Chapter 8: Conservation biology
Edited by Peter Moyle & Douglas Kelt
By Peter B. Moyle and Anitra Pawley, last revised September 2004
The field of Conservation Biology developed as it became more and apparent that we are facing a global extinction crisis (Chapter 4). Conservation Biology has multiple origins. It draws its focus on applied, habitat and ecosystem oriented solutions from fields such as wildlife management and forestry. It is based largely on theory from biology, especially ecology and population biology. It draws its energy from the environmental movement, from people concerned about the direct effects of environmental change on their own health and well being. It has a philosophical and spiritual foundation stemming from the world’s religions and from the ethical thinking of environmental philosophers. Increasingly, conservation biology also includes major components from the social sciences, recognizing that extinction trends will not be halted unless the major problems of humanity can also be solved through major changes in our social systems. Conservation biology is thus a integrative discipline that is focused on understanding how humans are changing the world and on finding practical solutions to saving biodiversity. It is based on the assumption that conservation of biodiversity will come from recognizing that humans are part of nature and not separate from it: it is in our own best interests to protect keep ecosystems, habitats, and species from extinction.
The following sections of this chapter give you some idea of the diversity of tools and approaches used by conservation biologists to protect biodiversity. Much more comprehensive discussions of tools and approaches can be found in recent texts in conservation biology.
MINIMUM VIABLE POPULATION SIZE: AN ANALYTICAL TOOL
Biologists have long realized that the smaller the population, the more susceptible it is to extinction. This is hardly surprising. But how small can a population be? Since the National Forest Management Act of 1976, the term minimum viable population size has come into wide use. This act required the U.S. Forest Service to maintain “viable populations” of all native vertebrate species in each National Forest. But what does this mean? How long are we protecting species for? A somewhat arbitrary definition proposed by Schaffer is that, “a minimum viable population for any given species in any given habitat is the smallest isolated population having a 99% chance of remaining extant for 1000 years despite the foreseeable effects of demographic, environmental, and genetic stochasticity and natural catastrophes.” In other words, it is the smallest number of a species that can maintain a population for the indefinite future. Determining a minimum viable population is not an easy task. Nor can the viability of populations be pegged to one magic number. Despite these problems, the approach is a useful concept to help prevent extinctions.
Ideally when determining a minimum viable population, a biologist must weigh the requirements of the individual species and the external factors that test the ability of a species to adapt. Factors that test the capabilities of a population to adapt include natural factors, including variation in demographic, environmental, and genetic factors, as well as natural catastrophes. The more frequent a population is exposed to these events, the more likely it is to become extinct. Human factors, ranging from urbanization to noise created by vehicles, are typically an additional stress on species which increasingly are pushing species that are naturally stressed towards extinction. Thus the combination of natural and human factors has caused to coho salmon populations to reach dangerously low levels in California streams. Natural factors included long-term droughts and major floods, which caused a reduction in potential habitats for juveniles in fresh water, and changes in ocean conditions, which reduced survival of adults in the ocean. Human factors included activities (such as logging and road building) that degraded freshwater habitats in a massive fashion and fishing in the ocean which reduced adult populations. California coho were listed as a threatened species by the National Marine Fisheries Service in 1997, recognizing that many populations of coho were already extinct and that others were at or below the minimum viable population size.
The role chance events play in the survival and reproductive success of a population is termed demographic stochasticity, a term which makes a good mantra when repeated over and over. What it means is that the smaller the population, the greater the probability that all or most of the offspring of the remaining females will not survive or will be of one sex or will not be able to find one another to mate. Variation of physical factors such as rainfall, and biological factors such as predation, competition, parasites, and diseases play an increasingly important role the smaller a population becomes. For example, the blackfooted ferret nearly became extinct when an epidemic of canine distemper (a disease ultimately contracted from domestic dogs) swept through the last population. Similarly, the endangered red cockaded woodpecker was decimated along the eastern Atlantic seaboard when Hurricane Hugo devastated much of its remaining forest habitat.
