Environmental Problems, Their Causes, and Sustainability 1

By contrast, grasslands are much less diverse thanmost forests and have low inertia because they burneasily. However, because most of their plant matter isstored in underground roots, these ecosystems havehigh resilience and recover quickly. Grassland can bedestroyed only if its roots are plowed up and somethingelse is planted in its place, or if it is severelyovergrazed by livestock or other herbivores. Bad news.We have been doing both of these things in somegrassland areas for many decades.Another difficulty is that populations, communities,and ecosystems are rarely, if ever, at equilibrium.Instead, nature is in a continuing state of disturbance,fluctuation, and change.Why Should We Bother to ProtectNatural Systems? The PrecautionaryPrincipleSometimes we should take precautionary measures toprevent serious harm even if some of the cause-andeffectrelationships have not been established.Some developers argue that if biodiversity does notnecessarily lead to increased ecological stability, thereis no point in trying to preserve and manage oldgrowthforests and other ecosystems. They concludethat we should cut down diverse old-growth forests,use the timber resources, and replace the forests withtree plantations of single tree species. Furthermore,they say, we should convert most of the world’s grasslandsto crop fields, drain and develop inland wetlands,dump our toxic and radioactive wastes into thedeep ocean, and not worry about the premature extinctionof species.Ecologists point out that just because a system isnot in equilibrium or balance does not mean that itcannot suffer from environmental degradation. Theypoint to overwhelming evidence that human disturbancesare disrupting some of the ecosystem servicesthat support and sustain all life and all economies.They contend that our ignorance about the effects ofour actions means we need to use great caution inmaking potentially harmful changes to communitiesand ecosystems on the fairly short-term time framethat concerns us.As an analogy, we know that eating too much ofcertain types of foods and not getting enough exercisecan greatly increase our chances of a heart attack, diabetes,and other disorders. But the exact connectionsbetween these health problems, chemicals in variousfoods, exercise, and genetics are still under study andoften debated. We could use this uncertainty and unpredictabilityas an excuse to continue overeating andnot exercising. But the wise course is to eat better andexercise more to help prevent potentially serious healthproblems.This approach is based on the precautionary principle:When there is evidence that a human activitycan harm our health or bring about changes in environmentalconditions that can affect our economies orquality of life, we should take measures to preventharm even if some of the cause-and-effect relationshipshave not been fully established scientifically. It isbased on the commonsense idea behind many adagessuch as “Better safe than sorry,” “Look before youleap,” “First, do no harm,” and “Slow down for speedbumps.”The precautionary principle makes sense, but itcan be taken too far. If we do not take some risks, wewould never learn much or discover what works andwhat does not.The message is that we should take some risks butalways think carefully about the possible short- andlong-term expected and unintended effects (Figure 3-4,p. 38). Using the precautionary principle comes inwhen the potential risks seem too great or we have littleinformation about the possible risks. Then it is timeto step back, think about what we are doing, and domore research.In this chapter we have seen how interactionsamong organisms in a community determine theirabundances and distributions. Such interactions alsoserve as agents of natural selection on one anotherthrough coevolution. They also have significant effectson the structure and function of the ecosystems inwhich these organisms live. Everything is connected.No part of the world is what it was before there were humans.LAWRENCE B. SLOBODKINCRITICAL THINKING1. How would you respond to someone who claims it isnot important to protect areas of temperate and polarbiomes because most of the world’s biodiversity is in thetropics?2. Why is the species diversity of a large island usuallyhigher than that on a smaller island?3. Why are predators generally less abundant than theirprey?4. What would you do if large numbers of cockroachesinvaded your home? See whether you can come up withan ecological rather than a chemical (pesticide) approachto this problem.5. How would you determine whether a particularspecies found in a given area is a keystone species?6. Describe how evolution can affect predator–preyrelationships.7. How would you reply to someone who argues that(a) we should not worry about our effects on natural systemsbecause succession will heal the wounds of humanhttp://biology.brookscole.com/miller14161