Conservation

We are living in an era of unprecedented loss in biodiversity. The most optimistic projections forecast the loss of several thousand species over the next few decades; less sanguine conservationists fear that almost a million species may vanish before the end of the present century. The earth has suffered mass extinctions before, but the present episode is qualitatively different for two reasons: first, it is extremely rapid; second, it is caused by one mammalian species, a large, primate of African origin. Ironically this creature has named itself Homo sapiens, the Wise or Knowing Man.

The human activities that threaten wildlife and ecosystems worldwide include deforestation, pollution, over-exploitation of native species, introduction of non-native species, acceleration of climatic changes, and spread of infectious diseases. The essential problem is that more and more people are using more and more resources, leaving less and less for other animal species.

Threats to biodiversity

For more than 99% of its species history, H. sapiens existed in small groups of hunter-gathers, a highly intelligent primate that learned to exploit virtually every terrestrial environment that existed on Earth. About 8,000–12,000 years ago, however, people largely ceased living within the constraints of given ecosystems and became ecosystem-creators. The rise of agriculture drastically altered the earth's carrying capacity for H. sapiens, and human populations could increase. For several thousand years after our species became essentially an agricultural granivore, populations of H. sapiens were held in check by occasional famine and by the infectious diseases that co-evolved with densely packed agricultural humanity. However, beginning in the eighteenth century, scientific and technological advances led to increases in agricultural productivity and (temporary?) conquest of many infectious diseases. During the nineteenth and twentieth centuries, human populations grew exponentially, expanding from approximately 1 billion in 1850 to about 6.3 billion in July 2003. Furthermore, at the same time that human populations were increasing so dramatically, each person was, on average, using a greater portion of the world's natural resources. As a result, Wise or Knowing Man has had a devastating impact on most natural systems throughout the world.

Humans dominate the global ecosystem in four primary ways:

Direct transformation of about half the earth's ice-free land for human use. Houses, cities, roads, strip-mines, shopping malls, and highways involve obvious land transformations. Even more surface area is occupied by agricultural systems hostile to almost all living organisms except the monocultural domesticates being produced for food or fiber.
Alteration of the nutrient cycles within the world ecosystem. Globally, the release of nitrogen—through the consumption of fossil fuels and use nitrogen-based fertilizers—is the most critical, though introduction or extraction of other nutrients may be locally important.
Disruption of the atmospheric carbon cycle, particularly through the consumption of fossil fuels. This is the primary cause of anthropogenic climate change.
Introduction of pollutants into the world ecosystem. To this point pollution has had far less impact than the three factors listed above. However, some scientists believe that the accelerated release of pesticides, industrial wastes, and other bioactive chemicals may have increasingly severe ecological consequences. Furthermore, in a world of economic inequality and political instability, a massive infusion of nuclear pollutants is a possibility that should not be discounted.

Mammals at risk

Although the least speciose of tetrapod classes, mammals are also of particular interest to many people. Even if we leave our own species aside, mammals dominate many terrestrial ecosystems as well as some aquatic habitats. Mammals include the largest animal the world has ever known, blue whales (Balaenoptera musculus). Mammals reside atop many food chains, comprise vital links in most terrestrial-vertebrate food webs, and consume primary or secondary production everywhere they occur. Furthermore, perhaps more than any other class of organisms, mammals are threatened by changes occurring at the hand of Wise or Knowing Man. World Conservation

Union (IUCN) data from 2002 suggest that almost one in four mammalian species may be in danger of extinction within the foreseeable future.

When considering threats to biodiversity, we should remember that different species face different threats, and many, if not most species, are menaced by multiple factors. For example, Miss Waldron's red colobus (Procolobus badius waldroni), an African monkey declared extinct in September 2000, suffered intensely from both deforestation and hunting for the bushmeat trade. The black-footed ferret (Mustela nigripes) approached extinction because of habitat conversion, destruction of its prey, and infectious diseases contracted from domestic animals. Sea otters (Enhydra lutris) were exploited for the fur trade and killed by fisherman who considered them competitors for shellfish. And presently, their recovery has been slowed by depredations by killer whales (Orcinus orca). Despite the admitted complexity of extinction processes, we review four principle threats to mammalian species: habitat destruction, direct exploitation, introduction of exotics, and infectious disease.