Genetic factors also play an important role in the survival of a species. The smaller a population, the greater the risk of the loss of genetic material because not all individuals reproduce. Smaller populations have fewer genes upon which evolution can act. With less genetic material, populations may lose their vigor, have reduced fertility, and become more susceptible to genetically related problems. Numerous examples of this have been documented in zoo populations. For example, in zoos a strain of white tigers bred from a few individuals is known for being cross-eyed and having abnormal hip joints. Just how small a population must be before such problems become irreversible varies among species.
Sometimes populations go through a natural crash in numbers and then recover, but without the genetic variability they once had. This is referred to as a genetic bottleneck because small populations are rarely completely representative of the original genetic composition of a population. Certain traits that are desirable in an evolutionary sense may be lost. When exposed to selective factors, populations that have gone through a bottleneck are less likely respond to selective pressure and more likely become extinct. The cheetah is the classic example. The cheetah occurs naturally in the African savannah in low densities, one per every forty or fifty square miles. Cheetahs have been found to have extremely low genetic variability, indicating that all cheetahs today are most likely descended from a very small population that experienced a genetic bottleneck. They are nevertheless a successful predator, although there is concern that their low genetic diversity may make them exceptionally vulnerable to epidemic diseases or make it difficult for them to adapt to major climatic changes.
Because the factors that affect minimum population size are often intertwined and inherently difficult to quantify, assessing the relative importance of each is at best guesswork. The heath hen, once common from New England to Virginia, was reduced to a population of 100 on Martha’s Vineyard island by 1900, as the result of human-caused habitat changes and hunting. A portion of the island was set aside as a refuge and, under management, the bird’s population increased to 800 in just sixteen years. However, within just a few years, a fire, predation by an unusually high number of goshawks, and disease took its toll. In 1920 the population was under 100, and 12 years later the last survivor of the population, which had a high percentage of sterile male individuals, died.
The direct determination of a minimum viable population size based on multiple factors has rarely been attempted. Experiments on extinction are for obvious reasons impossible to perform! Other direct attempts require large data sets and complicated computer models. Shaffer (1981) used a simulation approach for the grizzly bear in Yellowstone National Park. He found that grizzly bears survival was most affected by demographic and environmental affects. Mortality rate, cub sex ratio, and age at first reproduction most affected survival. More to the point, his results indicated that populations of less than 30-70 bears occupying less than 2500-7400 sq km have less than a 95% chance of surviving for even 100 years!
CAPTIVE BREEDING PROGRAMS: A DESPERATION APPROACH
When a species has reached numbers close to what biologists judge is the minimum viable population size, captive breeding programs may be initiated, at least for large vertebrates. The breeding of wild animals in zoos is practiced for many purposes, but recently the focus has been on breeding endangered species with the intent of reintroduction in the wild. Though most conservationists abhor the thought of placing animals in zoos or game parks, it is generally thought preferable to the total annihilation of a species. However, zoos, until fairly recently, were seen as places that used animals mainly for display before the curious public, that abused animals through neglect or bad living conditions, and that had little redeeming value as conservation tools. In addition, Captive Breeding Programs were scarce and often miserably unsuccessful. In 1972, Perry et al. found of the 162 rare or endangered mammal species in U.S. zoos, 73 had been bred and only about 30 had met with sufficient success to provide any hope of their reintroduction in the wild.
