Chapter 25: Extinction and Conservation

Chapter 25: Extinction and Conservation Robert E. Ricklefs The Economy of Nature, Fifth Edition

Human Impact on Earth • The human impact on the earth is substantial: • in the year 2000, human population was 6 billion: • we are still growing at the robust rate of 2% per year • humans control or indirectly affect much of the earth’s surface: • 35% of land area is used for crops or permanent pastures • countless additional hectares are grazed by livestock • tropical forests are being felled at 17 million hectares per year • 2% of remaining forest is cut per year • desertification is a widespread problem, especially in Africa • air and water pollution are also widespread

Human impacts on the planet can be reduced. • Negative consequences of human impacts on natural systems are enormous: • deterioration of the environment: • will lead to a declining quality of life for all humans • already affects the other life forms on the planet • But there is cause for hope: • humans can live in a clean and sustaining world, but only by placing support for our own population into balance with preservation of other species and the ecological processes that nurture us

Three Lessons from Ecology 1 • The science of ecology has much to tell us about living sustainably in a healthy world. • Environmental problems cannot be solved until the human population is brought under control: • density-dependent control of the human population will mean untold suffering • we must learn to value individual human experience over numbers of progeny

Three Lessons from Ecology 2 • Individual consumption of energy, resources, and food produced at higher trophic levels must be reduced: • we have already exceeded the capacity of earth to support the current human population at a level enjoyed by the most affluent societies • we can make contributions to sustainability by: • investing in and utilizing energy- and resource- efficient technologies • eating lower on the food chain

Three Lessons from Ecology 3 • Ecosystems should be maintained in as close to their natural state as possible to keep natural processes intact: • areas unsuitable for grazing or agriculture should not be converted to such uses: • these areas are best set aside for conservation and recreation • living with nature is always preferable to, and less costly than, going against it

Biological diversity is incompletely described. • There may be as many as 10 to 30 million species of plants, animals, and microbes worldwide: • only 1,500,000 species have been catalogued • although lists are important, they represent only one approach to the documentation of biological diversity or biodiversity, the many unique attributes of living things

Components of Biodiversity 1 • Ecological diversity: • each species has unique attributes and adaptations that define its place in the ecosystem: • plants, for example, vary in: • tolerances of environmental conditions • defenses against herbivores • growth form • strategies for pollination and seed dispersal

Components of Biodiversity 2 • Genetic diversity: • crucial to evolutionary responses of organisms to changing environments • has both within- and between-species components • Geographic diversity: • each region has different species composition and diversity • endemic species are restricted to small geographic areas • regions with many endemics possess high endemism

Endemism • Oceanic islands are well known for harboring endemic forms: • nearly all native birds, plants, and insects of isolated islands live nowhere else • loss of such island species caused by habitat destruction, hunting, or alien species means worldwide extinction • humans have caused many extinctions of island endemics

Value of Biodiversity • Current loss of species is at an all-time high in earth’s history: • some estimates place this rate in excess of one species per day • Why should we be concerned about loss of species? • many species are gone already • extinction is a natural process

Moral Responsibility • Extinction raises important moral issues: • some feel that because humankind affects all of nature, it is our moral responsibility to protect nature • if morality is intrinsic to life itself: • rights of nonhuman individuals and species are as legitimate as the rights of individuals in human society

Economic Benefits • Individual species have direct economic and recreation values for humankind: • food resources • game species • sources of forest and other natural products • drugs and other organic chemicals • about 25% of prescriptions filled in the United States are extracted directly from flowering plants

Economic values of species can cause environmental harm. • Policies favoring certain species may harm others: • cultivated species displace other species viewed as having lesser value • predators, such as wolves, are eliminated because of conflicts with livestock operations • overexploitation of resources (such as fisheries) may lead to their demise

Ecotourism • Some species have high value because they attract tourists, in a practice known as ecotourism: • many countries have benefited from the willingness of tourists to visit game parks and preserves; ecotourism: • often brings much-needed foreign currencies into developing countries • is responsible for development of parks and preserves • is expanding, but its potential is finite: • people have limited resources to devote to such activities • many species and ecosystems are not attractive to ecotourists