Habitat fragmentation and destruction

Despite the potential importance of altered nutrient-cycles and pollution, the primary immediate threat to biodiversity is from habitat loss that results from expanding human populations and their economic activities. Habitat loss includes outright destruction as well as habitat disturbance due to fragmentation and localized pollution. In many areas of the world including Europe, China, south and Southeast Asia, Madagascar, Oceania, and much of the United States, most original habitat has already been destroyed. Today the highest annual deforestation rates are in developing and tropical countries, where a large proportion of the world's biodiversity is found. The countries having the highest rates of deforestation in the early twenty-first century are Costa Rica (3.0% annual loss of remaining forest cover), Thailand (2.6%), Vietnam (1.4%), Ghana (1.3%), Laos P.D.R. (1.2%), and Colombia (1.2%). Threats to savannas, grasslands, and freshwater aquatic systems are less well documented, but they are as important as deforestation—and, like deforestation, are concentrated within economically poor countries that are rich in biodiversity. This is a matter considered later in the present essay.

One typical result of environmental alteration is the isolation of habitat fragments, or patches. Fragmentation can reduce or prohibit the dispersal of individuals, and local extinction of some species becomes more likely. Later this essay considers some consequences of habitat fragmentation.

Direct exploitation

Many of the world's natural resources have been over-exploited. Some resources such as fossil fuels are non-renewable, and the best we can do is to slow our depletion of these important commodities. Other resources—such as water, timber, and wildlife—are renewable, and, if used wisely, they may last indefinitely. Unfortunately, people have often been careless about the conservation of renewable resources. The gigantic Steller's sea cow (Hydrodamalis gigas) was first encountered by Europeans in 1741; 27 years later the last individual was killed. The near-extinction of American buffalo (Bison bison) is an example of over-exploitation known to most U. S. school children. The last wild European cow (Bos taurus) was killed in Poland around 1630, and cattle-breeders still decry the loss of important genetic information. Similarly, today in Southeast Asia, at least three species of forest "cow" are in peril of extinction, and these are renewable resources that could still be preserved. During the early and mid-twentieth century, most species of baleen whales were hunted to the edge of economic extinction. Belated protection has allowed species survival, though recoveries have been slow. Great apes, such as gorillas, chimpanzees, and bonobos, are being hunted to extinction for commercial bushmeat in the equatorial forests of west and central Africa. In 2003, it is projected that some 2,000 bushmeat hunters supported by the timber industry infrastructure will illegally shoot and butcher over 3,000 gorillas and 4,000 chimpanzees.

Introduction of exotics

Humans have accidentally and intentionally introduced species into new areas. In a sense, agricultural production itself is a replacement of natural species by domesticated species, under human control. Other examples also abound. Domestic cats (Felis catus) brought by Europeans to Australia, out-competed—or out ate—many small, native marsupials. A small, Australian marsupial (Trichosurus vulpecula, the brush-tail possum) was introduced into New Zealand in 1837. The varmint prospered beyond all expectations, threatening New Zealand's fragile domestic wildlife.

Other familiar examples of unfortunate mammalian introductions include rabbits and foxes into Australia; goats and cats into the Galápagos and Hawaii; rats, goats, and cats into Cuba and Hispaniola (pity the poor Solenodon); mongoose into Jamaica; hogs into too many parts of the southeastern United States; and horses in North America.

