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Industrial Melanism in Biston betularia: The Rôle of Selective Predation

D. R. Lees and E. R. Creed
Journal of Animal Ecology
Vol. 44, No. 1 (Feb., 1975), pp. 67-83
DOI: 10.2307/3852
Stable URL: http://www.jstor.org/stable/3852
Page Count: 18
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Industrial Melanism in
                                Biston betularia: The Rôle of Selective Predation
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Abstract

(1) Dead individuals of typical, insularia and carbonaria morphs of the peppered moth, Biston betularia, were exposed on oak trees at Rubery, near Birmingham and at Starston and Hulver Street in East Anglia, all of which had until recently similar high melanic frequencies; the intensity of selective predation by birds was recorded. (2) The conspicuousness of these morphs to humans, their frequency in the wild and the reflectance of the trees were also recorded. (3) In East Anglia the trees have relatively high reflectance, and carbonaria is the most conspicuous morph as well as being subject to the most intense predation; typical is the least conspicuous and least preyed-upon form while insularia is intermediate in both respects. (4) At Rubery the trees are much darker than in East Anglia; here typical is the most conspicuous form and when the tree trunks are wet this morph is most heavily preyed upon. In some circumstances insularia appears to be better concealed than either of the other morphs. (5) Decreases in carbonaria frequency have occurred over the last twenty years both at our experimental sites and elsewhere north and east of a line from the Dee to the Thames. Conversely carbonaria has increased to the south and west of this line. (6) We dispute the view that high insularia frequencies are characteristic of areas with intermediate levels of pollution and that carbonaria replaces it in more polluted areas. Carbonaria is the commoner melanic form in rural East Anglia whereas insularia predominates in urban South Wales. (7) From rates of change in carbonaria frequency and from the discrepancy between the results of predation experiments and phenotype frequencies in the wild, non-visual selection against non-carbonaria has been calculated; assuming selection against carbonaria homozygotes to be 10%, these give values of up to 33%. (8) We consider that the polymorphism is maintained by heterozygous advantage independently of selection by predators. The extent of the advantage of heterozygotes may vary geographically.

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