The Grinnellian Niche of the Wood Thrush

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Abstract
Our results suggest that the limits of the breeding range of the wood thrush and its relative abundance within its range are not highly related to the presence of ecologically similar species. These parameters are better accounted for by variables such as species-specific nesting and foraging requirements, which in turn covary with the vegetation structure of the eastern deciduous forest. Studies of single-species geographical ecology should precede studies of assemblages. The Grinnellian model is more likely than the Hutchinsonian model to provide sound information on factors regulating the distribution and abundance of animals. Nevertheless, without controlled experiments both the Hutchinsonian and the Grinnellian models are descriptive, and inferences about processes underlying patterns will continue to be weak. The neo-Grinnellian approach uses some of the same analytical techniques as the Hutchinsonian approach, but it employs multiple comparisons to study the geographical ecology of single species, and it is cautious about interpretation. Comparisons with congeners and species of similar ecology are still of interest, including the extent to which species differences result from interspecific niche shifts. An important problem that will always plague niche analysis based an observational data is whether regional differences in resource use are a reflection of (1) biological differences among the populations; (2) measurement of resources that are irrelevant to the species; or (3) interspecific niche shifts. In cases in which controlled experiments are not possible, this problem can be addressed as single-species, large, multifactor studies in geographical ecology. These studies need not be cast in terms of community theory. Future studies should try to clarify the relationship between habitat selection and both Hutchinsonian and Grinnellian niche analysis. Careful design of sampling procedures with multiple comparisons could permit evaluation of the relative power of proposed mechanisms to explain observed patterns.