More recently zoos and game parks have been receiving attention for their successes in Captive Propagation (CP) as well as their role in educating the public in conservation. The Arabian Oryx, a small, almost pure white antelope with long, nearly straight horns, was known from biblical times to exist in the Near East. Killing an oryx, known for its endurance and strength, was considered a sign of manhood in this area. This practice did not deplete oryx populations severely when men killed oryxes by throwing spears or shooting antique rifles from camels, but the introduction of automobiles and automatic weapons led to the oryx’s annihilation in the wild. Fortunately, the oryx existed in zoos–there were sixty-four in three U.S. zoos in 1979. Oryx have been reintroduced into the Middle East and, with Bedouin guards (the people who were partly responsible for their demise), their populations appear to be doing quite well. Other successful reintroductions include the return of European bison in Poland, the black buck in Asia, and wolves in Bavaria. But too often success is claimed upon only the first step, successful breeding in captivity. If the recently reintroduced Arabian oryx never learn their wild ancestor’s trick of migrating to seasonal waterholes, have we really saved the species? This is the type of question posed by critics who oppose CP due to genetic, ecological, and behavioral considerations. Consider, for example, the Ashkania Nova Zoo herd of eland, which suffers from a high level of disease due to inbreeding. Or, consider the more recent attempts to breed Europe’s vanishing storks. Most of the storks raised in captivity and released into the wild do not migrate to Africa as the naturally raised individuals do. To insure their survival, the storks must be fed during the winter. In some cases captive-reared storks are displacing some of the few remaining wild pairs. This example raises a deeper philosophical question: when a species is approaching extinction, how much change in its genetic or behavioral traits are we willing to tolerate in order to save it? Frequently, if captive breeding is “successful,” the species can be maintained only in an artificial environment. It is far easier to select for traits that are adaptive in captivity than maintain a semblance of the original wild species.
This phenomenon and a feeling for the intrinsic right of animals to remain “free,” had led some conservationists to object to CP on any grounds. There are also those who object to the practice for fear that CP efforts will remove the impetus to preserve natural habitats. And others point out that the decision to conserve a rare animal is a decision to sacrifice a significant number of the few remaining wild specimens to a program that may fail. The California condor is a perfect example of the controversy surrounding CP. This scavenger, with a wingspan of over nine feet, had a wide range, from Florida to Texas and Northeastern Mexico, northward west of the Rockies to British Columbia. By the 1960s the breeding range of the condor had contracted to Southern California and a population of only fifty condors survived. Just 20 years later, less than half the species survived. It appeared that extinction was imminent without intervention by man. This led a group of experts chosen by the National Audubon Society and the American Ornithologists’ Union to propose a “hands on” approach to save the wild condor. The U.S. Fish and Wildlife carried out the plan, which included an extensive survey of condor biology through capture and radio tagging. Later it was deemed necessary to begin a captive breeding program. Because of the success in another similar species, it was felt that birds in captivity could be induced to lay more eggs and survive better than in the wild where they were plagued by illegal shooting, pesticides, limited habitat, and prey availability. This proposal was protested by many conservationists, including members of the Sierra Club and the Audubon Society who originally supported the study. The risks in handling and in rearing a species that was no longer equipped for a wild existence, and the loss of an impetus to protect the condor’s native habitat were cited as reasons for their opposition. Kenneth Brower, a nature writer put it in a simpler, albeit poetic, fashion:
“And what if nothing can bring the birds back? What if Gymnogyps, watching Los Angeles sprawl towards its last hills, has simply decided it is time to go? Perhaps feeding on ground squirrels, for a bird that once fed on mastodons, is too steep a fall from glory. If it is time for the condor to follow Teratornis, it should go unburdened by radio transmitters.”
Yet the breeding of California condors in captivity has been a success and the release of captive-reared birds in the wild is now being done. Some of the released birds have died from causes as diverse as consuming antifreeze to being killed by a golden eagle defending its territory. Others have survived, however, and a particularly promising event has been the release of birds in remote canyon country in Arizona, from which they have been absent in historic times.
Figure 8.1 California condor in captivity. Photo © State of California.
Many criticize captive breeding efforts for their choices in species. Nearly all the species are large, dramatic species like lions, rhinos, and birds of prey. Yet these very animals are slow breeders and costly to maintain in captivity. There are few programs for insects or rodents! Zoos are beginning to establish priorities for CP and coordinate their efforts. Coordination and trading of animals is particularly important to prevent genetic problems caused by inbreeding. Aside from considering the ecological and scientific importance of the species, CP efforts should be chosen with practical matters such as cost and potential reintroduction success. Despite the success of some CP efforts, and even with increased success, CP can never really be a panacea to extinction. This leads us to consider another means of saving species: protecting the habitats in which they live.
