Levels of biodiversity

Edward Wilson popularised 'biodiversity' as covering every level of biological organisation, from individual populations up to entire biomes, and the chapter organises this into three levels (Fig. 12.1): genetic, species, and community/ecosystem diversity. Genetic diversity is the variation in genetic make-up — the number and types of genes — both between distinct species and within a single species, including variation between separate populations of that species; it is measurable using molecular techniques, and India alone holds more than 50,000 genetic variants of paddy and 1,000 of mango. The medicinal plant Rauwolfia vomitoria illustrates this directly: growing across different ranges of the Himalayas, it shows measurable differences in the potency and concentration of its active ingredient, reserpine, purely due to genetic diversity — variation that also gives rise to distinct races, varieties and subspecies, and helps species adapt to changing environmental conditions. Species diversity is the variety and richness of species within any habitat; species richness (the number of species per unit area at a given time) is its standard measure, and the Western Ghats are cited as having greater amphibian species diversity than the Eastern Ghats (Fig. 12.1a). This level is further split into three indices: Alpha diversity (the number of taxa within one particular area, community or ecosystem), Beta diversity (the species diversity between two adjacent ecosystems, found by comparing the species unique to each), and Gamma diversity (the diversity of habitats across an entire landscape or geographical region). Community/ecosystem diversity is the variety of habitats, biotic communities and ecological processes acr …