David Lack’s interest in coexisting avian seed eaters was extraordinarily seminal. His work, Darwin’s Finches (1947), suggested that several species of this family might be avoiding competitive exclusion by virtue of their dissimilar beak sizes. A likely hypothesis seemed to be that each beak size is specialised for a particular range of seed sizes (Bowman, 1961). Theories have since been developed that explain how this might come about (see, for example, MacArthur and Pianka, 1966; Emlen, 1966). In general they may be summarised by noting that they all require a trade-off in adaptiveness: the phenotype that is well adapted to utilising one portion of a resource spectrum is, perforce, poorly adapted for other portions of it. In the case of granivores, this might mean that, for a bird of given size, hulling over-large seeds is too costly in time or energy, and small seeds are too unrewarding, to be profitable. MacArthur and MacArthur (1972) have shown that this is probably true for certain American birds.
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- Bowman, R. I. (1961). Morphological differentiation and adaptation in the Galapagos finches. Univ. Cal. Publ. Zool., 58, 1–302.Google Scholar
- Brown, J. H. (1975). Geographical ecology of desert rodents, in “Ecology and Evolution of Communities” (eds. M. L. Cody and J. M. Diamond.) Harvard University Press, Cambridge, Massachusetts, 315–341.Google Scholar
- Dunham, M. (1968). A comparative food habit study of two species of kangaroo rats, Dipodomys ordii and Dipodomys merriami. M.S. thesis, University of New Mexico, Albuquerque. 25 pp.Google Scholar
- Franz, C. E., Reichman, O. J. and Van de Graeff, K. M. (1973). Diet, food preferences and reproductive cycles of some desert rodents. Research Memorandum, RM 73–74.Google Scholar
- Lack, D. L. (1947). Darwin’s Finches. Cambridge University Press, London.Google Scholar
- Levins, R. (1968). Evolution in Changing Environments, Princeton University Press, Princeton, New Jersey.Google Scholar
- Rosenzweig, M. L. (1974). On the evolution of habitat selection. In Proc. 1st Int. Congr. Ecology, 401–404.Google Scholar