RESERVE DESIGN: SETTING ASIDE AREAS TO PREVENT EXTINCTION
Habitat destruction is a major cause of extinction. However, if we are to maintain certain habitats, we must consider the requirements of all species within the ecosystems we are attempting to protect. For example, in determining the boundaries of a nature reserve, we can’t overlook the geographic ranges of the species within the reserve. Yellowstone National Park, for example, is large enough to preserve viable populations of butterflies and bison, but not of grizzly bears. The salmon that spawn in a large river flowing through a part are not protected if their migration is blocked by a dam below the park or if the headwaters of the river are outside the park and are logged, resulting in erosion and the smothering of eggs with silt from the land.
In a nutshell, if a variety of species are to persist, a variety of habitats must also persist. Nature reserves should be chosen in a coordinated fashion. Ideally, the international community should coordinate its efforts to choose nature reserves that, when considered jointly, represent the widest range of species possible. For example, Kirkland’s warbler nests only in Michigan and winters only in the Bahamas. Preserves in both places are needed to protect the species. Though the ecology of species should be our prime consideration, political and financial realism must also play a role. It does little good to protect a species without the support of those individuals which are most likely to gain from its direct or indirect demise. In the following discussion, we will investigate the biological constraints of reserve design as well as some of the political and economic considerations.
What exactly is a reserve? Reserves come in all shapes, sizes, and are established for various purposes. Some are areas where human use is strictly limited, often called preserves. Others permit various levels of human use. Partial reserves are fully protected during the breeding season of selected organisms (e.g., some beaches are closed during the breeding season of the least tern; the rest of the year they are open for recreation). Extractive reserves allow the extraction of resources in a carefully managed way to insure the maintenance of the reserve ecosystem to the benefit of the individuals who use it for their livelihood. Chico Mendez, a famous Brazilian “seguiero” (rubber tapper), brought this type of system to the limelight in his quest for the protection of Amazon forests for the extraction of rubber and other products from wild trees. It has become increasing apparent that large expanses of land relatively free from human pressures are difficult to find. In fact, on close examination, they are non-existent, even in remote places like the Antarctic. Recently, environmentalists have discovered that the establishment of extractive reserves may be a compromise that allows humans and nature to coexist as they have in some areas for centuries. What ever type of reserve is established, it must be part of a broader system of protected areas and it must be actively managed. The big question always seems to be: given limited financial resources, what is the best way to develop a system of protected areas?
THE RESERVE CONTROVERSY: NUMEROUS SMALL OR FEW LARGE ONES?
Traditionally, particularly in the U.S.A., we have sought to preserve large tracts of wilderness as nature reserves. However, some investigators have questioned whether this is always the most appropriate strategy. Perhaps a series of small reserves, spread across the landscape and representing a wider variety of habitats would be better. If we have to decide between a large number of small reserves or a few large ones, what is the best strategy for maintaining species diversity?
One approach to answering this question has been through the study of Island Biogeography. Nature reserves are like islands in a sea of modified habitat. Thus the trend has been to study islands in the hope that they can provide an understanding of what habitat fragmentation will mean to species survival. The theory predicts that over time, islands that have become separated from continents reach a dynamic equilibrium in the number of species. The forces that bring about this equilibrium are immigration of new species and extinction of old ones. This equilibrium depends mostly on the island’s size and distance from the continent. Once an area is isolated from its source of immigrant species, the patch undergoes a reduction of species as immigration and extinction rates balance one another. Immigration rates decline causing species diversity to decline, which results in reduced extinction rates due to decreased competition.
However, this theory, despite its merit, is not very good at predicting the speed of species loss. Yet logic indicates that large “islands” with larger species populations and the possibility for greater genetic variability would tend to lose species at a slower rate than would smaller islands. Recent studies indicate that this is indeed the case. Studies of land bridge islands (islands that were attached to land before the recent interglacial period began about 14,000 years ago) have supported this view as have studies of small mammal faunas that were isolated on mountain ranges rising out of the Great Basin Desert in California, Utah, and Nevada. These mammal faunas were contiguous during the cooler glacial climates which existed prior to 10,000 years ago. As temperatures rose, the populations and associate woodlands retreated to the tops of the mountain ranges. The analysis of these isolated groups has shown that the bigger the mountain top, the more species will be present.
