Pattern, process and the evolution of the African antelope (mammalia: bovidae)
The methods of vicariance biogeography are in general rendered equivocal by widespread taxa. Standard methods resort to ad hoc assumptions in their treatment of widespread cases, and the results are always si bordinate to the addition of new data on endemic sister taxa. I introduce an alternative method for the analysis of widespread taxa based on the vicariance model. The method requires first the development of a habitat model for each species included in the analysis. I analyse the actual and "potential" distributions by cladistic methods, employing a weighting system designed to factor out the influence of ecological similarity. The resolution of the inferred area relationships is seen to increases with the application of the weighting-compelling evidence that the pattern reflects historical relationship. I review current approaches to the modelling of habitats. All seem to be based on an ecological model of equilibrium, where the limits of actual species distributions are thought to reflect habitat, as if historical contingency played no significant part in determining the shape of real distributions. Under this model all approaches are group discrimination methods. I reject these methods and develop a new method based on principal component analysis. I analyse the distributions of all extant endemic African antelope and derive probability surfaces for each species. The model output can be interpreted as species distribution free oflHstory-its potential distribution. This is different from assuming that actual distributions are free of history. Areas oferdemism are seen to be historical entities, not simply distributional ones, and the resulting area cladograrn is interpreted as the hierarchical pattern of endemism. A striking feature of the inferred pattern of endemism is the intersection of an east-west equatorial biota, and a north-south savanna biota. These bisect in East Africa at the centre of highest antelope diversity. I predict that this feature will be seen to be the most persistent feature of endemic structuring in other African taxa with high East African diversity.
A Thesis Submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in Fulfillment of the Requirements for the Degree of Doctor of Philosophy. October, 1995.
African antelope, Biota, Taxa