Infectious disease

Infectious disease can spread across people, wildlife populations, and domesticated animals. Transmission of infectious agents from domesticated species (e.g., dogs, cattle, water buffalo) to sympatric wildlife can result in a range of potentially fatal infectious diseases. Canine distemper virus is believed to have caused several fatal epidemics among African wild dogs (Lycaon pictus), silverback jackals (Canis mesomelas), and bateared foxes (Otocyon megalotis) in the Serengeti. Populations of African lions (Panthera leo) and cheetah (Acinonyx jubatus) have probably been affected by diseases transmitted from domestic cats. Problems of disease transmission from wildlife to domesticated animals and human beings may also be severe, but they are beyond the scope of this essay.

The nature of conservation biology

Conservation biology is a multidisciplinary science whose overall mission is to conserve biological diversity. The discipline can be subdivided into three primary areas: documenting the world's biodiversity; understanding the nature, causes and consequences of the loss of genetic diversity, populations and species; and developing solutions for the preservation, restoration, and maintenance of biodiversity.

Three ecological postulates that underlie conservation biology

Modern conservation biologists must often transcend the traditional boundaries of academic disciplines, for these scientists increasingly need to know about politics, economics, philosophy, anthropology, and sociology in order maintain or restore the health of ecosystems. However, because conservation biology is fundamentally concerned with the dynamics of wildlife populations, a solid understanding of biology and ecology is paramount for workers within the discipline. Three ecological principles are fundamental for understanding the relationship between population dynamics and conservation.

MANY ORGANISMS ARE THE PRODUCTS OF COEVOLUTION

If most species in an ecosystem were generalists, then in the absence of one generalist species, another generalist species would broaden its niche slightly, and the system would continue to function without important changes. However, if species tend to be specialized, then they are not interchangeable parts in the system; when one is lost, the local ecological community may be affected. For the conservation biologist, interdependent specialization is particularly important, and interdependent specialization often arises through coevolution.

Coevolution involves a series of reciprocal adaptive steps during which two or more interacting species respond to one another evolutionarily. A study of mammalian grazing ecology offers many classic examples of coevolution. Ruminant artiodactyls have evolved fermentation chambers that shelter legions of microscopic flora and fauna. These microbial symbiants extract the energy and nutrients they need from the vegetation consumed by the host-ruminant. In return, the gut-flora ferment cellulose, providing energy and repackaging nitrogen for their hosts. Grazing mammals, in turn, structure the vegetative communities of their grassland habitats. Higher-order coevolution has been demonstrated among

species of grazing ungulates, particularly in Africa. Thomson's gazelles, or "tommies" (Gazella thomsonii), for example, are so small that they cannot effectively exploit the tall grass that grows rapidly after the first rains of the wet season. So, just as other grazers depart the depleted grasslands surrounding a recovering waterhole, tommies move in to exploit the flush of tender, new grass. Eventually tommies disperse to exploit grasslands grazed low by other ungulates (particularly zebra, Equus burchellii, and wildebeest, Connochaetes taurinus). The seasonal ecology, anatomy, and gut flora of G. thomsonii evolved in response to the seasonal ecology of the larger ungulates; without these other animals, populations of the little tommies would be much smaller indeed.

Some species, called keystone species, are especially important for the interdependent functioning of an ecosystem. Keystone species may comprise only a small proportion of the total biomass of a given community and yet have fundamental impacts on the community's organization and survival. The loss of such species may have dramatic and far-reaching consequences in the broader ecological community. Primates and bats are believed to play key roles in maintaining ecosystems through dispersing seeds (some primates), pollinating plants (bats and some primates) and serving as prey items. The loss of these species from ecosystems would be predicted to have deep impacts on ecosystem health. For example, throughout many areas in Trinidad, large mammalian species such as deer,

paca, agouti, and peccaries have been extirpated—and yet the ecosystems still remain functional. On the other hand, within these ecosystems, Trinidad's bat and primate populations may be fulfilling ecological roles for which few other occupants remain. Thus the monkeys and bats may now be keystone species, whose presence is vital to the now-fragile existence of the Trinidad ecosystems. Similarly, in pre-European South Carolina, cougars (Felis concolor) and a large, social canid (Canis sp.) structured the forest herbivores. Now, in the absence of these top predators, whitetail deer (Odocoileus virginianus) obliterate populations of several species of forest herb.

