The use of subspecies in the systematics of southern African white-eyes: historical entities or eco-geographic variants

The recognition of objectively diagnosable and evolutionarily significant terminal taxa, that is, evolutionarily significant units (ESU), is essential for the generation of defensible taxic hypotheses necessary for all forms of evolutionary and comparative biology and for effective guiding of biodiversity conservation. However, there has been a long and on-going, sometimes heated debate, on the merits of the subspecies category in this endeavour. To determine possible ESU present in southern African white-eyes, Zosterops spp., we used uni- and multivariate statistical approches to re-investigate the morphological characteristics (morphometric and plumage coloration) used in past taxonomic studies to propose nine putative southern African Zosterops ESU, described at the time as subspecies. Four ESU emerged from these analyses. Geographical, discriminatory, multifaceted analyses suggest that these four taxa, Z. senegalensis, Z. virens, Z. capensis and Z. pallidus warrant species status.