Bergmann's rule#Hesse's rule

File:Bergmann's Rule.svg (Eurasian elk) in Sweden.{{Cite journal | doi=10.1007/BF00341355 | pmid=28306886 | title=Geographical and latitudinal variation in growth patterns and adult body size of Swedish moose (Alces alces) | journal=Oecologia | volume=102 | issue=4 | pages=433–442 | date=June 1995 | last1=Sand | first1=Håkan K. | last2=Cederlund | first2=Göran R. | last3=Danell | first3= Kjell |bibcode = 1995Oecol.102..433S | s2cid=5937734 }}]]

Human populations near the poles, including the Inuit, Aleut, and Sami people, are on average heavier than populations from mid-latitudes, consistent with Bergmann's rule.{{Cite journal | last1=Holliday | first1=Trenton W. | last2=Hilton | first2=Charles E. | doi=10.1002/ajpa.21226 | title=Body proportions of circumpolar peoples as evidenced from skeletal data: Ipiutak and Tigara (Point Hope) versus Kodiak Island Inuit | journal=American Journal of Physical Anthropology | volume=142| issue=2 | pages=287–302 | date=June 2010 | pmid=19927367}} They also tend to have shorter limbs and broader trunks, consistent with Allen's rule. According to Marshall T. Newman in 1953, Native American populations are generally consistent with Bergmann's rule although the cold climate and small body size combination of the Eastern Inuit, Canoe Nation, Yuki people, Andes natives and Harrison Lake Lillooet runs contrary to the expectations of Bergmann's rule. Newman contends that Bergmann's rule holds for the populations of Eurasia, but it does not hold for those of sub-Saharan Africa.{{cite journal |last=Newman |first=Marshall T. |date=August 1953 |title=The Application of Ecological Rules to the Racial Anthropology of the Aboriginal New World |journal=American Anthropologist |volume=55 |issue=3 |pages=311–327 |doi=10.1525/aa.1953.55.3.02a00020 |doi-access= }}

Human populations also show a decrease in stature with an increase in mean annual temperature.{{Cite journal |last=Roberts |first=DF |date=1954 |title=Body weight, race and climate |journal=American Journal of Physical Anthropology |volume=11 |issue=4 |pages=533–558 |doi=10.1002/ajpa.1330110404 |pmid=13124471 |url=https://scholar.google.com/scholar_lookup?journal=Am+J+Phys+Anthropol&title=Body+weight,+race,+and+climate&author=DF+Roberts&volume=4&publication_year=1953&pages=533-58&doi=10.1002/ajpa.1330110404& }} Bergmann's rule holds for Africans with the pygmy phenotype and other pygmy peoples. These populations show a shorter stature and smaller body size due to an adaptation to hotter and more humid environments.{{Cite journal |last1=Dominy |first1=Nathaniel |last2=Perry |first2=George |date=February 25, 2009 |title=Evolution of the human pygmy phenotype |journal=Trends in Ecology & Evolution |volume=24 |issue=4 |pages=218–225 |doi=10.1016/j.tree.2008.11.008 |pmid=19246118 |bibcode=2009TEcoE..24..218P |url=https://www.cell.com/trends/ecology-evolution/fulltext/S0169-5347(09)00042-1 }} With elevated environmental humidity, evaporative cooling (sweating) is a less effective way to dissipate body heat, but a higher surface area to volume ratio should provide a slight advantage through passive convective heat loss.

A 2019 study of changes in the morphology of migratory birds used bodies of birds which had collided with buildings in Chicago from 1978 to 2016. The length of birds' lower leg bones (an indicator of body size) shortened by an average of 2.4% and their wings lengthened by 1.3%. A similar study published in 2021 used measurements of 77 nonmigratory bird species captured live for banding in lowland Amazon rainforest. Between 1979 and 2019, all study species have gotten smaller on average, by up to 2% per decade. The morphological changes are regarded as resulting from global warming, and may demonstrate an example of evolutionary change following Bergmann's rule.{{Cite news|url=https://www.bbc.com/news/science-environment-50661448|title=Birds 'shrinking' as the climate warms|last=Vlamis|first=K.|date=4 December 2019|work=BBC News|access-date=5 December 2019|language=en-GB}}{{Cite web|url=https://www.audubon.org/news/north-american-birds-are-shrinking-likely-result-warming-climate|title=North American Birds Are Shrinking, Likely a Result of the Warming Climate|date=4 December 2019|website=Audubon | last = Liao | first = Kristine|language=en|access-date=5 December 2019}}{{Cite journal|last1=Weeks|first1=B. C.|last2=Willard|first2=D. E.|last3=Zimova|first3=M.|last4=Ellis|first4=A. A.|last5=Witynski|first5=M. L.|last6=Hennen|first6=M.|last7=Winger|first7=B. M.|date=2019|title=Shared morphological consequences of global warming in North American migratory birds|journal= Ecology Letters|volume= 23|issue= 2|pages=316–325|doi= 10.1111/ele.13434|pmid=31800170|hdl=2027.42/153188|s2cid=208620935|hdl-access=free}}{{Cite journal|last1=Jirinec|first1=Vitek|last2=Burner|first2=Ryan C.|last3=Amaral|first3=Bruna R.|last4=BierregaardJr|first4=Richard O.|last5=Fernández-Arellano|first5=Gilberto|last6=Hernández-Palma|first6=Angélica|last7=Johnson|first7=Erik I.|last8=Lovejoy|first8=Thomas E.|last9=Powell|first9=Luke L.|last10=Rutt|first10=Cameron L.|last11=Wolfe|first11=Jared D.|date=2021|title=Morphological consequences of climate change for resident birds in intact Amazonian rainforest|journal=Science Advances|volume=7|issue=46|pages=eabk1743|language=EN|doi=10.1126/sciadv.abk1743|pmc=8589309|pmid=34767440|bibcode=2021SciA....7.1743J }}

