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Avian Relicts and Double Invasions in Peninsular India and Ceylon

S. Dillon Ripley
Evolution
Vol. 3, No. 2 (Jun., 1949), pp. 150-159
DOI: 10.2307/2405549
Stable URL: http://www.jstor.org/stable/2405549
Page Count: 10
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Avian Relicts and Double Invasions in Peninsular India and Ceylon
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Abstract

A discussion of the geological and physiographic factors influencing south India and Ceylon indicates that conditions there have been ideal for the development of ecological 'islands.' Given these islands and a succession of climatic epochs correlated with the glacial periods, numerous pluvial relicts have evolved. In addition, nine cases of presumed double invasions are known. These examples of double invasion have been divided into two types, depending on whether or not reproductive isolation has yet been established. Three of these cases, the owls, Glaucidium, the woodpeckers, Dinopium, and the racket-tailed drongos, Dissemurus, fall into the first category in which reproductive isolation is presumed or, in two cases, has been proved not to occur. These primarily allopatric forms are considered to be double invasions in view of their habitat preferences and of the development of highly distinctive external color differences. The remaining seven cases are primarily sympatric and may be classified as follows: (a) Partial range overlap with possible development of genetic and ecological differences; No. 7, Gracula species, and No. 8, Zosterops species. (b) Range overlap with the possibility of pre-adaptation as suggested by Lack, bearing in mind that the populations may be in flux at the present; No. 5, Megalaima species.2 (c) Range overlap with obvious structural difference and a possible threshold of habitat tolerance; No. 4, Centropus species. (d) Range overlap with insufficient explanation for the phenomenon of sympatric, closely related species being able to maintain themselves; No. 6, Turdoides species, and No. 3, Dicaeum species.

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