Abstract
In their review, Bergerud et al. (Bergerud, A. T., Mossop, D. H., and Myrberget, S. 1985. Can. J. Zool. 63: 2240–2248) evaluated two hypotheses to explain changes between years in the number of breeding ptarmigan (Lagopus spp.): "(i) numbers are limited by territorial spacing behaviour (Watson and Moss 1972) [Watson, A., and Moss, R. 1972. Proc. Int. Ornithol. Congr. 15: 134–1491 and (ii) numbers change in response to annual variations in breeding success." Several of the general definitions or views that they proposed are theoretically unsound or ambiguous, and certain specific statements inaccurate. After stating that "the primary implication of the breeding success hypothesis, namely that chick survival to autumn will be reflected in the next year's population, is not a mutually exclusive test" and after giving no mutually exclusive test themselves, they went on to use the invalid test of a correlation between changes in numbers and breeding success as if it were mutually exclusive. The reviewers' conclusions are based largely on correlations of past measurements. Putting the two hypotheses to the test by experiments is likely to be a more reliable way forward.
Published Version
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