Foster's rule

Foster's rule, also known as the island rule or the island effect, is an ecogeographical rule in evolutionary biology stating that members of a species get smaller or bigger depending on the resources available in the environment. For example, it is known that pygmy mammoths evolved from normal mammoths on small islands. Similar evolutionary paths have been observed in elephants, hippopotamuses, boas, sloths, deer (such as Key deer) and humans.^[1]^[2] It is part of the more general phenomenon of island syndrome which describes the differences in morphology, ecology, physiology and behaviour of insular species compared to their continental counterparts.

The rule was first formulated by van Valen in 1973^[3]^[4] based on the study by mammalogist J. Bristol Foster in 1964.^[5]^[6] In it, Foster compared 116 island species to their mainland varieties. Foster proposed that certain island creatures evolved larger body size (insular gigantism) while others became smaller (insular dwarfism). Foster proposed the simple explanation that smaller creatures get larger when predation pressure is relaxed because of the absence of some of the predators of the mainland, and larger creatures become smaller when food resources are limited because of land area constraints.^[7]

The idea was expanded upon in The Theory of Island Biogeography, by Robert MacArthur and Edward O. Wilson. In 1978, Ted J. Case published a longer paper on the topic in the journal Ecology.^[8]

Recent literature has also applied the island rule to plants.^[9]

There are some cases that do not neatly fit the rule; for example, artiodactyls have on several islands evolved into both dwarf and giant forms.^[10]^[11]

The Island Rule is a contested topic in evolutionary biology. Some argue that, since body size is a trait that is affected by multiple factors, and not just by organisms moving to an island, genetic variations across all populations could also cause the body mass differences between mainland and island populations.^[12]

References

^ Arsuaga, Juan Luis de; Klatt, Andy; Sastre, Juan Carlos (2002). The Neanderthal's necklace : in search of the first thinkers. New York : Four Walls Eight Windows. ISBN 978-1-56858-187-3.
^ Panafieu, Jean-Baptiste de; Gries, Patrick (2007). Evolution (1 ed.). New York: Seven Stories Press. ISBN 978-1-58322-784-8. OCLC 132681532.
^ Van Valen, L. (1973). "Body Size and Numbers of Plants and Animals". Evolution. 27 (1): 27–35. doi:10.2307/2407116. JSTOR 2407116. PMID 28563673.
^ Lokatis, S.; Jeschke, J.M. (2018). "The island rule: An assessment of biases and research trends". Journal of Biogeography. 45 (2): 289–303. Bibcode:2018JBiog..45..289L. doi:10.1111/jbi.13160.
^ Foster, J.B. (1964). "The evolution of mammals on islands". Nature. 202 (4929): 234–235. Bibcode:1964Natur.202..234F. doi:10.1038/202234a0. S2CID 7870628.
^ Foster, J. Bristol (2012). The evolution of the native land mammals of the Queen Charlotte Islands and the problem of insularity (Thesis). University of British Columbia. doi:10.14288/1.0107150.
^ Whittaker, R.J. (1998). Island biogeography: ecology, evolution, and conservation. Oxford University Press, UK. pp. 73–75. ISBN 978-0-19-850020-9.
^ Case, T.J. (1978). "A general explanation for insular body size trends in terrestrial vertebrates". Ecology. 59 (1): 1–18. Bibcode:1978Ecol...59....1C. doi:10.2307/1936628. JSTOR 1936628.
^ Biddick, M.; Hendriks, A.; Burns, K.C. (2019-08-19). "Plants obey (and disobey) the island rule". Proceedings of the National Academy of Sciences. 116 (36): 17632–34. Bibcode:2019PNAS..11617632B. doi:10.1073/pnas.1907424116. PMC 6731657. PMID 31427521.
^ Mazza, P.P.A.; Rossi, M.A.; Agostini, S. (2015). "Hoplitomerycidæ (Late Miocene, Italy), an Example of Giantism in Insular Ruminants". Journal of Mammalian Evolution. 22 (2): 271–77. doi:10.1007/s10914-014-9277-2. S2CID 16437411.
^ van der Geer, A.A.E. (2018). "Uniformity in variety: Antler morphology and evolution in a predator-free environment". Palaeontologia Electronica (21.1.9A): 1–31. doi:10.26879/834.
^ Lokatis, Sophie; Jeschke, Jonathan M. (2018). "The island rule: An assessment of biases and research trends". Journal of Biogeography. 45 (2): 289–303. Bibcode:2018JBiog..45..289L. doi:10.1111/jbi.13160.

External links

"Why Do Islands Breed Giants (And Sometimes Dwarfs)?", episode of PBS's Nova

[1] Arsuaga, Juan Luis de; Klatt, Andy; Sastre, Juan Carlos (2002). The Neanderthal's necklace : in search of the first thinkers. New York : Four Walls Eight Windows. ISBN 978-1-56858-187-3.

[2] Panafieu, Jean-Baptiste de; Gries, Patrick (2007). Evolution (1 ed.). New York: Seven Stories Press. ISBN 978-1-58322-784-8. OCLC 132681532.

[Valen1973-3] Van Valen, L. (1973). "Body Size and Numbers of Plants and Animals". Evolution. 27 (1): 27–35. doi:10.2307/2407116. JSTOR 2407116. PMID 28563673.

[Lokatis2018-4] Lokatis, S.; Jeschke, J.M. (2018). "The island rule: An assessment of biases and research trends". Journal of Biogeography. 45 (2): 289–303. Bibcode:2018JBiog..45..289L. doi:10.1111/jbi.13160.

