This process is referred to as natural selection and genetic diversity is a very important component of this process. When introducing species diversity it is easiest to start with an operational definition of a species. Species diversity is a quantifiable measure of all the individuals of all the species that exist in a given area. Species usually occur throughout their range in geographically and temporally separate groups referred to as populations. In addition, Coyote occur throughout the United States but the individuals that live in the Great Basin are considered members of their own population.
All species are members of some ecological community.
A community is a group of species that live and interact in the same physical conditions. There can be more than one food web present in a community. For example, in a riparian forest there is a food web cycling in the stream almost independent of the one cycling in the terrestrial portion. The cycling of food webs can be a very delicate process of checks and balances that limit the population size of any given species in the web. When all the individuals of a species disappear, food webs may be thrown out of balance and some species may increase to the point were they deplete their own resources causing other species to disappear as well.