The Measurement of Species Diversity

Inspired significantly by the provocative papers of MacArthur (34, 35, 38) and Hutchinson (22), ecologists over the past twenty years have devoted considerable energy to the explanation of patterns of diversity in ecologic systems. Despite considerable interest, however, no generally accepted definition of diversity has emerged. "Diversity per se does not exist," was the contention of Hurlbert (20), who suggested abandoning the term because of the multiplicity of meanings and interpre­ tations attached to it. MacArthur (37) also considered the term had outlived its usefulness, and Eberhardt (10), Austin (2), and McIntosh (40) all complained of the lack of a definition. Eberhardt considered that diversity "mostly suggests a consider­ able confusion of concepts, definitions, models, and measures (or indices)." If diver­ sity is to continue to play a productive role in ecological investigations, agreement is needed on the definitions of the many constituent concepts included in its current application. At the community level of synthesis many phenomena are complex and open to multiple interpretation. Consequently, many authors have suggested diversity in­ dices appropriate for their own studies, no one of which can be considered a priori correct for general application (12, 19,20,32,40). Diversity, in essence, has always been defined by the indices used to measure it, and this has not fostered the sort of uniformity which allows the clear statement of ideas and hypotheses. Progress in ecology, as in all science, depends upon precise and unambiguous definition of terms and concepts (2, 40, 44). The present contribution attempts to define in a precise, but still generalized I1\anner, what is or should be meant by the many terms sur­ rounding the concept-cluster diversity. Guidelines are also suggested for the applica­ tion of the many ayailable diversity indices.