There are three scales that shape the concept of biodiversity under study. the first is genetic diversity, involving community, population, organism, cell and molecule. the second is taxonomic diversity, which involves, kingdom, phylum, class, order, family, genus, species and subspecies. The third is ecological diversity, involving biosphere, biome, landscape, ecosystem and habitat-niche.
The conservation status of most species is not known in detail but two large animal groups - mammals and birds - have been comprehensively assessed and may be representative of the status of biodiversity in general. In 1996, 25 per cent of the world's approximately 4 630 mammal species, and 11 per cent of the 9 675 bird species were assessed as globally threatened - that is, at significant risk of total extinction (IUCN 1996). Countless other species, although not yet globally threatened, now exist in reduced numbers and as fragmented populations, and many of these are threatened with extinction at national level.
2. Existing biological knowledge is patchy and thus substantially more research is required to improve understanding. In particular, the interactions between biological and social processes are poorly understood, as are the causes underlying the decline in biodiversity.