What must we know about biodiversity to conserve it?
Stuart Pimm is the Doris Duke Chair of Conservation Ecology at the Nicholas School of the Environment at Duke University. His research covers the reasons why species become extinct, how fast they do so, global patterns of habitat loss and species extinction and, importantly, the management consequences of this research. He was awarded the Tyler Prize for Environmental Achievement (2010), the Dr. A.H. Heineken Prize for Environmental Sciences (2006), the Edward T. LaRoe III Memorial Award (2006), and the William Proctor Prize for Scientific Achievement (2007).
The salient feature of biodiversity is how fast we are losing it. We measure extinctions much as the same way as a human death rate — deaths per thousand people per year — except with slightly different units. Extinctions currently run several hundred extinctions per million species per year. Moreover, we have a rough idea from the fossil record and from the rates at which species diversify genetically, that background rates of extinction are on the order of one extinction per ten million species per year. Such is the impact of human actions. We know much about the biogeography of extinction and its causes. On land, most plant and animal species live in the moist tropical forests of the world. The species at greatest risk of extinction fall into two broad classes. First, there are those that are large-bodied — lions and tigers and bears (and sharks in the oceans) for example. Second, are the much greater number of smaller species that have small geographical ranges. Across all taxa, there are many species small geographical ranges. The statistical distribution of range sizes is such that while the average range size of a group of species might be quite large, the median — below which 50% of species are — can be small in comparison. Half of all amphibian species have ranges smaller than ~4,000 km2 or so, for example. Recently described species tend to have still smaller ranges. These small-ranged species are highly concentrated geographically into biodiversity hotspots, places such as the northern Andes, the coastal forests of Brazil, the fynbos of South Africa, Madagascar, and the Philippines. Similar principles apply in the oceans. These results are actionable science. To reduce extinction rates, we need to concentrate on these hotspots — areas that cover only about 10% of the land surface. Practical conservation actions require downscaling from these regions to areas measured in tens or hundreds of square kilometres for that is the size of most protected areas. In all of these hotspots, the remaining habitats are massively fragmented. Species are lost quickly from isolated fragments. This suggests re-establishing the connections between isolated fragments by acquiring the degraded land between then and restoring its natural vegetation is likely to be a cost-effective solution to reducing extinction rates. That’s exactly what SavingSpecies does. Visit us at http://www.savingspecies.org.