CONCEPTUAL ASPECTS OF THE QUANTIFICATION OF THE EXTENT OF BIOLOGICAL DIVERSITY

This paper begins by asking to what extent numbers of species are an a dequate measure of biological diversity, either locally or globally; b oth for evolutionary understanding and for practical applications, bio diversity may often be better quantified at lower or higher levels, fr om genes to ecosystems. The subsequent discussion, however, focuses on species, and discusses questions that arise in estimating how many sp ecies there have ever been, how many there currently are in various ta xonomic groups, and how we may quantify the differing degrees of 'inde pendent evolutionary history' or 'taxonomic distinctiveness' in differ ent species or groups. I conclude with opinions about how the practica l task of identifying and recording species diversity might be better managed.