Sinh học - Chapter 56: Conservation biology and restoration ecology

Chapter 56Conservation Biology and Restoration EcologyOverview: Striking Gold1.8 million species have been named and describedBiologists estimate 10–200 million species exist on EarthTropical forests contain some of the greatest concentrations of species and are being destroyed at an alarming rateHumans are rapidly pushing many species toward extinctionFig. 56-1Fig. 56-2Conservation biology, which seeks to preserve life, integrates several fields:EcologyPhysiology Molecular biologyGeneticsEvolutionary biologyRestoration ecology applies ecological principles to return degraded ecosystems to conditions as similar as possible to their natural stateConcept 56.1: Human activities threaten Earth’s biodiversityRates of species extinction are difficult to determine under natural conditionsThe high rate of species extinction is largely a result of ecosystem degradation by humansHumans are threatening Earth’s biodiversityThree Levels of BiodiversityBiodiversity has three main components:Genetic diversitySpecies diversityEcosystem diversityFig. 56-3Genetic diversity in a vole populationSpecies diversity in a coastal redwood ecosystemCommunity and ecosystem diversityacross the landscape of an entire regionGenetic DiversityGenetic diversity comprises genetic variation within a population and between populationsSpecies DiversitySpecies diversity is the variety of species in an ecosystem or throughout the biosphereAccording to the U.S. Endangered Species Act: An endangered species is “in danger of becoming extinct throughout all or a significant portion of its range”A threatened species is likely to become endangered in the foreseeable futureConservation biologists are concerned about species loss because of alarming statistics regarding extinction and biodiversityGlobally, 12% of birds, 20% of mammals, and 32% of amphibians are threatened with extinctionFig. 56-4(a) Philippine eagleYangtze Riverdolphin(b)Javanrhinoceros(c)Fig. 56-4a(a) Philippine eagleFig. 56-4b(b) Yangtze River dolphinFig. 56-4c(c) Javan rhinocerosEcosystem DiversityHuman activity is reducing ecosystem diversity, the variety of ecosystems in the biosphereMore than 50% of wetlands in the contiguous United States have been drained and converted to other ecosystemsFig. 56-5Biodiversity and Human WelfareHuman biophilia allows us to recognize the value of biodiversity for its own sakeSpecies diversity brings humans practical benefitsBenefits of Species and Genetic DiversityIn the United States, 25% of prescriptions contain substances originally derived from plantsFor example, the rosy periwinkle contains alkaloids that inhibit cancer growthFig. 56-6The loss of species also means loss of genes and genetic diversityThe enormous genetic diversity of organisms has potential for great human benefitEcosystem ServicesEcosystem services encompass all the processes through which natural ecosystems and their species help sustain human lifeSome examples of ecosystem services:Purification of air and waterDetoxification and decomposition of wastesCycling of nutrientsModeration of weather extremesThree Threats to BiodiversityMost species loss can be traced to three major threats:Habitat destructionIntroduced speciesOverexploitationHabitat LossHuman alteration of habitat is the greatest threat to biodiversity throughout the biosphereIn almost all cases, habitat fragmentation and destruction lead to loss of biodiversityFor example In Wisconsin, prairie occupies <0.1% of its original areaAbout 93% of coral reefs have been damaged by human activitiesFig. 56-7Introduced SpeciesIntroduced species are those that humans move from native locations to new geographic regionsWithout their native predators, parasites, and pathogens, introduced species may spread rapidlyIntroduced species that gain a foothold in a new habitat usually disrupt their adopted communitySometimes humans introduce species by accident, as in case of the brown tree snake arriving in Guam as a cargo ship “stowaway”Fig. 56-8(a) Brown tree snake(b) KudzuFig. 56-8a(a) Brown tree snakeFig. 56-8b(b) KudzuHumans have deliberately introduced some species with good intentions but disastrous effectsAn example is the introduction of kudzu in the southern United StatesOverexploitationOverexploitation is human harvesting of wild plants or animals at rates exceeding the ability of populations of those species to reboundOverexploitation by the fishing industry has greatly reduced populations of some game fish, such as bluefin tunaFig. 