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The Adaptive Significance of Some Size Trends in Island Birds
P. R. Grant
Vol. 19, No. 3 (Sep., 1965), pp. 355-367
Published by: Society for the Study of Evolution
Stable URL: http://www.jstor.org/stable/2406446
Page Count: 13
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1. In North America and México there is a strong tendency for island birds to have a longer tarsus and bill than their mainland counterparts; but there is no such tendency for them to have a longer wing and tail. 2. Although climate and body-size are known to influence the size of tarsus and bill the larger dimensions on islands are considered to be adaptations primarily to ecological conditions. The bill is longer because it deals with a greater range of food-sizes, and the tarsus is longer because a greater variety of perches is used. 3. The differences in usage have arisen as a result of the absence, on the islands, of species with similar ecological requirements, which has permitted some of those present to extend their activities and occupy at least part of the vacant niches, sometimes in new habitats. 4. It is suggested that the same ecological conditions and responses have influenced the evolution of large body-size of island rodents in particular, and of mainland animals of several phyla in general.
Evolution © 1965 Society for the Study of Evolution