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According to the convention on Biological Diversity, "biological diversity means the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems" (UNEP, 1994). The term ´biodiversity` thus refers to the variety of all life on earth, and explicitly recognises how the interaction of the different components of ecosystems result in the provision of essential ecosystem services on the one hand, and social and recreational opportunities on the other, including being a source of inspiration and cultural identity (Commonwealth of Australia, 1996).
A number of concepts have been developed in recent years relating to indicators of or principles for biodiversity management, including ¨ecosystem integrity¨, ¨ecosystem health¨, ¨sustainability¨, and ¨resilience¨ (the ability of an ecosystem to withstand stresses and shocks). The variety of concepts and definitions that abound indicates the difficulties facing any attempts to establish a practical, working definition of biological diversity. Perhaps one of the simplest and most widely accepted definitions used is the conservation of the maximum number of species. But even here there are difficulties as it is not clear what actually constitutes a species. Some common concepts for differentiating species have been identified by Brookes (1998) as:
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biological species concept- defines a species as a group of interbreeding populations isolated from other such groups;
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morphological species definition- defines a species according to a given set of common features;
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evolutionary species concept- defines a species by its shared evolutionary history; and
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genotypic cluster definition- uses genetic ¨gaps¨ to distinguish between species.
Each of these definitions tries to isolate a species out from the wider concepts of ecosystem and biodiversity, but the variety of definitions in use indicates the difficulties inherent in such an exercise.
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