significance in biology and paleontology, whereby large, bulky ectothermic animals are more easily able to maintain a constant, relatively high body temperature than smaller animals by virtue of their smaller surface area to volume ratio...
– large ectothermic animals more easily maintain constant body temperature - Insular dwarfismInsular dwarfismInsular dwarfism, a form of phyletic dwarfism, is the process and condition of the reduction in size of large animals – typically mammals – when their population's range is limited to a small environment, primarily islands. This natural process is distinct from the intentional creation of dwarf...
– small populations promote reduction in size of individuals - Allen's RuleAllen's ruleAllen's rule is a biological rule posited by Joel Asaph Allen in 1877. It states that endotherms from colder climates usually have shorter limbs than the equivalent animals from warmer climates.- Theory :...
– populations have shorter appendages in colder climates - Animal migrationAnimal migrationAnimal migration is the relatively long-distance movement of individuals, usually on a seasonal basis. It is a ubiquitous phenomenon, found in all major animal groups, including birds, mammals, fish, reptiles, amphibians, insects, and crustaceans. The trigger for the migration may be local...
- Gene flowGene flowIn population genetics, gene flow is the transfer of alleles of genes from one population to another.Migration into or out of a population may be responsible for a marked change in allele frequencies...