56-9DNA analysis can help conservation biologists to identify the source of illegally obtained animal productsConcept 56.2: Population conservation focuses on population size, genetic diversity, and critical habitatBiologists focusing on conservation at the population and species levels follow two main approaches: The small-population approachThe declining-population approachSmall-Population ApproachThe small-population approach studies processes that can make small populations become extinctThe Extinction VortexA small population is prone to positive-feedback loops that draw it down an extinction vortexThe key factor driving the extinction vortex is loss of the genetic variation necessary to enable evolutionary responses to environmental changeFig. 56-10InbreedingSmallpopulationGeneticdriftLowerreproductionHighermortalitySmallerpopulationReduction inindividualfitness andpopulationadaptabilityLoss ofgeneticvariabilityCase Study: The Greater Prairie Chicken and the Extinction VortexPopulations of the greater prairie chicken were fragmented by agriculture and later found to exhibit decreased fertilityTo test the extinction vortex hypothesis, scientists imported genetic variation by transplanting birds from larger populationsThe declining population rebounded, confirming that low genetic variation had been causing an extinction vortexFig. 56-11TranslocationYear(a) Population dynamicsNumber of male birds20015010050019701975198519901995100Eggs hatched (%)90807060504030Years(b) Hatching rate1970–’74’75–’79’80–’84’85–’89’90’93–’971980RESULTSFig. 56-11aTranslocationYear(a) Population dynamicsNumber of male birds200150100500197019751985199019951980RESULTSFig. 56-11b100Eggs hatched (%)90807060504030Years(b) Hatching rate1970–’74’75–’79’80–’84’85–’89’90’93–’97RESULTSMinimum Viable Population SizeMinimum viable population (MVP) is the minimum population size at which a species can surviveThe MVP depends on factors that affect a population’s chances for survival over a particular timeEffective Population SizeA meaningful estimate of MVP requires determining the effective population size, which is based on the population’s breeding potentialEffective population size Ne is estimated by:where Nf and Nm are the number of females and the number of males, respectively, that breed successfully4NfNmNf + NmNe = Case Study: Analysis of Grizzly Bear PopulationsOne of the first population viability analyses was conducted as part of a long-term study of grizzly bears in Yellowstone National ParkThis grizzly population is about 400, but the Ne is about 100The Yellowstone grizzly population has low genetic variability compared with other grizzly populationsIntroducing individuals from other populations would increase the numbers and genetic variationFig. 56-12Declining-Population ApproachThe declining-population approachFocuses on threatened and endangered populations that show a downward trend, regardless of population sizeEmphasizes the environmental factors that caused a population to declineSteps for Analysis and InterventionThe declining-population approach involves several steps:Confirm that the population is in declineStudy the species’ natural historyDevelop hypotheses for all possible causes of declineTest the hypotheses in order of likeliness Apply the results of the diagnosis to manage for recoveryCase Study: Decline of the Red-Cockaded WoodpeckerRed-cockaded woodpeckers require living trees in mature pine forestsThey have a complex social structure where one breeding pair has up to four “helper” individualsThis species had been forced into decline by habitat destructionFig. 56-13(a) Forests with low undergrowth(b) Forests with high, dense undergrowthRed-cockadedwoodpeckerFig. 56-13a(a) Forests with low undergrowthFig. 56-13b(b) Forests with high, dense undergrowthFig. 