IN ECOLOGICAL SYSTEMS SOME CRITICAL VARIABLES HAVE THRESHOLD LEVELS

Changes in one of these variables may make very little difference in ecosystem operation—until a threshold is crossed, and then dramatic systems-alterations will occur. The mathematical study of nonlinear "threshold relationships" is the province of bifurcation theory, which has been used to model catastrophic phenomena ranging from domestic violence to human heart failure. Many conservation biologists emphasize a particular corollary of this general threshold postulate: some ecological processes may suddenly fail when the landscape patch in which they operate is reduced below a threshold size.

Biologist-activist Paul R. Ehrlich has written several books on ecology and conservation, a recent one is A World of Wounds: Ecologists and the Human Dilemma, Ecology Institute, Oldendorf-Luhe, 1997. He illustrated potential dangers of ecological non-linearities by the following metaphor. Pretend that the world ecological system is an aircraft and that species within the system are rivets holding the aircraft together. If one or two rivets are lost, the aircraft continues to fly as if nothing had happened. More rivets are lost and the airplane still flies. But eventually the loss of "just one more rivet" may bring the flight to a sudden, disastrous end.

GENETIC AND DEMOGRAPHIC SYSTEMS HAVE THRESHOLDS

Like ecological systems, genetic and demographic systems can be nonlinear and have thresholds below which nonadaptive, random processes begin to displace adaptive, "statistically deterministic" processes.

One example of this is the loss of alleles in small populations because of genetic "drift." Another is the extinction of a small population through random binomial processes. This point can be illustrated by an extreme demographic example. Consider a hypothetical species that does not breed during the dry season and suffers high dry-season mortality. More specifically, assume that each female entering the dry season has a 50% probability of surviving until the end of the dry season. Now consider the probable fates of two different populations:

10,000 females enter the dry season. The chances are about 95% that the population at the end of the dry season will include 4900 to 5100 females. In other words, the chances of population extinction are almost exactly 0%. (These statements can be demonstrated by an approximation of the binomial theorem.)
Two females enter the dry season. The chances are about 25% that the population at the end of the dry season will include 0 females. In other words, the chances of extinction for this small population are about 1 in 4.

Conservation biology and three value statements

The three ecological principles listed above form part of the biological foundation for the discipline of conservation biology. In addition, many conservation biologists accept three value statements—which by their very nature are not subject to scientific confirmation or disproof. In other words, conservation biology is inherently a value-laden discipline, and the following assumptions of worth define the ethical positions of many conservation biologists.

DIVERSITY OF ORGANISMS IS ASSUMED TO BE GOOD

Whenever possible conservation biologists defend diversity on utilitarian grounds—and make statements like, "Some little tropical plant may contain a cure for cancer." Furthermore, evidence exists that biological diversity within an ecosystem contributes to the ecosystem's persistence, stability, and productivity. Nevertheless, even without utilitarian support, many conservation biologists would assume that diversity is good in itself (an sich, as the German philosophers used to write) and therefore needs no means-toward-an-end justification. This assumption of intrinsic value is beautifully expressed by Archie Carr in his book Ulendo: Travels of a Naturalist in and out of Africa.

As a corollary to this value principle, most conservation biologists believe untimely extinctions (in general, defined as extinctions that result from human activities as opposed to extinctions that result from natural processes) should be prevented. Most conservation biologists also believe that local biodiversity is a universal good. Thus if desperately poor Madagascar cannot afford to protect the 50 endangered and vulnerable species living within her borders, then perhaps wealthy nations (or individuals) are morally obligated to assist with this conservation enterprise. This idea is returned to later in the present essay.

