Environmental Problems, Their Causes, and Sustainability 1

Florida manatee Northern spotted owl Gray wolfFlorida panther Bannerman’s turaco(threatened)(Africa)Devil’s hole pupfish Snow leopardSymphoniaBlack-footed ferret Utah prairie dog(Central Asia)(Madagascar)Ghost bat(Australia)California condorBlack lace cactusBlack rhinoceros(Africa)Oahu tree snailHow Do Biologists Estimate Extinction Rates?Peering into a Cloudy Looking GlassScientists use measurements and models to estimateextinction rates.Evolutionary biologists estimate that 99.9% of all speciesthat ever existed are now extinct because of a combinationof background extinction, mass extinctions,and mass depletions taking place over thousands tomillions of years. Biologists also talk of an extinctionspasm, in which large numbers of species are lost over aperiod of a few centuries or at most 1,000 years.Biologists trying to catalog extinctions have threeproblems. First, the extinction of a species typicallytakes such a long time that it is not easy to document.Second, we have identified only about 1.4–1.8 million ofthe world’s estimated 5–100 million species. Third, weknow little about most of the species we have identified.The truth is we do not know how many speciesare becoming extinct each year mostly because of ouractivities. But scientists do the best they can with thetools they have to estimate past and projected futureextinction rates.One approach is to study past records documentingthe rate at which mammals and birds have becomeextinct since we came on the scene and comparing thiswith the fossil records of such extinctions prior to ourarrival. For example, there is a detailed study on extinctionof Pacific island birds by early human colonists.Since the 1960s the International Union for the Conservationof Nature and Natural Resources (IUCN)—alsoknown as the World Conservation Union—has kepthttp://biology.brookscole.com/miller14227