Biodiversity and ecosystems are closely related concepts. Biodiversity is defined by the Convention on Biological Diversity as:

“the variability among living organisms from all sources including, inter alia, 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”.

It is the concepts of diversity and variability which are important. There are many ways of considering this diversity, such as the number and abundance of species, their distribution in an area, and their different types of interactions in an ecological sense.

A major area of current research is how important are different aspects of biodiversity in the functioning of ecosystems and the benefits people obtain from them. It is recognised that biodiversity in the broad sense affects the amounts, speed and timing of the flows of energy and materials through ecosystems. The most dramatic changes in ecosystem functioning are likely to come from altered composition of food webs, such as the loss of predators, and from declines of locally abundant species rather than the loss of already rare species.