HOMOPLASY AS PATTERN: MULTIVARIATE ANALYSIS OF MORPHOLOGICAL CONVERGENCE IN ANSERIFORMES

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Abstract
Abstract— A multivariatc model for taxa and characters is presented that represents taxa as points in an ordination space such that shared derived character states define groups of taxa or regions in this space. This model is compared, in terms of concepts of information content and explanatory power, to the eladistie model that relates characters and taxa to a hierarchical pattern. While a cladogram may be identified with a phylogenetic hypothesis, the ordination pattern may be equated with hypotheses about similarities among the taxa in habitat, feeding mode, or other ecological factors.This basic data‐pattern model is appropriate for the explanation of the character convergences implied by a particular phylogenetic hypothesis. Under the assumptions of the model, the underlying ordination pattern may be inferred from the observed character data using robust ordination procedures recently developed in community ecology.As an illustration of the method, the morphological convergences derived from a recent phylogenetic hypothesis for genera of Anseriformes are analysed. In the resulting two‐dimensional ordination, the genera are arranged such that the convergenlly derived states form regions in the space. While this pattern implies that some of the taxa that are close together in the space are phylogcnetically dissimilar, taxa that are close together in the space are found to be similar in their mode of feeding. Thus, the ordination demonstrates that taxa sharing these morphological convergences tend to utilize habitat in the same way in terms of mode of feeding.The explanatory power of the pattern and the degree of recovery of habitat information are tested against null hypotheses using Monte Carlo simulations.Extensions of the method are discussed, including applications to studies of parasite—host relationships and to biogeography.