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.
Diversity is more difficult to define than genetic or species diversity.
Ecosystems are an expression of different communities of species integrated into the physical environment. And biological diversity has not remained unalatered since life began on earth. Habitats are under threat all over the world. There are over one-half dozen main causes of biodiversity loss, of which, those related to partial or total destruction of habitats are the most serious. Biogeogrphical barriers have been broken producing problems of invasions of organisms.