ECOLOGICAL COMPLEXITY IS ASSUMED TO BE GOOD

Clearly this is related to the first value principle above, but it is not exactly the same thing. Consider, for example, a botanical garden with its specimen trees and its greenhouses. Such an installation might contain more different species than a tropical rainforest (and thus would satisfy the principle that "diversity of organisms is good"), but it would not manifest the complex web of inter-organism relationships that characterize a tropical rainforest. The conservation biologist would likely prefer the rainforest to the botanical garden. Or consider this value principle in the form of a question. Some authorities believe that fewer than 1,000 species of large mammals can be preserved from extinction only in captivity. Will a typical conservation biologist be completely satisfied if these mammals survive only in zoos?

EVOLUTION IS ASSUMED TO BE GOOD

The diversity of organisms and the ecological complexities of their interrelations are products of evolution. Most conservation biologists affirm not only the value of the product but also the value of the process that made it. Let us see how this value principle might affect the political agenda of a conservation biologist. What if the wildlife-refuge systems of the world were sufficiently extensive to preserve every living species: would the conservation biologist be satisfied if refuges were not large and diverse enough to allow continued speciation (evolution)?

What areas are the most important to preserve?

Questions of "conservation triage" are difficult, but they must be faced in a world of limited support for conservation agendas. Faced with this problem, British ecologist Norman Myers devised the concept of biological "hotspots," which he defined as regions particularly rich in endemic species and immediately threatened by habitat destruction. Myers is the author of 17 books on the environment, among them Gaia: An Atlas of Planet Management, 1993. Myers listed 25 particularly important hotspots, which total only 1.4% of the earth's land surface, but contain 44% of all plant species and 35% of all terrestrial vertebrate species. The Indo-Burma hotspot covers

approximately 795,000 mi² (2,060,000 km²) in south and Southeast Asia, and is home to such threatened species as tigers (Panthera tigris), red-shanked douc langurs (Pygathrix nemaeus), Sumatran and Javan rhinoceros (Dicerorhinus sumatrensis and Rhinoceros sondaicus), and Eld's deer (Cervus eldi). However, only 61,780 mi² (160,000 km²), or 7.8% of the total area, is protected. Myers's favored strategy would be for conservation organizations to focus their efforts for fundraising and biodiversity conservation upon these areas, and such organizations as Conservation International and the MacArthur Foundation now largely subscribe to the hotspot approach.

However popular it may become, hotspot triage is not without its problems and detractors. For example, some readers may be surprised to learn that rainforests in the Amazon and Congo Basins do not make the magic Top-25. These areas, of course, are rich in endemic species—but they maintain over 75% of their forest cover and are in no immediate danger of complete destruction. Hotspot advocates would argue, "We should spend scarce dollars on species-rich real estate that's about to be destroyed." Opponents might reply, "I'd rather spend scarce dollars on species-rich Amazonia while I can still afford a really big chunk of it."

Regardless of her or his affection for (or disaffection with) hotspot triage, any mammalogist concerned with long-term conservation should become familiar with the types of habitats most important to mammalian diversity and most severely threatened with destruction. Such habits include tropical rain-forests, tropical deciduous forests, grasslands, mangroves, and aquatic habitats.

During the 1980s and 1990s, tropical rainforests captured an increasing share of public attention. Rainforests cover less than 2% of the earth's surface, yet they are home to over 40% of all macroscopic life forms on our planet—as many as 30 million species of plants and animals. Rainforests are quite simply the richest, oldest, most productive, and most complex ecosystems on Earth. Furthermore, many of them, particularly in Asia and Oceania, are increasingly threatened by destruction.

Because they are more amenable to sedentary agriculture, some tropical deciduous forests are even more severely threatened than rainforests. Tropical savannas, with their magnificent relics of the Pleistocene mammalian megafauna, are easily converted into pasturelands—and unspoiled tropical savannas scarcely exist at all outside of formal National Parks. Mangroves, which shelter a number of important mammalian species, such as proboscis monkeys (Nasalis larvatus), are threatened by pollution, conversion for intensive aquaculture, and destruction for firewood. Lakes, rivers, estuaries, seacoasts, and other aquatic habitats are also under increasing threats of multiple dimensions.

