A measure of the as well as of organism types found within a community.
Generally the greater the species diversity of a community then the healthier that community/ecosystem. This can be viewed both in terms of cause and effect. That is, the healthier an ecosystem then generally the greater its species diversity, but also the greater its species diversity the healthier a community.
The reason for this is because the taking over of a community by a few types of organisms tends to negatively impact to a large extent because of reductions in species diversity (that is, there is are reduction in the number of functions an ecosystem can perform because of a lower diversity of functional components).
In addition, the taking over of a community by a few types of organisms can have the effect of altering an ecosystem in certain ways that it is no longer suitable for other species (which, in a sense, represents the opposite of ecological facilitation). Thus, a poorly functioning ecosystem tends to lose species and losing species tends to negatively impact ecosystem functioning.
See also .