Bergmann's rule has been reported to be vaguely followed by female crocodilians.{{cite journal|last1= Lakin|first1= R.J.|last2= Barrett|first2= P.M.|last3= Stevenson|first3= C.|last4= Thomas|first4= R.J.|last5= Wills|first5= M.A.|title= First evidence for a latitudinal body mass effect in extant Crocodylia and the relationships of their reproductive characters|journal= Biological Journal of the Linnean Society|volume= 129|issue= 4|pages= 875–887|year= 2020|doi= 10.1093/biolinnean/blz208|doi-access= free}}{{cite web |url= https://www.newsweek.com/crocodilians-earth-100-million-years-survivors-mass-extinctions-climate-change-1492027|title= Crocodilians, Which Have Walked Earth for Nearly 100 Million Years, Are Survivors of Mass Extinctions and May Be Able to Adapt to Climate Change |last= Georgiou |first= A.|date= 12 March 2020|website= newsweek.com |publisher= Newsweek|access-date= 2020-03-13}} However, for turtles{{cite journal|last1= Angielczyk|first1= K.D.|last2= Burroughs|first2= R.W.|last3= Feldman|first3= C.R.|title= Do turtles follow the rules? Latitudinal gradients in species richness, body size, and geographic range area of the world's turtles|journal= Journal of Experimental Zoology Part B: Molecular and Developmental Evolution|volume= 324|issue= 3|year= 2015|pages= 270–294|doi= 10.1002/jez.b.22602|pmid= 25588662|doi-access= free|bibcode= 2015JEZB..324..270A}} or lizards{{cite journal |last1= Pincheira-Donoso|first1= D.|last2= Hodgson|first2= D.J.|last3= Tregenza|first3= T.|title= The evolution of body size under environmental gradients in ectotherms: why should Bergmann's rule apply to lizards?|journal= BMC Evolutionary Biology|volume= 8|issue= 68|date= 2008|page= 68|doi= 10.1186/1471-2148-8-68|pmid= 18304333|pmc= 2268677|doi-access= free|bibcode= 2008BMCEE...8...68P}} the rule's validity has not been supported.

Evidence of Bergmann's rule has been found in marine copepods.{{cite journal |author=Campbell, M.D. |display-authors=etal | title=Testing Bergmann's Rule in marine copepods |journal=Ecography |date=2021-08-21 |volume=44 |issue=9 |pages=1283–1295 |doi=10.1111/ecog.05545 |bibcode=2021Ecogr..44.1283C |url=https://doi.org/10.1111/ecog.05545|hdl=10072/407178 |s2cid=238701490 |hdl-access=free }}

