Morphological variation in the short-tailed fruit bat (Carollia) in Ecuador, with comments on the practical and philosophical aspects of boundaries among species.

The mechanisms for the morphological delimitation of species in Carollia remain poorly understood. This is the first study to assess variation in size and shape from strictly geometric terms. Both factors are assessed by statistical perspectives of distribution, overlap and relative distances. Despite its overlap, the size of the skull seems to be the most influential character for the discrimination of species, with shape playing a much smaller role. The smallest species seems to be the most distinct in shape, not only in terms of distance among centroids in morphometric space, but also in the overall trend and direction of variation. Contrary to previous studies, sexual dimorphism is not given by size but by distinct shapes of the skull. Characters such as the shape of the maxilla, previously described qualitatively as discrete with sharp boundaries, appear to be truly continuous with fuzzy borders among species. Because morphometric space is a gamut of continuous variation and overlap, the taxonomic error rate for size characters seems to be substantial for the medium-sized species (Carollia brevicauda Schinz, 1821), with approximately 30-40% of individuals erroneously assigned to a different species after a jackknifed discriminant function. This taxonomic error is higher for shape characters. Morphological, systematic and ecological consequences of the observed patterns of shape and size variation are commented within the context of previously proposed arguments and hypotheses.