Configuration and distribution of biodiversity

Figure: The way biodiversity of the earth is probably divided among different taxonomic groups (after Purvis and Hector, 2000). The area of ​​each slice of the pie represents the number of species that is estimated to exist within each group; interior sectors represent the number of those species that have actually been catalogued.

The simplest question we can ask is: how much do we know, in purely descriptive terms, about biodiversity on our planet? The most honest answer is “very little ”. We do not even know how many species are hosted by our mother earth. The species described so far are almost 2 million (Purvis and Hector, 2000), but it is estimated that the total number of species on the planet is much larger. Different methods, valid primarily for terrestrial ecosystems, lead to the estimation that the number might be between 3 and 30 million. The most trusted value is 14 million (Hawksworth and Kalin-Arroyo, 1995). In particular, marine ecosystems are very little known. The marine species described so far are about 250,000, but recent studies (Bouchet, 2006) estimate that the oceans could accommodate up to 10 million species. In addition, the knowledge of the world biodiversity is not the same for the different taxonomic groups (see Fig. 4). It is very good as far as birds and mammals are concerned, but, for example, it is very bad with respect to bacteria. Insects are the true dominators of the earth because they have branched into an incredible number of species.

Biodiversity is not evenly distributed on earth. There are some regions that contain a very large number of different species that are endemic, namely present only in that particular geographical location. These regions (see Fig. 5) were called hotspots of biodiversity by Norman Myers in an article which is fundamental for conservation ecology (Myers et al., 2000). Of course, hotspots are very important because they require special attention by the global policies that are proposed to safeguard our planet's biodiversity. It is important to remark that Italy, with its great diversity of landscapes and ecosystems, is one of these hotspots, thus deserving appropriate conservation policies and management of its biological heritage.

Figure 5: The hotspots of biodiversity (Myers et al., 2000). They are defined as “areas that contain exceptional concentrations of endemic species and that are subject to an exceptional loss of habitat”.