The word biodiversity is a relatively new one that is a shortened version of the term ‘biological diversity'. In its simplest form, biodiversity refers to the number and variety of earth's life forms.
This not only includes all of the different species (types) of familiar plants and animals but also includes less well known organisms such as bacteria and other microorganisms.
To date biologists have counted almost 1.8 million different species of living organisms. However, this count is only the tip of the iceberg and estimates of the number of different species on earth vary from 5 million to 100 million with 30 million being a widely accepted figure.
A broader definition of biodiversity goes beyond simply counting species to include genetic variety and variability within each species and the ecological complexes in which they occur. Hence a widely accepted definition of biodiversity states that:
Biodiversity is the variety of all life forms; the different species of plants, animals and microorganisms, the genes they contain and the ecosystems of which they form a part.
As a result of this broadened definition, scientists often talk about three levels of biodiversity:
Genetic diversity - refers to the genetic variety and variability within each species.
Species diversity - the number of different species living on earth. At present almost 1.8 million species have been discovered and described by scientists.
Ecosystem diversity - refers to variety in the combination of species that form ecosystems such as ponds, coral reefs, forests or grasslands.