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. Another important factor is exploitation of natural resources. Climate change can also effect biological diversity in several ways. Finally, rapid population growth effects diversity through the use of the world's resources.