56-13cRed-cockadedwoodpeckerIn a study where breeding cavities were constructed, new breeding groups formed only in these sitesBased on this experiment, a combination of habitat maintenance and excavation of breeding cavities enabled this endangered species to reboundWeighing Conflicting DemandsConserving species often requires resolving conflicts between habitat needs of endangered species and human demandsFor example, in the U.S. Pacific Northwest, habitat preservation for many species is at odds with timber and mining industriesManaging habitat for one species might have positive or negative effects on other speciesConcept 56.3: Landscape and regional conservation aim to sustain entire biotasConservation biology has attempted to sustain the biodiversity of entire communities, ecosystems, and landscapesEcosystem management is part of landscape ecology, which seeks to make biodiversity conservation part of land-use planningLandscape Structure and BiodiversityThe structure of a landscape can strongly influence biodiversityFragmentation and EdgesThe boundaries, or edges, between ecosystems are defining features of landscapesSome species take advantage of edge communities to access resources from both adjacent areasFig. 56-14(a) Natural edges(b) Edges created by human activityFig. 56-14a(a) Natural edgesFig. 56-14b(b) Edges created by human activityThe Biological Dynamics of Forest Fragments Project in the Amazon examines the effects of fragmentation on biodiversityLandscapes dominated by fragmented habitats support fewer species due to a loss of species adapted to habitat interiorsFig. 56-15Corridors That Connect Habitat FragmentsA movement corridor is a narrow strip of quality habitat connecting otherwise isolated patchesMovement corridors promote dispersal and help sustain populationsIn areas of heavy human use, artificial corridors are sometimes constructedFig. 56-16Establishing Protected AreasConservation biologists apply understanding of ecological dynamics in establishing protected areas to slow the loss of biodiversityMuch of their focus has been on hot spots of biological diversityFinding Biodiversity Hot SpotsA biodiversity hot spot is a relatively small area with a great concentration of endemic species and many endangered and threatened speciesBiodiversity hot spots are good choices for nature reserves, but identifying them is not always easyVideo: Coral ReefFig. 56-17EquatorTerrestrial biodiversityhot spotsMarine biodiversityhot spotsPhilosophy of Nature ReservesNature reserves are biodiversity islands in a sea of habitat degraded by human activityNature reserves must consider disturbances as a functional component of all ecosystemsAn important question is whether to create fewer large reserves or more numerous small reservesOne argument for extensive reserves is that large, far-ranging animals with low-density populations require extensive habitatsSmaller reserves may be more realistic, and may slow the spread of disease throughout a populationFig. 56-18Kilometers050100MONTANAIDAHOMONTANAWYOMINGYellowstone National ParkYellowstone R.Shoshone R.Grand TetonNational ParkSnake R.IDAHOWYOMINGBiotic boundary forshort-term survival;MVP is 50 individuals.Biotic boundary forlong-term survival;MVP is 500 individuals.Zoned ReservesThe zoned reserve model recognizes that conservation often involves working in landscapes that are largely human dominatedA zoned reserve includes relatively undisturbed areas and the modified areas that surround them and that serve as buffer zones Zoned reserves are often established as “conservation areas”Costa Rica has become a world leader in establishing zoned reservesFig. 56-19NicaraguaCostaRicaCARIBBEAN SEAPACIFIC OCEANPanamaNational park landBuffer zone(a) Zoned reserves in Costa Rica(b) Schoolchildren in one of Costa Rica’s reservesFig. 56-19aNicaraguaCostaRicaCARIBBEAN SEAPACIFIC OCEANPanamaNational park landBuffer zone(a) Zoned reserves in Costa RicaFig. 56-19b(b) Schoolchildren in one of Costa Rica’s reservesSome zoned reserves in the Fiji islands are closed to fishing, which actually improves fishing success in nearby areasThe United States has adopted a similar zoned reserve system with the Florida Keys National Marine SanctuaryFig. 56-20FLORIDAGULF OF MEXICO50 kmFlorida Keys NationalMarine SanctuaryConcept 56.4: Restoration ecology attempts to restore degraded ecosystems to a more natural stateGiven enough time, biological communities can recover from many types of disturbancesRestoration ecology seeks to initiate or speed up the recovery of degraded ecosystemsA basic assumption of restoration ecology is that most environmental damage is reversibleTwo key strategies are bioremediation and augmentation of ecosystem processesFig. 