WHAT TO PROTECT - SYSTEMATICS AND THE AGONY OF CHOICE

Politicians and scientists alike now agree that a priority list of global centres for preservation of biological diversity is required. Diversity has generally been measured only in terms of species richness, or in the form of indices combining richness with abundance. Such measures are considered inadequate for the task in hand. A novel index, based on the information content of cladistic classifications and giving a measure of taxonomic distinctness, is introduced. This taxic diversity measure, when coupled with detailed knowledge of distribution, can be used in modified analyses of the type previously developed as 'critical faunas analysis' or 'network analysis'. Central to all such analyses is the concept of complementarity of floras or faunas. By employing complementarity, step-wise procedures can identify optimally efficient, single-site sequences of priority areas for a group, taking existing reserves into account or not, as required. For practical planning it is concluded that two basic rounds of analysis are required: first, recognition of global priority areas by taxic diversity techniques; secondly, within any such area, analysis without taxic weighting (as being developed by Margules and his co-workers) to identify a network of reserves to contain all local taxa and ecosystems. The paper concludes with a brief discussion of some immediate prospects for development of a systematic approach to global conservation evaluation.