Species diversity
An important attribute of a community is its species diversity. The diversity is calculated both by the number of species (richness) and the relative abundance of each species (evenness). The greater the number of species and more even their distribution the greater is the species diversity.
It is important to realise that species diversity and dominance are interrelated. Communities with one or a few dominant species are characterised by low species diversity whereas communities where no single species is truly dominant and individuals are equally distributed among all species. are charactensed by high species diversity.
Diversity is also related to the stability of the community. A stable community is one which is able to return to its original condition after being disturbed in some way. Communities with high species diversity are comparatively more stable because many alternative pathways exist in such communities to enable the individuals to obtain the required energy and nutrients. To put it differently, the presence of a large number of species would mean that if one species disappears or declines, its function and place can be assumed at least in part by another. It is now however, increasingly realised that in some situations greater diversity does not necessarily result in greater stability. Stability is more dependent on the number of well adapted species than on the total number of species present.
Communities created by man such as lawns, or agricultural fields are very unstable and require great deal of constant manipulation and maintenance.