A problem faced by most conservation biologists working in the international arena is that countries with the highest degree of biodiversity (and this is particularly true for threatened and endangered mammals) are usually the countries least able to afford the conservation of their natural resources. For example, in some areas the median per capita income is less than __BODY__US per day. People living under these conditions often consider conservation to be an unaffordable luxury.

Of course conservation biologists have long recognized that the futures of tropical peoples and of tropical wildlife are inextricably mixed. And for more than a decade almost all conservation action plans have emphasized the fact that local people should have an economic stake in the protection of their wild resources. Zimbabwe's "Campfire" program provides a classic example of the local benefit philosophy in action. Village councils were given authority to manage wildlife resources. Then, for example, when Europeans or Americans came to Zimbabwe to kill elephants, the villages could profit from the substantial expenditures of the wealthy hunters. Unfortunately, Campfire (and related "eco tourism" plans) is selling a high dollar luxury activity—which is at the mercy of international market forces and local interference. International economic downturns or national instability (both of which have beset Campfire) can undermine value-added conservation programs.

Under some circumstances sustained-yield harvest programs that return valued wild products directly to local users can be successful. Nevertheless, among people who are desperately poor, the odds against such programs are high. Many impoverished people naturally think of wild mammals as meat—not as an abstract food-resource to be harvested on a long-term, sustained-yield basis but as meat, now, for children who will otherwise be far too hungry before nightfall. The sale of bushmeat is rapidly becoming a substantial source of income, as well.

Because many conservation biologists believe that local biodiversity is a universal good, some argue that wealthier nations (and individuals) have a moral duty to assist poorer nations in conserving humanity's general biodiversity heritage. Even if one subscribes to this idea, it is difficult to determine (particularly on personal, financial levels) the degree of sacrifice that is morally obligatory. Furthermore, in recognizing that severe poverty threatens conservation, there are two more fundamental facts:

First, severe poverty is in part a function of inequality. In 2003 the United States contains about 5% of the world's people—but is responsible for 30% of the world's resource-consumption. It is difficult for Americans to preach conservation to the rest of the world until the United States begins to clean up its own house.
Second, severe poverty is in part a function of population-size. If the economic "pie" is finite in size, then even if the pie were equitably shared, "more people" would mean "smaller pieces per capita." At some point, population control becomes a prerequisite to effective conservation policy.

Conservation biology, habitat fragmentation, and island biogeography

The theory of island biogeography was formulated to explain how rates of colonization and extinction affects species diversity observed on actual islands. Currently, protected areas (such as national parks, to which many threatened mammalian species are increasingly restricted) are beginning to resemble habitat-islands in vast seas of agricultural or even urban development. Therefore, island biogeography is increasingly considered an intellectual tool with which conservation biologists should be familiar.

The basic theory of island biogeography grew out of two empirical observations: (1) larger islands often have more species than small islands, and (2) an island's distance from the nearest continent is inversely related to the island's species diversity. These observations were eventually brought together into the equilibrium theory of island species diversity. Conservation biologists use insight from this theory in the management of fragmented landscapes. In particular they often ask how small a refuge "island" can be, before threshold effects arise and species-extinctions dominate community dynamics.

Basically, if a habitat-patch is too small to include home ranges for a viable population of a mammalian species, then the long-term survival of that species is improbable. Information about extinction rates of small mammals in habitat fragments is difficult to evaluate, in part because biologists lack comparable data from undisturbed habitats to serve as controls. However, two studies on forest fragments provide disturbing evidence that mammalian diversity can decline quickly:

Short term, Thailand. In Surat Thani Province approximately 100 islands were created in 1986 when the Saeng River was dammed to create a hydroelectric reservoir. Rapid changes occurred in the small mammal assemblages on these new islands. Within five years, two of the 12 species (a murid rodent, Leopoldamys sabanus and an insectivore, Hylomys suillus) were lost. Further extinctions are likely.

