Lack's principle

Birds lay only as many eggs as they will be able to provide for.

If there are too many mouths to feed, fewer young will survive, reducing the parents' reproductive fitness.

Lack's principle, proposed by the British ornithologist David Lack in 1954, states that "the clutch size of each species of bird has been adapted by natural selection to correspond with the largest number of young for which the parents can, on average, provide enough food".^[1] As a biological rule, the principle can be formalised and generalised to apply to reproducing organisms in general, including animals and plants. Work based on Lack's principle by George C. Williams and others has led to an improved mathematical understanding of population biology.

Principle

Lack's principle implies that birds that happen to lay more eggs than the optimum will most likely have fewer fledglings (young that successfully fly from the nest) because the parent birds will be unable to collect enough food for them all.^[1] Evolutionary biologist George C. Williams notes that the argument applies also to organisms other than birds, both animals and plants, giving the example of the production of ovules by seed plants as an equivalent case. Williams formalised the argument to create a mathematical theory of evolutionary decision-making, based on the framework outlined in 1930 by R. A. Fisher, namely that the effort spent on reproduction must be worth the cost, compared to the long-term reproductive fitness of the individual.^[2] Williams noted that this would contribute to the discussion on whether (as Lack argued) an organism's reproductive processes are tuned to serve its own reproductive interest (natural selection), or as V.C. Wynne-Edwards proposed,^[3] to increase the chances of survival of the species to which the individual belonged (group selection). The zoologist J.L. Cloudsley-Thompson argued that a large bird would be able to produce more young than a small bird.^[4] Williams replied that this would be a bad reproductive strategy, as large birds have lower mortality and therefore a higher residual reproductive value over their whole lives (so taking a large short-term risk is unjustified).^[5] Williams' reply "is one of the most cited papers in life history evolution because it ... made it conceptually possible to find the optimal life history strategies in age-structured populations".^[6]

References

^ ^a ^b Lack, David (1954). The regulation of animal numbers. Clarendon Press.
^ Fisher, R. A. (1930). The genetical theory of natural selection. Oxford University Press.
^ Wynne-Edwards, V. C. (1962). Animal dispersion in relation to social behavior. Oliver and Boy.
^ Cloudsley-Thompson, J. L. (1955). Cragg, J. B.; Pirie, N. W. (eds.). The numbers of man and animals. Oliver and Boyd. pp. 54–55.
^ Williams, George C. (November 1966). "Natural Selection, the Costs of Reproduction, and a Refinement of Lack's Principle". The American Naturalist. 100 (916): 687–690. doi:10.1086/282461. JSTOR 2459305. S2CID 84993886.
^ Pasztor, E.; Loeschcke, V. (November 1989). "The Coherence of Cole's Result and Williams' Refinement of Lack's Principle". Oikos. 56 (3): 416–420. Bibcode:1989Oikos..56..416P. doi:10.2307/3565627. JSTOR 3565627.

[Lack1954-1] Lack, David (1954). The regulation of animal numbers. Clarendon Press.

[2] Fisher, R. A. (1930). The genetical theory of natural selection. Oxford University Press.

[3] Wynne-Edwards, V. C. (1962). Animal dispersion in relation to social behavior. Oliver and Boy.

[4] Cloudsley-Thompson, J. L. (1955). Cragg, J. B.; Pirie, N. W. (eds.). The numbers of man and animals. Oliver and Boyd. pp. 54–55.

[5] Williams, George C. (November 1966). "Natural Selection, the Costs of Reproduction, and a Refinement of Lack's Principle". The American Naturalist. 100 (916): 687–690. doi:10.1086/282461. JSTOR 2459305. S2CID 84993886.

[6] Pasztor, E.; Loeschcke, V. (November 1989). "The Coherence of Cole's Result and Williams' Refinement of Lack's Principle". Oikos. 56 (3): 416–420. Bibcode:1989Oikos..56..416P. doi:10.2307/3565627. JSTOR 3565627.

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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

Principle

See also

References