Biodiversity is the variety of life and the ramge of living organisms to be found everywhere.
We normally talk about this in terms of individual habitats. These are the areas in which an organism (or group of organisms) live, and is usually where the organism is best adatpted for survival.
A group of organisms that share characteristics on a physiological and genetic level, which can interbreed to produce fertile offspring, are called a species.
There are two measures of biodiversity:
Species richness is a measure of the number of species present in a habitat.
Species evenness is a measure of the balance of the various species in a habitat. This takes into account the numbers of individuals of each species.