Long term, Panama. Early in the twentieth century, several forest hilltops were isolated during the damming of the Chagras River during the construction of the Panama Canal. After 80 years of isolation, only one out of 16 rodents species remained on islands smaller than 42.3 acres (17.1 ha). The rate of mammalian species-loss from these small island-fragments was approximately one species per 3–11 years.

The fate of large mammal communities in small habitat-fragments is even grimmer. Most big mammals must have a great deal of space. For instance, the home range of a Southeast Asian rhinoceros (Rhinoceros sondaicus annamiticus) in Cat Tien National Park, Vietnam has been estimated at 1,480–2,470 acres (600–1,000 ha). Some solitary carnivores require areas an order of magnitude larger. A tiger, for instance, might roam across more than 24,700 acres (10,000 ha), and a single wolverine (Gulo gulo) would probably need twice that much room.

These are area-requirements for individual mammals, while of course, viable populations are comprised of many individuals. These populations need even larger patches of habitat. For example, many species of African grazing artiodactyls can exhibit their natural social behavior only in large groups. Large groups require enormous areas, sometimes with widely separated dry-season and wet-season ranges. The

annual migration of east African wildebeest (Connochaetes taurinus) covers hundreds of miles (kilometers) and crosses national borders. Of course wildebeest can be kept alive in modest pastures, and tigers can be maintained in zoo-cages. But these conditions are not fully satisfactory and clearly only the largest national parks allow viable populations of most mammals to exist in natural social conditions.

Conserving such large tracts of habitat is often difficult. One approach is to connect habitat fragments by means of corridors, or protected habitat-strips that allow animals to move between patches. In Africa it has been observed that some mammals (as well as reptiles and birds) use corridors as inter-patch bridges. However, some conservation biologists question whether this phenomenon is at all general.

It should be clear that as conservationists contemplate the establishment, enlargement, or maintenance of a refuge, they should be aware of the particular needs of those target organisms that the refuge is designed to shelter. Behavioral ecologists, for example, often gather data on a species' activity patterns, foraging behavior, group size, home range, and territorial behavior. Such information is useful for predicting how a target species will respond to habitat fragmentation, how edge-effects will impact a given species, or whether the species will use habitat corridors.

Genetic concerns about small populations

The discussion of thresholds bemoaned the fact that small populations were at risk of extinction by demographic stochastic processes. Efforts to maximize intra-specific genetic diversity are a high priority for conservationists. In general, genetic diversity is correlated with population size. Thus larger populations should manifest a greater variety of phenotypes—and should therefore be better able to respond to variations in environment. However, with habitat loss and fragmentation, populations of many mammalian species are declining and are being fractured into small, disconnected units. And as populations shrink, genetic variation may be lost.

Loss of genetic variability from a population is primarily a function of three interrelated phenomena: "bottlenecking," random genetic drift, and inbreeding depression.

Bottlenecks are events that greatly reduce a population's size. Such reductions can have many causes, including habitat alteration or loss, introduction of competitors or predators, and the spread of epidemic disease. The individuals that survive a bottleneck are the founders for all future generations, and only the genetic variability that is represented in these founder-individuals (plus subsequent mutations) can be preserved within the species. The cheetah (Acinonyx jubatus) is the classic example of a bottleneck species. A population crash some 10,000 years ago radically reduced genetic variability. Even today all cheetahs remain so similar, genetically, that skin transplants from one animal to another are not rejected. More significant, cheetahs may lack the genetic variability to respond, evolutionarily, to new diseases confronting the species. But a large population size can usually overcome problems of low genetic variation, as is the case with the current populations of elephant seals, for example.

In evaluating a bottleneck, conservation biologists are especially concerned about the effective population size, or N_e, which is (roughly) the number of breeding animals in a population. N_e is generally smaller than the number of individuals in the population—and if breeding animals are closely related, it can be much smaller indeed. For example, two sets of identical twins do not count as four complete animals, for genetic purposes. The rate of a population's heterozygosity-loss, per generation, is largely a function of effective population size. That is to say, the amount of genetic variability preserved from one generation to the next is approximately proportional to (1 − 0.5 N_e). Obviously, when N_e is large, the majority of genetic variability will be maintained, and when N_e is small, heterozygosity can be lost very rapidly.

