To begin Dr. Sarukhan's talk you can click here or read this brief overview, below, that provides links to the best places in the talk for specific topics.
Biodiversity comprises all forms of life, plants and animals and microorganisms.
Conservation biologists like to distinguish one additional level of diversity which is the cultural diversity of mankind. This is intimately linked to and constitutes an important influence on biological diversity. Biodiversity is equated with the number of different organisms present in a habitat . However it is very difficult to assess the number of species present on earth . I don't think we will ever know how these organisms function in the systems.