[5] Foster, J.B. (1964). "The evolution of mammals on islands". Nature. 202 (4929): 234–235. Bibcode:1964Natur.202..234F. doi:10.1038/202234a0. S2CID 7870628.

[6] Foster, J. Bristol (2012). The evolution of the native land mammals of the Queen Charlotte Islands and the problem of insularity (Thesis). University of British Columbia. doi:10.14288/1.0107150.

[7] Whittaker, R.J. (1998). Island biogeography: ecology, evolution, and conservation. Oxford University Press, UK. pp. 73–75. ISBN 978-0-19-850020-9.

[8] Case, T.J. (1978). "A general explanation for insular body size trends in terrestrial vertebrates". Ecology. 59 (1): 1–18. Bibcode:1978Ecol...59....1C. doi:10.2307/1936628. JSTOR 1936628.

[9] Biddick, M.; Hendriks, A.; Burns, K.C. (2019-08-19). "Plants obey (and disobey) the island rule". Proceedings of the National Academy of Sciences. 116 (36): 17632–34. Bibcode:2019PNAS..11617632B. doi:10.1073/pnas.1907424116. PMC 6731657. PMID 31427521.

[Mazza2015-10] Mazza, P.P.A.; Rossi, M.A.; Agostini, S. (2015). "Hoplitomerycidæ (Late Miocene, Italy), an Example of Giantism in Insular Ruminants". Journal of Mammalian Evolution. 22 (2): 271–77. doi:10.1007/s10914-014-9277-2. S2CID 16437411.

[Geer2018-11] van der Geer, A.A.E. (2018). "Uniformity in variety: Antler morphology and evolution in a predator-free environment". Palaeontologia Electronica (21.1.9A): 1–31. doi:10.26879/834.

[12] Lokatis, Sophie; Jeschke, Jonathan M. (2018). "The island rule: An assessment of biases and research trends". Journal of Biogeography. 45 (2): 289–303. Bibcode:2018JBiog..45..289L. doi:10.1111/jbi.13160.

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v t e Biological rules
Rules	Allen's rule Shorter appendages in colder climates Bateson's rule Extra limbs mirror their neighbours Bergmann's rule Larger bodies in colder climates Cope's rule Bodies get larger over time Deep-sea gigantism Larger bodies in deep-sea animals Dollo's law Loss of complex traits is irreversible Eichler's rule Parasites co-vary with their hosts Emery's rule Insect social parasites are often in same genus as their hosts Fahrenholz's rule Host and parasite phylogenies become congruent Foster's rule (Insular gigantism, Insular dwarfism) Small species get larger, large species smaller, after colonizing islands Gause's law Complete competitors cannot coexist Gloger's rule Lighter coloration in colder, drier climates Haldane's rule Hybrid sexes that are absent, rare, or sterile, are heterogamic Harrison's rule Parasites co-vary in size with their hosts Hamilton's rule Genes increase in frequency when relatedness of recipient to actor times benefit to recipient exceeds reproductive cost to actor Kleiber's law An animals metabolic rate decreases with its size Hennig's progression rule In cladistics, the most primitive species are found in earliest, central, part of group's area Jarman–Bell principle The correlation between the size of an animal and its diet quality; larger animals can consume lower quality diet Jordan's rule Inverse relationship between water temperature and no. of fin rays, vertebrae Lack's principle Birds lay only as many eggs as they can provide food for Rapoport's rule Latitudinal range increases with latitude Rensch's rule Sexual size dimorphism increases with size when males are larger, decreases with size when females are larger Rosa's rule Groups evolve from character variation in primitive species to a fixed character state in advanced ones Schmalhausen's law A population at limit of tolerance in one aspect is vulnerable to small differences in any other aspect Thayer's law The top of an animals coloration is darker than the bottom Thorson's rule No. of eggs of benthic marine invertebrates decreases with latitude Van Valen's law Probability of extinction of a group is constant over time von Baer's laws Embryos start from a common form and develop into increasingly specialised forms Williston's law Parts in an organism become reduced in number and specialized in function
Related	Countergradient variation Where genetics opposes environment as a factor Gigantothermy Large ectothermic animals more easily maintain constant body temperature

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Decomposers	Chemoorganoheterotrophy Decomposition Detritivores Detritus
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Defense, counter	Animal coloration Anti-predator adaptations Camouflage Deimatic behaviour Herbivore adaptations to plant defense Mimicry Plant defense against herbivory Predator avoidance in schooling fish

v t e Ecology: Modelling ecosystems: Other components
Population ecology	Abundance Allee effect Consumer-resource model Depensation Ecological yield Effective population size Intraspecific competition Logistic function Malthusian growth model Maximum sustainable yield Overpopulation Overexploitation Population cycle Population dynamics Population modeling Population size Predator–prey (Lotka–Volterra) equations Recruitment Small population size Stability Resilience Resistance Random generalized Lotka–Volterra model
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Species interaction	Antibiosis Biological interaction Commensalism Community ecology Ecological facilitation Interspecific competition Mutualism Parasitism Storage effect Symbiosis
Spatial ecology	Biogeography Cross-boundary subsidy Ecocline Ecotone Ecotype Disturbance Edge effects Foster's rule Habitat fragmentation Ideal free distribution Intermediate disturbance hypothesis Insular biogeography Land change modeling Landscape ecology Landscape epidemiology Landscape limnology Metapopulation Patch dynamics r/K selection theory Resource selection function Source–sink dynamics
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