Bergmann's rule cannot generally be applied to plants.{{Cite journal|last1= Moles|first1=A. T.|last2= Warton|first2=D. I.|last3= Warman|first3=L.|last4= Swenson|first4=N. G.|last5= Laffan|first5=S. W.|last6= Zanne|first6=A. E.|last7= Pitman|first7=A.|last8= Hemmings|first8=F. A.|last9= Leishman|first9=M. R.|date= 2009-09-01|title= Global patterns in plant height|journal= Journal of Ecology|volume= 97|issue= 5|pages= 923–932|doi= 10.1111/j.1365-2745.2009.01526.x|doi-access= free|bibcode=2009JEcol..97..923M }} Regarding Cactaceae, the case of the saguaro (Carnegiea gigantea), once described as "a botanical Bergmann trend",{{Cite journal |author1= Niering, W.A.|author2= Whittaker, R.H.|author3= Lowe, C.H.|year=1963 |title=The saguaro: a population in relation to environment |journal=Science |volume=142 |issue=3588|pages=15–23 |doi=10.1126/science.142.3588.15|pmid=17812501|bibcode = 1963Sci...142...15N }} has instead been shown to depend on rainfall, particularly winter precipitation, and not temperature.{{Cite journal|last= Drezner|first=T. D.|date= 2003-03-01|title= Revisiting Bergmann's rule for saguaros (Carnegiea gigantea (Engelm.) Britt. and Rose): stem diameter patterns over space|journal= Journal of Biogeography|volume= 30|issue= 3|pages= 353–359|doi= 10.1046/j.1365-2699.2003.00834.x|bibcode=2003JBiog..30..353D |s2cid=82276407 }} Members of the genus Rapicactus are larger in cooler environments, as their stem diameter increases with altitude and particularly with latitude. However, since Rapicactus grow in a distributional area in which average precipitation tends to diminish at higher latitudes, and their body size is not conditioned by climatic variables, this could suggest a possible Bergmann trend.{{Cite journal|last1= Donati|first1= D.|last2= Bianchi|first2= C.|last3= Pezzi|first3= G.|last4= Conte|first4= L.|last5= Hofer|first5= A.|last6= Chiarucci|first6= A.|date= 2016|title= Biogeography and ecology of the genus Turbinicarpus (Cactaceae): environmental controls of taxa richness and morphology|journal= Systematics and Biodiversity |volume= 15|issue=4 |pages=361–371 |doi= 10.1080/14772000.2016.1251504|s2cid= 90330480}}

File:Northern red fox & southern desert red fox.jpges from northern and southern populations]]

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 therefore stay warmer in cold climates. Warmer climates impose the opposite problem: body heat generated by metabolism needs to be dissipated quickly rather than stored within.{{cite journal |last1=Brown |first1=James H. |first2=Anthony K. |last2=Lee |title=Bergmann's Rule and Climatic Adaptation in Woodrats (Neotoma) |journal=Evolution |volume=23 |issue=2 |pages=329–338 |date=January 1969 |jstor=2406795 |doi=10.2307/2406795|pmid=28562890 }}

Thus, the higher surface area-to-volume ratio of smaller animals in hot and dry climates facilitates heat loss through the skin and helps cool the body. When analyzing Bergmann's Rule in the field, groups of populations being studied are of different thermal environments, and also have been separated long enough to genetically differentiate in response to these thermal conditions. The relationship between stature and mean annual temperature can be explained by modeling any shape that is increasing in any dimension. As you increase the height of a shape, its surface area-to-volume ratio will decrease. Modeling a person's trunk and limbs as cylinders shows a 17% decrease in surface area-to-volume ratio from a person who is five feet tall to a person who is six feet tall even at the same body mass index (BMI).

In marine crustaceans, it has been proposed that an increase in size with latitude is observed because decreasing temperature results in increased cell size and increased life span, both of which lead to an increase in maximum body size (continued growth throughout life is characteristic of crustaceans). The size trend has been observed in hyperiid and gammarid amphipods, copepods, stomatopods, mysids, and planktonic euphausiids, both in comparisons of related species as well as within widely distributed species. Deep-sea gigantism is observed in some of the same groups, possibly for the same reasons. An additional factor in aquatic species may be the greater dissolved oxygen concentration at lower temperature. This view is supported by the reduced size of crustaceans in high-altitude lakes.{{cite journal|last1= Peck|first1=L. S.|last2= Chapelle|first2= G.|title= Reduced oxygen at high altitude limits maximum size|journal= Proceedings of the Royal Society of London. Series B: Biological Sciences|volume= 270|issue= suppl. 2|pages=S166–S167|year= 2003|doi= 10.1098/rsbl.2003.0054|pmid=14667371|pmc=1809933}} A further possible influence on invertebrates is reduced predation pressure at high latitude.{{cite journal|author1-link=Elizabeth Harper (biologist)|last1= Harper|first1=E. M.|last2= Peck|first2=L. S.|title= Latitudinal and depth gradients in marine predation pressure|journal= Global Ecology and Biogeography|volume= 25|issue= 6|year= 2016|pages= 670–678|doi= 10.1111/geb.12444|doi-access= free|bibcode= 2016GloEB..25..670H}} A study of shallow water brachiopods found that predation was reduced in polar areas relative to temperate latitudes (the same trend was not found in deep water, where predation is also reduced, or in comparison of tropical and temperate brachiopods, perhaps because tropical brachiopods have evolved to smaller sizes to successfully evade predation).

