Biodiversity is the variety of life on earth and includes variation at all levels of biological
organisation from genes to species to ecosystems. Genetic, organismal and ecological
diversity are all elements of biodiversity with each including a number of components (Table
1) (Gaston & Spicer 2004).
All of these elements of biodiversity have led to a large number of formal definitions; Delong
(1996) reviewed 85 different definitions. An important and widely used definition is that
included within the Convention on Biological Diversity (CBD). This treaty was signed by over
150 nations at the United Nations Conference on Environment and Development, held in Rio
de Janeiro, Brazil, in 1992. It defines biodiversity as “the variability among living organisms
from all sources including, inter alia [among other things], terrestrial, marine and other aquatic
ecosystems and the ecological complexes of which they are part; this includes diversity within
species, between species and of ecosystems”.