Figure 8.2. Jepson Prairie is a reserve near Dixon, California, that illustrates may of the problems with protecting natural areas. Roads and powerlines run through it and fences reflect its history as a ranch used for grazing sheep. It is a relatively small island of habitat, yet it contains endemic and endangered plants and animals, as well as spectacular wild flower displays in spring. Most of the year, however, its vernal pools and grasslands are dry, brown, and dusty. Photos by P. Moyle.
Such studies indicate that reserves must be very large to limit the number of extinctions. In fact, even the largest reserves that exist today are probably not large enough. Soulé et al. (1979) predicted that large nature reserves (>10,000 sq km) will loose over half their species in 5000 years. However, if immigration rates to reserves can be increased by their proximity to other reserves, extinction rates will also decline. This has led many conservation biologists to propose that nature reserves should be as large and as close together as possible or connected by conservation corridors. These corridors would allow species to disperse between reserves, increasing the probability of their survival even in the face of disturbance. An alternate point of view has been that a series of small reserves would preserve more species diversity than a large reserve of equivalent area because different sets of species would survive in different reserves. Reserve sites could be chosen to protect specific ecosystems, such as a deep canyon or small lake. In addition, the species in a series of smaller reserves would be less likely to be completely annihilated by a calamity such as a fire, storm, or disease because species would be found in more than one location (provided habitat types were found in more than one reserve).
As you can see, reserve size, number, and proximity are complicated questions that are not easily answered. Ecological and behavioral studies are necessary if we are to make informed decisions on reserve design. The answers are probably mixed depending on the type of habitat and species we wish to protect. As mentioned above, some species require huge ranges; others require limited ranges. Yet as the concerns of various conservationists are evaluated, there is an emerging consensus: We should seek to have as much area protected as possible, a few large preserves to protect the species that require large ranges and many small specialized preserves that will maintain the unique species within them. Establishing more small protected areas in a variety of habitats may save more species than establishing fewer large preserves of equal area. For example, the total number of mammals protected in three different habitats (Redwood, North Cascades, and Big Bend National Parks) exceeds the number in the single largest North American park. We have also begun to realize that even our biggest parks, like Yellowstone National Park, are not big enough. Thus a major proposal is being discussed today to protect the Greater Yellowstone Ecosystem, an immense area surrounding the part that is intimately tied to it through ecosystem processes such as animal migrations. The Greater Yellowstone Ecosystem includes many private and public lands, including towns and ranches. Thus maintaining this ecosystem requires close cooperation between the region’s human inhabitants and ecosystem managers. The difficulty of achieving such cooperation is demonstrated by the slaughter, in the winter of 1996-97, of a majority of the Park’s bison, which were migrating out of the park, in order to protect regional cattle herds from the largely hypothetical threat of contracting a disease, Brucellosis, from the bison.
Although more research is always needed to make the best decisions, the urgency of the extinction problem implores us to make decisions now. Politics and economics may not always enable us the luxury to consider all issues when designing reserves, but ecology and biology must influence reserve design whenever possible.
WATERSHEDS: LANDSCAPE PROTECTION
Most discussions of preserves have focused on big blocks of land or on regions defined by plant communities, especially trees and shrubs (e.g., coastal sage scrub, redwood forest). Flowing through these blocks of land, however, are streams and rivers. The streams may have their headwaters upstream of the protected area and their mouths far downstream from the protected area. Thus a logging operation in the headwaters may cause a major landslide from which sediment may be carried many miles downstream into the protected area. A dam just downstream of the protected area may prevent migratory fish, such as salmon, from reaching their historic spawning grounds. An upstream pesticide spill may kill fish far into the preserve. A non-native species planted in a downstream reach may invade and become abundant in the preserve. Not surprisingly, many parks and preserves have beautiful forests or prairies with large populations of native mammals and birds, but streams that are degraded, containing non-native species. For example, The Nature Conservancy has a beautiful preserve along the McCloud River in northern California that contains old-growth trees and a high diversity of terrestrial plants and animals. Yet the river is missing some of its most important inhabitants. Chinook salmon and steelhead, once present in large numbers, are now denied access by Shasta Dam downstream. Bull trout, once an important predator on juvenile salmon, are now extinct. Brown trout, an exotic species, however, are common. Thus, this preserve has to be regarded as having lost significant biodiversity. It is likely that more has been lost from the McCloud region than we realize, because the salmon were once a major source of food for bears and other predators, which would carry the nutrients represented by the salmon into the surrounding forests.