In 1937 German zoologist and ecologist Richard Hesse 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.{{cite web| url=http://stommel.tamu.edu/~baum/paleo/paleogloss/node19.html#HessesRule| title=Hesse's rule| first=Steven| last=Baum| date=January 20, 1997| work=Glossary of Oceanography and the Related Geosciences with References| publisher=Texas Center for Climate Studies, Texas A&M University| access-date=2011-01-09| archive-url=https://web.archive.org/web/20101222133540/http://stommel.tamu.edu/~baum/paleo/paleogloss/node19.html#HessesRule| archive-date=December 22, 2010| url-status=dead}}

In a 1986 study, Valerius Geist claimed Bergmann's rule to be false: the correlation with temperature is spurious; instead, Geist found that body size is proportional to the duration of the annual productivity pulse, or food availability per animal during the growing season.{{Cite journal | doi=10.1139/z87-164| title=Bergmann's rule is invalid| journal=Canadian Journal of Zoology| volume=65| issue=4| pages=1035–1038| date=April 1987| last1=Geist | first1=Valerius | bibcode=1987CaJZ...65.1035G}}

Because many factors can affect body size, there are many critics of Bergmann's rule. Some{{Who|date=September 2019}} believe that latitude itself is a poor predictor of body mass. Examples of other selective factors that may contribute to body mass changes are the size of food items available, effects of body size on success as a predator, effects of body size on vulnerability to predation, and resource availability. For example, if an organism is adapted to tolerate cold temperatures, it may also tolerate periods of food shortage, due to correlation between cold temperature and food scarcity. A larger organism can rely on its greater fat stores to provide the energy needed for survival as well being able to procreate for longer periods.

Resource availability is a major constraint on the overall success of many organisms. Resource scarcity can limit the total number of organisms in a habitat, and over time can also cause organisms to adapt by becoming smaller in body size. Resource availability thus becomes a modifying restraint on Bergmann's Rule.{{Cite journal | doi=10.1111/j.1600-0706.2013.00463.x| title=Bergmann′s rule in mammals: A cross-species interspecific pattern| journal=Oikos |volume=122| issue=10| pages=1465–1472| date=October 2013 | last1=Clauss | first1=Marcus | last2=Dittmann | first2=Marei T. | last3=Müller | first3=Dennis W. H. | bibcode=2013Oikos.122.1465C| s2cid=44183222|display-authors=etal | url=http://www.zora.uzh.ch/id/eprint/81100/2/OIKOS_Bergmann_Suppl.pdf}}

Some examinations of the fossil record have found contradictions to the rule. For example, during the Pleistocene, hippopotamuses in Europe tended to get smaller during colder and drier intervals.{{Cite journal |last1=Mazza |first1=Paul P. A. |last2=Bertini |first2=Adele |date=24 October 2012 |title=Were P leistocene hippopotamuses exposed to climate-driven body size changes? |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1502-3885.2012.00285.x |journal=Boreas |language=en |volume=42 |issue=1 |pages=194–209 |doi=10.1111/j.1502-3885.2012.00285.x |s2cid=128992364 |issn=0300-9483 |access-date=20 January 2024 |via=Wiley Online Library}} Further, a 2024 study found the size of dinosaurs did not increase at northern Arctic latitudes, and that the rule was "only applicable to a subset of homeothermic animals" with regard to temperature when all other climatic variables are ignored.{{Cite web |last1=Grimes |first1=Marmian |last2=Fairbanks |first2=University of Alaska |title=Dinosaur study challenges Bergmann's rule |url=https://phys.org/news/2024-04-dinosaur-bergmann.html |access-date=2024-04-09 |website=phys.org |language=en}}

• Animal migration
• Biogeography
• Cold and heat adaptations in humans
• Gene flow
• Gigantothermy

{{Reflist|30em}}

• {{cite journal |last=Bergmann |first=Carl |title=Über die Verhältnisse der Wärmeökonomie der Thiere zu ihrer Grösse |journal=Göttinger Studien |year=1847 |volume=3 |issue=1 |pages=595–708 |url=https://books.google.com/books?id=EHo-AAAAcAAJ&pg=PA3}}
• {{cite journal |author=Roberts DF |year=1953 |title=Body weight, race and climate |journal=American Journal of Physical Anthropology |volume=11 |pages=533–558 |doi=10.1002/ajpa.1330110404 |pmid=13124471 |issue=4}}
• {{cite book |author=Roberts DF |year=1978 |title=Climate and Human Variability |edition=2nd |location=Menlo Park, CA |publisher=Cummings |url=https://books.google.com/books?id=umoSAQAAIAAJ|isbn=9780846566250 }}
• {{cite journal |author=Ruff CB |year=1994 |title=Morphological adaptation to climate in modern and fossil hominids |journal=Yearbook of Physical Anthropology |volume=37 |pages=65–107 |doi=10.1002/ajpa.1330370605|doi-access=free }}
• {{cite journal |author=Schreider E |year=1950 |title=Geographical distribution of the body-weight/body-surface ratio |journal=Nature |volume=165 |page=286 |doi=10.1038/165286b0 |pmid=15410342|bibcode=1950Natur.165..286S |issue=4190|doi-access=free }}

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Category:Animal size

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