Indication of Environmental Quality • Individual species may have value as indicators of environmental change: • birds of prey declined during the 1950s and 1960s in the United States: • this decline was traced to pollution of aquatic habitats by breakdown products of DDT, which: • entered aquatic food chains and were concentrated at each step in the chain • interfered with physiology and reproduction in birds • identification of the problem led to banning of DDT and subsequent recovery of many species

Maintenance of Ecosystem Function • Diversity may help stabilize ecological systems: • the research of Tilman and Downing has shown that biomass production was less affected by drought on high-diversity plots: • with many species present, some can assume key roles when environmental conditions change • such switching is less likely in less diverse systems

Extinction is natural, but its present rate is not. • Extinction is of concern because evolutionary lineages are lost forever. • The relatively low rate of natural extinction is called background extinction: • life span of most species in the fossil record is 1 to 10 million years • analysis of the fossil record indicates a background extinction rate of 1 species per year

Other Types of Extinction • Mass extinctions are caused by natural catastrophes, such as meteor impacts: • such bolide impacts are thought to occur at intervals of 10 to 100 million years: • may have been responsible for mass extinctions at the end of the Paleozoic and Mesozoic eras • Anthropogenic extinctions are caused by humans: • such preventable extinctions have brought the modern extinction rate to far in excess of natural levels

Humans cause extinctions by several mechanisms. • Populations disappear because deaths exceed births over a prolonged period: • extinction may be viewed as a failure to adapt to changing conditions • a recent survey has revealed the principal causes of population decline for endangered U.S. species: • habitat reduction and modification (67% of cases) • small population size • introduction of exotic species • overexploitation

Habitat Reduction and Fragmentation • Habitat reduction and fragmentation threaten many species: • some habitats are reduced or eliminated altogether • fragmentation creates a suite of additional problems: • small areas may not be able to support viable populations of larger species, such as mammals • small populations are subject to stochastic local extinction • fragmentation increases edges, exposing forest interior species to increased parasitism and predation • species of fragmented habitats may be unable to migrate with changing climate induced by global warming

Small Population Size • Stochastic extinction is a risk that increases dramatically for the smallest populations. • Reduced genetic variation in small populations may further increase the probability of extinction: • founder effects, inbreeding, genetic drift, and population bottlenecks all pose problems • some species, notably the northern elephant seal, have survived severe population bottlenecks successfully

Introductions of Exotic Species • Decreases in habitat quality are frequently the consequence of introduced predators, competitors, or disease organisms: • many species arrive accidentally and others are introduced intentionally • islands seem to be most vulnerable to introduced species (Hawaiian Islands have suffered greatly from introduced species) • aquatic systems are also vulnerable to effects of exotics • continental areas are not immune to effects of exotics

Overexploitation • Many species have succumbed to effects of direct exploitation by humans: • efficient hunting and fishing may drive species to extinction • humans have a long history of overexploitation: • arrival of humans in North America was accompanied by rapid extinction of 56 species in 27 genera of large mammals

Vulnerability to extinction is poorly understood. • Why some species are more vulnerable to extinction than others is hard to determine. • Some attributes that predispose species to extinction include: • species attractive for exploitation • species that have evolved in the absence of hunting • species that have evolved in the absence of diverse disease organisms • species with limited geographic range, restricted habitat distribution, and small local population size

Conservation Planning • Successful planning for conservation must include adequate habitat for a self-sustaining population: • in practice, conservation planning must consider: • ecological requirements of the species • amount of space needed to support a minimum viable population

Minimum Viable Populations • The minimum viable population (MVP) is the smallest population that can sustain itself in the face of environmental variation. • MVPs must be large enough to remain out of danger from stochastic extinction. • Other minimal attributes include: • wide distribution, such that local catastrophes cannot affect the entire species • some degree of population subdivision that can prevent the spread of disease