The fact that traditional parks and preserves often do not protect aquatic environments adequately is reflected in the growing realization that aquatic species and ecosystems are often the most endangered ecosystems in a region. A recent (1996) evaluation of the status of species and ecosystems in the Sierra Nevada in California, showed that aquatic systems were in the most trouble, with a number of species of frogs, fish, and aquatic invertebrates in danger of extinction. The best way to reverse this trend to protect entire watersheds. Watersheds are the entire drainage basin of a given stream or river, from ridgetop to mouth. Because river systems are made up of small trickles feeding into brooks feeding into bigger streams feeding into rivers, watershed are nested within one another.
For example, unnamed tributaries flow into Cub Creek (a steep trout stream), which flows into Deer Creek (a salmon spawning stream), which flows into the Sacramento River. Each has a progressively larger watershed which are increasingly difficult to protect as size increases. Cub Creek and its tributaries are completely protected from logging and other insults as a US Forest Service Research Natural Area. Deer Creek flows through the Ishi Wilderness Area and parts of Lassen National Forest and is of great interest for protection because it contains one of the last populations of wild spring-run chinook salmon. Yet about half of its watershed is owned by ranchers, timber companies, and small landowners. Protection of the watershed is being accomplished by a coalition of landowners (Deer Creek Watershed Conservancy) working with state and federal agencies. The general framework for protection is that (1) private landowners must be allowed to continue to make a living from their land, (2) the national forest lands should be operated for overall public benefit, including extractive uses, (3) the key natural elements, such as chinook salmon, must be protected and enhanced, and (4) actions taken in one part of the watershed are likely to affect all other parts of the watershed. This framework indicates that the Deer Creek watershed is not a preserve in the traditional sense, but an ecosystem that includes humans as active players in it.
Figure 8.3. Deer Creek, Tehama County, California is one of the last refuges of the threatened spring-run Chinook salmon, which have been protected by its rugged canyons, difficult to access. A major conservation challenge is that much of the watershed is privately owned (blue is Lassen National Forest, green is the Ishi Wilderness Area, the rest is private). Photos by P. Moyle, map by G. Sato.
Deer Creek flows into the Sacramento River, the largest and perhaps most modified river in California. Since it provides much of the water for central and southern California human activities, this river has been extensively dammed and diverted, channelized, polluted and otherwise degraded. Yet there is growing realization that even in this system, the entire watershed must ultimately be managed in an integrated fashion, especially if the remaining natural elements (such as the chinook salmon that must pass through the river to reach Deer Creek) are to be protected. A watershed management strategy may ultimately benefit the human inhabitants of the region as well, by providing a cleaner and more reliable water supply, by providing increased protection from floods, and by increasing the aesthetic and recreational values of the river and its tributaries.
The growing interest in watershed management results from the realization that (1) we all live in watersheds and (2) watersheds are a natural unit on the landscape, typically easy to define even if they cross political boundaries. In the USA, citizen watershed groups are springing up like mushrooms after a rain because people are increasingly understanding the enormous benefits to be gained from holistic watershed management. One of those benefits is better protection of aquatic and riparian ecosystems and their associated native biota.
CHOICES: WHAT SHOULD WE PROTECT?
Each species is a unique and separate natural entity that, once lost, can never be revived. The ideal would be to save all species, even every local population of species. Yet this is obviously not a viable option. When protecting species and establishing reserves, we are faced with difficult choices. Which species do we protect? Which habitats are most critical? How do we make these decisions in light of the stresses that overpopulation and human lifestyles place on these systems?
