Environmental Problems, Their Causes, and Sustainability 1

Figure 9-12 Natural capital degradation: the human footprint on the earth’s land surface—in effect the sumof all ecological footprints (Figure 1-7, p. 10) of the human population. Colors represent the percentage of eacharea influenced by human activities. Excluding Antarctica and Greenland, human activities have directly affectedto some degree about 83% of the earth’s land surface and 98% of the area where it is possible to growrice, wheat, or maize. (Data from Wildlife Conservation Society and the Center for International Earth ScienceInformation Network at Columbia University [CIESIN]. Reprinted by permission.)PropertyComplexityEnergy sourceWaste productionNutrientsNet primaryproductivityNaturalSystemsBiologically diverseRenewable solarenergyLittle, if anyRecycledShared among manyspeciesHuman-DominatedSystemsBiologicallysimplifiedMostlynonrenewable fossilfuel energyHighOften lost or wastedUsed, destroyed, ordegraded to supporthuman activitiesFigure 9-13 Some typical characteristics of natural and human-dominated systems.We have used technology to alter muchof the rest of nature to meet our growingneeds and wants in nine major ways. One isreducing biodiversity by destroying, fragmenting,and degrading wildlife habitats. This happenswhen we clear forests, dig up grasslands, andfill in wetlands to grow food or to constructbuildings, highways, and parking lots.A second is reducing biodiversity by simplifyingand homogenizing natural ecosystems.Communities and ecosystems dominated byhumans tend to have fewer species and fewercommunity interactions than do undisturbedecosystems. When we plow grasslands andclear forests, we often replace thousands ofinterrelated plant and animal species withone crop or one kind of tree—called a monoculture.Then we spend a lot of time, energy,and money trying to protect such monoculturesagainst threats such as invasions by opportunistspecies of plants (weeds) and pests—mostly insects, to which a monoculture cropis like an all-you-can-eat restaurant. Anotherthreat is invasions by pathogens—fungi,viruses, or bacteria—that harm the plantsand animals we want to raise.172 CHAPTER 9 Population Ecology