More on Conservation Planning • Migrations complicate conservation planning: • seasonal movements or different seasonal habitat needs are difficult to satisfy: • the entire Serengeti ecosystem of East Africa is needed to accommodate seasonal movements of wildlife • long-distance migrants may face multiple challenges in breeding and wintering grounds • It is not feasible to plan for the conservation of every species: • focus is increasingly on habitat conservation

Critical Areas for Conservation • What are the most valuable areas for conservation of species? • the focus is on areas serving as havens for the largest numbers of species not represented elsewhere: • such biodiversity hotspots typically combine local diversity and endemism • in continental areas, the objective is to target habitats and areas of special biological interest: • several small preserves may be more effective than one large preserve • adding more area to preserves becomes increasingly expensive

Challenges of Tropical Conservation 1 • Many tropical countries have large tracts of uncut forest and other undisturbed tropical habitats: • it may be relatively easy to set aside parks “on paper,” but many conflicts remain: • rapid growth of human populations • increased exploitation of forest products • illegal or questionable activities of poachers, squatters, miners, and logging concessions

Challenges of Tropical Conservation 2 • The price of conservation is rising worldwide. • Conservation must be an international effort, with wealth of the developed countries shared globally to protect biodiversity: • involving local people in the design and management of parks is especially important: • the benefits of conservation must be tangible and economically compelling

Design of Nature Preserves 1 • Ecological principles derived from the theory of island biogeography can be helpful: • the species-area relationship: • larger areas support more species than smaller by: • reducing likelihood of stochastic extinction • promoting genetic diversity • buffering populations against disturbances • the avoidance of edge effects: • the effects of habitat alteration extend for some distance • freedom to migrate

Design of Nature Preserves 2 • General recommendations exist for creation of preserves from large expanses of uniform habitat: • larger is better than smaller • one large area is better than several smaller that add to the same size • corridors connecting isolated areas are desirable • circular areas are better than elongate areas with more edge

Design of Nature Preserves 3 • Several small areas in different habitats may be more effective than one large area in uniform habitat. • Nature preserves must be designed with the habitat requirements of their inhabitants in mind: • migratory needs must be accommodated through incorporation of diverse habitats linked by corridors • roads and pipelines interfering with movements must be bridged in some fashion

Endangered species have been rescued from the brink. • The California condor is a success story with several important lessons: • the condor population had dwindled to less than 20 individuals in the 1980s • the decision was made to bring the entire population into a captive breeding program • this program has been very successful, highlighting the important role played by zoological parks • the condor can now be released into habitat preserves purchased expressly for condor conservation

California Condor • Experienced gained through projects like that designed for the California condor will have many benefits: • experience gained will benefit similar programs in the future • large tracts of natural habitat have been preserved • such projects heighten the public’s awareness of conservation issues: • condor populations are compatible with other land uses (recreation, hunting, ranching), so long as appropriate precautions are taken

Condor Conservation • Concessions to condors are neither difficult nor expensive. Making them simply depends on instilling values that acknowledge natural systems as an integral part of the environment of humankind.

Summary 1 • Humankind has an enormous impact on earth and its natural resources. These impacts will continue to grow as the population grows beyond 6 billion. • Resolving the environmental crisis will require cessation of population growth, conservation of energy and resources, and taking ecological values into consideration. • Biodiversity has ecological, genetic, and geographic components.

Summary 2 • The value of species is rooted in moral, aesthetic, and economic considerations. Species also have value as indicators of environmental quality. Diversity may also help stabilize ecosystem function. • Background extinction may be estimated from the fossil record. Mass extinctions are associated with catastrophic events, while anthropogenic extinction has increased dramatically.

Summary 3 • Habitat reduction may hasten a population’s decline toward extinction. Introduction of exotic species is also a substantial cause of extinctions. • Optimal design of nature preserves takes advantage of biodiversity hotspots, and principles elucidated in the theory of island biogeography. • Species may be brought back from the brink of extinction. Such efforts highlight conservation problems and may also conserve natural habitats.

Chapter 25: Extinction and Conservation