Environmental Problems, Their Causes, and Sustainability 1

each of these three species estimates if the extinctionrate is 1% a year?According to researchers Edward O. Wilson andStuart Primm, at a 1% extinction rate at least 20% ofthe world’s current animal and plant species could begone by 2030 and 50% could vanish by the end of thiscentury. In the words of biodiversity expert NormanMyers, “Within just a few human generations, weshall—in the absence of greatly expanded conservationefforts—impoverish the biosphere to an extentthat will persist for at least 200,000 human generationsor twenty times longer than the period since humansemerged as a species.”Most biologists consider extinction rates of 0.1–1%to be conservative estimates for several reasons. First,both the rate of species loss and the extent of biodiversityloss are likely to increase during the next 50–100years because of the projected exponential growth ofthe world’s human population and per capita resourceuse. In other words, the size of our already large ecologicalfootprint (Figure 1-7, p. 10 and Figure 9-12,p. 172) is likely to increase.Second, current and projected extinction rates aremuch higher than the global average in parts of theworld that are endangered centers of biodiversity.Conservation biologists estimate that such biologicallyrich areas could lose one-fourth to one-half of their estimatedspecies within a few decades. They urge us tofocus our efforts on slowing the much higher rates ofextinction in such hot spots (Figure 11-24, p. 219) as thebest and quickest way to protect much of the earth’sbiodiversity from being lost prematurely.Third, we are eliminating, degrading, and simplifyingmany biologically diverse environments—suchas tropical forests, tropical coral reefs, wetlands, andestuaries—that serve as potential colonization sites forthe emergence of new species. Thus, in addition to increasingthe rate of extinction, we may also be limitinglong-term recovery of biodiversity by reducing therate of speciation for some types of species. In otherwords, we are also creating a speciation crisis. SeeNorman Myers Guest Essay on this topic on the websitefor this chapter.Philip Levin, Donald Levin, and other biologistsalso argue that the increasing fragmentation and disturbanceof habitats throughout the world may increasethe speciation rate for rapidly reproducing opportunistspecies such as weeds, rodents, and cockroaches andother insects. Thus the real threat to biodiversity fromcurrent human activities may not be a permanent declinein the number of species but a long-term erosion inthe earth’s variety of species and habitats.Some people, most of them not biologists, say thecurrent estimated extinction rates are too high and arebased on inadequate data and models. Researchersagree that their estimates of extinction rates are basedon inadequate data and sampling. They continuallystrive to get better data and improve the models theyuse to estimate extinction rates.However, they point to clear evidence that humanactivities have increased the rate of species extinctionand that this rate is likely to rise. According to thesebiologists, arguing over the numbers and waiting toget better data and models should not be used as excusesfor inaction. They call for us to implement a precautionarystrategy now to help prevent a significantdecrease in the earth’s genetic, species, ecological, andfunctional diversity.To these biologists, we are not heeding the warningof Aldo Leopold about preserving biodiversity aswe tinker with the earth: “To keep every cog andwheel is the first precaution of intelligent tinkering.”12-2 IMPORTANCE OF WILD SPECIESWhy Should We Preserve Wild Species? TheyHave ValueWe should not cause the premature extinction ofspecies because of the economic and ecologicalservices they provide.So what is all the fuss about? If all species eventuallybecome extinct, why should we worry about losing afew more because of our activities? Does it matter thatthe passenger pigeon, the 80–100 remaining Floridapanthers, or some unknown plant or insect in a tropicalforest becomes prematurely extinct because of ouractivities?We know that new species eventually evolve totake the place of ones lost through extinction spasms,mass depletions, or mass extinctions. So why shouldwe care if we speed up the extinction rate over the next50–100 years? The answer is that it will take at least5 million years for speciation to rebuild the biodiversity weare likely to destroy during this century!Conservation biologists and ecologists say weshould act now to prevent the premature extinction ofspecies because of their instrumental value based ontheir usefulness to us in the form of economic and ecologicalservices. For example, species provide economicvalue in the form of food crops, fuelwood andlumber, paper, and medicine (Figure 11-17, p. 211).Another instrumental value is the genetic informationin species. Genetic engineers use this informationto produce new types of crops (Figure 5-11, p. 98) andfoods and edible vaccines for viral diseases such ashepatitis B. Carelessly eliminating many of the speciesmaking up the world’s vast genetic library is likeburning books before we read them. Wild species alsoprovide a way for us to learn how nature works andsustains itself.The earth’s wild plants and animals also provideus with recreational pleasure. Each year Americanshttp://biology.brookscole.com/miller14229