The measurement of species diversity, and its relationship to community stability.

Shaw, Kathleen Muriel (1981). The measurement of species diversity, and its relationship to community stability. BPhil thesis The Open University.



Species diversity is hard to define either as a single attribute or as two separate concepts of number of species present in a community and the equitability of the distribution of individuals amongst the species. While it is easy to produce a list of conditions that should be satisfied by any measure agreeing with our intuitive conception of equitability, some of these conditions are mutually contradictory. It is hardly surprising therefore that no single measure of diversity or equitability is perfectly satisfactory and that different measures may produce conflicting orderings of the same set of communities. Chapter 1 gives an introductory survey of the various ways of measuring diversity and equitability - by a single function of the species abundances, by a parameter of a distribution fitted to the observed distribution of species abundances, or by defining a partial ordering of communities. I comment on the principles behind a definition of diversity or equitability, and on the ideas to be considered when choosing a suitable measure. In Chapter 2 I first discuss the ways in which the environment may affect the diversity of communities able to live there, and present some of the experimental evidence. Secondly I discuss the possibility that the diversity of a community may affect its ability to survive in a changing environment. Here experimental evidence is sparse and contradictory. Therefore, in Chapter 5, I study this problem further by computer simulation, and show that factors other than diversity play an important part. In my pilot study of only two species the main effect on stability is that of changing the equilibrium number of individuals. No diversity effect could be detected. Perhaps more species are needed, but even a three-species simulation involves considerably more variables if it is to be investigated fully.

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