The controversy over the Mount Graham Red Squirrel illustrates the decisions we are faced with. The University of Arizona, with the backing of an international consortium of astronomers, wishes to build a complex of telescopes atop Mount Graham in southeastern Arizona. This same area is the heart of the range for the Mount Graham red squirrel, a distinct subspecies that is found nowhere else and forms the southernmost population of the entire species. It is feared that this project will decimate the habitat of the last 100 surviving squirrels. What is a measly subpopulation of squirrels compared to a project of this magnitude and human significance? Gould (1990) illuminates the real issue at stake. The answer may lie not in the species but in the habitat itself. The Pinaleno Mountains, reaching 10,720 feet at Mount Graham, are an isolated fault block range containing unique old-growth spruce-fir habitat. The squirrel is able to exist in this southerly location because of the high elevation. In addition, these elevated bits of old growth habitat represent “sky-islands” which were isolated 10,000 years ago after the last Ice Age. Islands like these are powerful tools to those who wish to study evolutionary theory and being remnants of the past are precious habitats that probably should not be compromised.
So when considering which areas to conserve, we must weigh every aspect. Biologists tend to think of protecting species for their intrinsic appeal, but in a practical world where politics and economics often play a more important role than aesthetics, it is necessary to measure the utility of species as well as habitats. Decisions must be based on a mixture of historical, evolutionary, community, and species approaches blended with a strong dose of reality. A recent World Resources Institute publication (Reid and Miller, 1989) recommended the following three rules of thumb to evaluate the trade-offs and value judgments made in setting priorities for protecting biodiversity:
1) Distinctiveness. Numbers aren’t everything. Preserving an entire species is clearly more important than saving populations of those with numerous representatives.
2) Utility. Global or local, current or future? When evaluating what to save, we clearly have to evaluate utility, often from opposing perspectives. For example, to humanity at large, tropical rainforests are extremely important not only because they contain a variety of life, but because they influence global climate.
3) Threat. Saving the most beleaguered species and ecosystems first. When establishing priorities, it is probably most important to focus on those areas that are most at risk. For example, Central America’s tropical rain forests are less threatened than the remaining fragments of tropical dry forest in that region, indicating that our efforts should focus on the latter.
Alternately, a triage system can be established, in which the fewest resources are put into saving (1) species and ecosystems for which the extinction is likely no matter what we do and (2) species and ecosystems that may be in decline but for which long-term persistence is likely. The most resources are therefore put into the middle category, species and ecosystems in which an infusion of energy and funds is likely to make the biggest difference in terms of conservation. The reality, of course, is that most protection decisions are made on a political basis. An example of a widespread ecosystem may be protected because it is near a large city and is familiar to local people, while a rare habitat that is easy to protect may be ignored because it is in a remote part of a distant continent. For this reason, we need global strategies with global funding, focusing on working with local peoples on integrated strategies for conservation, such as watershed conservation strategies.
Although conservation efforts tend to focus on protecting relatively undisturbed areas as reserves or on restoring damaged areas to a more naturally functioning state, the amount of land and number of species likely to be protected in this way is relatively small. Michael Rosenzweig of the University of Arizona, therefore, has proposed development of reconciliation ecology (Rosenzweig 2002). The basic idea is that protecting biodiversity will require incorporating the wildlife we treasure into human dominated systems. There are many species that can thrive in such systems if we provide them with what they need to complete their life cycles successfully. For songbirds, including tropical migrants, for example, this may mean incorporating appropriate trees and bushes for nesting and feeding into urban landscapes, in patches that the birds can use (and also excluding artificial predators such as cats).
