A Randomized Nearest-Neighbor Approach for Assessment of Character Displacement: the Vulture Guild as a Model

Abstract

Character displacement has been analysed in the past but not with an approach that considers nearest-neighbor distances between members of a guild. Vultures provide a model system in which to test a new analytical approach presented here to assess character displacement. Vultures are represented by two geographically isolated and taxonomically distinct groups: the Old World accipitrids and New World vultures. These two groups provide an excellent case of convergent evolution in which functional similarities can be compared among obligate carrion-feeding birds. The vulture guild was analysed from several geographic regions where species occur in a high diversity: East Africa, South Africa, the Indian subcontinent, Amazonia, and the pleistocene deposits from Rancho La Brea, California. A three-dimensional morphospace was constructed derived from features of the skull, beak, and mandible to assess feeding capabilities. Species packing and their distribution within the morphospace were compared using a nearest-neighbor approach through Monte Carlo simulations. Vultures seem to exhibit a similar array of ecomorphological types wherever they occur in a high diversity, even though there are phylogenetic differences among some regions. Phylogenetic effects appear to have little influence on the distribution of functional types in each region and evidence for character displacement was found only at Rancho La Brea where both Old and New World vultures were present.