56-21(a) In 1991, before restoration(b) In 2000, near the completion of restorationFig. 56-21a(a) In 1991, before restorationFig. 56-21b(b) In 2000, near the completion of restorationBioremediationBioremediation is the use of living organisms to detoxify ecosystemsThe organisms most often used are prokaryotes, fungi, or plantsThese organisms can take up, and sometimes metabolize, toxic moleculesFig. 56-22(a) Unlined pits filled with wastes containing uranium(b) Uranium in groundwaterDays after adding ethanolConcentration ofsoluble uranium (µM)6543210050100150200250300350400Fig. 56-22a(a) Unlined pits filled with wastes containing uraniumFig. 56-22b(b) Uranium in groundwaterDays after adding ethanolConcentration ofsoluble uranium (µM)6543210050100150200250300350400Biological AugmentationBiological augmentation uses organisms to add essential materials to a degraded ecosystemFor example, nitrogen-fixing plants can increase the available nitrogen in soilExploring RestorationThe newness and complexity of restoration ecology require that ecologists consider alternative solutions and adjust approaches based on experienceFig. 56-23aEquatorFig. 56-23bTruckee River, NevadaFig. 56-23cKissimmee River, FloridaFig. 56-23dTropical dry forest, Costa RicaFig. 56-23eRhine River, EuropeFig. 56-23fSucculent Karoo, South AfricaFig. 56-23gCoastal JapanFig. 56-23hMaungatautari, New ZealandConcept 56.5: Sustainable development seeks to improve the human condition while conserving biodiversityThe concept of sustainability helps ecologists establish long-term conservation prioritiesSustainable Biosphere InitiativeSustainable development is development that meets the needs of people today without limiting the ability of future generations to meet their needsThe goal of the Sustainable Biosphere Initiative is to define and acquire basic ecological information for responsible development, management, and conservation of Earth’s resourcesSustainable development requires connections between life sciences, social sciences, economics, and humanitiesCase Study: Sustainable Development in Costa RicaCosta Rica’s conservation of tropical biodiversity involves partnerships between the government, other organizations, and private citizensHuman living conditions (infant mortality, life expectancy, literacy rate) in Costa Rica have improved along with ecological conservationFig. 56-24Life expectancyInfant mortality200150100500Infant mortality (per 1,000 live births)Year190019502000304050607080Life expectancy (years)The Future of the BiosphereOur lives differ greatly from early humans who hunted and gathered and painted on cave wallsFig. 56-25Detail of animals in a 36,000-year-old cave painting,Lascaux, France(a)A 30,000-year-old ivorycarving of a water bird,found in Germany(b)Biologist Carlos RiveraGonzales examining a tinytree frog in Peru(c)Fig. 56-25aDetail of animals in a 36,000-year-old cave painting, Lascaux, France(a)Fig. 56-25bA 30,000-year-old ivory carving of a water bird, found in Germany(b)Fig. 56-25cBiologist Carlos Rivera Gonzales examining a tiny tree frog in Peru(c)Our behavior reflects remnants of our ancestral attachment to nature and the diversity of life—the concept of biophiliaOur sense of connection to nature may motivate realignment of our environmental prioritiesFig. 56-UN1Genetic diversity: source of variations that enablepopulations to adapt to environmental changesSpecies diversity: important in maintaining structureof communities and food websEcosystem diversity: Provide life-sustaining servicessuch as nutrient cycling and waste decompositionFig. 56-UN2You should now be able to:Distinguish between conservation biology and restoration biologyList the three major threats to biodiversity and give an example of eachDefine and compare the small-population approach and the declining-population approachDistinguish between the total population size and the effective population sizeDescribe the conflicting demands that may accompany species conservationDefine biodiversity hot spots and explain why they are importantDefine zoned reserves and explain why they are importantExplain the importance of bioremediation and biological augmentation of ecosystem processes in restoration effortsDescribe the concept of sustainable developmentExplain the goals of the Sustainable Biosphere Initiative