Sometimes reconciled landscapes can be on a large scale. For example, separating Davis and Sacramento is the 24,000 ha Yolo Bypass, a wide, shallow channel which was designed to bypass flood waters around Sacramento. Built in 1920s and 30s, the Bypass has been enormously successful in protecting Sacramento at relatively low cost. While historically the main use of bypass lands has been for agriculture, recent studies have demonstrated that it is very important for fish and wildlife. When it floods, huge flocks of ducks and geese forage in its productive waters. Juvenile salmon that enter the flooded areas grow faster than their compatriots that stay in the main river; when they leave the Bypass, they are larger than river-reared salmon and so presumably survive better when they go out to sea. Sacramento splittail, a large native fish that requires floodplains for spawning, depends on the Yolo Bypass for spawning and rearing of its young. Recognition of these values has resulted in the enhancement of parts of the Bypass as wildlife refuges, while other parts are maintained in productive agriculture. Interestingly, the Yolo Causeway, the highway bridge that crosses the Bypass, supports the largest colony of bats in California. These bats have found a great place to roost in the middle of a region swarming with the insects they eat. The Yolo Bypass is a good illustration of how, with imagination, human created landscapes can contribute to the protection of biodiversity (Sommer et al. 2001).
Figure 8.4. Top. Yolo Bypass in full flood with Sacramento in the background. Bottom. Same view in autumn, across the Yolo Basin Wildlife Area.
Conservation biologists face the ultimate problem in conservation: the rates of extinction far surpass those of the most apocalyptic mass extinctions our planet has ever experienced (Ward 2004). Under human domination, our planet is becoming a biologically impoverished image of the world that supported humanity in past generations. Already we can no longer thrill to the sight of waves of migrating passenger pigeons, hoards of bison, and the splashing of salmon in many rivers. We are a powerful biological entity. We are making choices that will influence humanity for centuries to come, not to mention the Earth’s biota, even after we have gone. In fifty million years, we may not exist. What does exist will largely be a result of the action we take today. We are the problem; can we be part of the solution, using tools such as those discussed in this chapter? Conservation Biology is a discipline that is attempting to find ways to make humanity more compatible with wildlife and wild ecosystems, using the best available science. It is a crisis discipline that is under-funded and under-appreciated. This is because its practitioners are mainly advisors and the real solutions are political. As the USA’s failure to ratify the Kyoto Accord dramatically demonstrates, we are a long way from finding political solutions to the problems of world conservation.
Meffe, G. K. and C. R. Carroll. 1997. Principles of Conservation Biology. 2nd Edition. Sinauer, Sunderland MA.
Moyle, P. B. and G. M. Sato. 1991. On the design of preserves to protect native fishes. Pp. 155-169. In W. L. Minckley and J. E. Deacon (Editors), Battle Against Extinction: Native Fish Management in the American West. University of Arizona Press.
Moyle, P. B. and R. A. Leidy. 1992. Loss of biodiversity in aquatic ecosystems: Evidence from fish faunas. Pp. 128-169. In P. L. Fiedler and S. A. Jain (Editors), Conservation Biology: The Theory and Practice of Nature Conservation, Preservation, and Management. Chapman and Hall, New York.
Moyle, P. B. and R. M. Yoshiyama. 1994. Protection of aquatic biodiversity in California: a five-tiered approach. Fisheries 19 (2):6-18 Myers, N. 1981. The sinking ark, A new look at the problem of disappearing species.
Raup, D. M. 1979. Size of the Permo-Triassic bottleneck and its evolutionary implications. Science 206:217-218. Raup, D. M. 1984. Death of species. In: Extinctions (M. H. Nitecki, ed). The University of Chicago Press, Chicago.
Reid, W. V. and K. R. Miller. 1989. Keeping options alive: The scientific basis for conserving biodiversity. World Resources Institute Report.
Rosenzweig, M. 2002. Win-win ecology. Oxford Univ. Press, Oxford.
Shaffer, M. L. 1981. Minimum population sizes for species conservation. BioScience 31: 131-134.
Simberloff, D. S. and L. G. Abele. 1976. Island biogeography theory and conservation practice. Science 154:285-286.
Sommer, T. et al. 2001. California’s Yolo Bypass: evidence that flood control can be compatible with fisheries, wetlands, and agriculture. Fisheres 26(8): 6-16.
Soulé, M. E., Wilcox, B. A. and Holtby, C. 1979. Benign neglect: A model of faunal collapse in the game reserves of East Africa. Biol. Conserv. 15:259-272.
Ward, P. 2004. The father of all extinctions. Conservation in Practice 5(3):12-19.