Clearly, even the tightest bottlenecks need not be fatal to a population's survival. Every mammalian species began from a minimal founder-size, and if a bottlenecked population is allowed to increase greatly in numbers, any decay in genetic diversity can be balanced by new variability added through mutation. The most serious problems arise when the bottleneck-squeeze is maintained over multiple generations, because in this case (1) loss of variability by genetic drift vastly exceeds replacement by mutation, and (2) this process is accelerated by inbreeding. An example is the lowered allozyme and DNA variability observed in the brown hares (Lepus europaeus) of New Zealand and Britain and attributed to bottlenecks.

Random genetic drift, sometimes called the Sewall Wright effect, designates changes in a population's allele frequencies due to chance fluctuations. Random genetic drift becomes important only when populations are small. Cross-generational transfer of alleles is then subject to sampling error, and a given allele can be lost (decline to 0% frequency) or fixed (increase to 100% frequency). In other words, when small populations of a species are isolated, out of pure chance the few individuals who carry certain relatively rare genes may fail to transmit them. The genes can therefore disappear and their loss may lead to the emergence of new species, although natural selection has played no part in the process. And the smaller a bottleneck, the more rapidly genetic drift can operate. The longer a bottleneck persists, the greater the potential cumulative effects of genetic drift.

Inbreeding depression can result from matings between close relatives and is more likely to occur in a small population confined to a small habitat-patch. The deleterious effects of inbreeding have been repeatedly documented in zoo populations, before the implementation of genetic management programs. For example, inbred calves of Dorcas gazelle (Gazella dorcas) suffered from high juvenile mortality and delayed sexual maturity of females. Among wild populations, inbreeding depression in Florida panthers (Felis concolor coryi) may have lowered reproductive rates and reduced the species' capacity to respond to disease.

Przewalski's horse (Equus caballus przewalskii) is the only surviving variety of wild horse. This animal is considered extinct in nature (wild individuals were last observed in 1969) and survives only because of captive breeding. The founder-stock for the captive herd was limited in number. Therefore, genetic drift and inbreeding depression have led to a loss of genetic diversity in E. c. przewalskii and are reflected by high juvenile mortality and a reduced lifespan. International management programs aim to retain 95% of the current average individual heterozygosity for at least 200 years. And a program is underway to reintroduce these animals into Mongolia.

Wildlife

Conservation medicine focuses on the changing health-relationships between people, other animals, and shared ecosystems. Of course every variety of mammal has been affected by diseases and parasites throughout its species-history. And across evolutionary time, mammalian species have established accommodations with pathogenic organisms: immune and behavioral defenses evolve in the host; responses (often including transmission "improvement" and reduced virulence) co-evolve in the pathogen. However, the present age—with its fragmented populations of wild mammals and anthropogenic mixing of previously separate species—has destabilized these

dynamic equilibria. And the results are of concern to conservation biologists.

In recent years several emerging infectious diseases (EIDs) have been identified in wildlife populations. Among immunenaive populations, these EIDs may inflict direct mortality beyond a species' evolved capacity for demographic response. In addition, EIDs may affect reproduction, susceptibility to predation, and the competitive fitness of infected hosts. When these detrimental effects extend to the population level, they may in turn affect community structure by altering the relative abundance of species.

Habitat fragmentation often places wildlife species in closer proximity to domesticated animals because habitat patches may be adjacent to farms, villages, and even urban areas. Such situations can facilitate cross-species contagion of disease. People have transmitted tuberculosis, measles, and influenza to gorillas (Gorilla gorilla), orangutans (Pongo pygmaeus), ferrets (Mustela putorius furo), and other mammals. The slaughter of primates for bushmeat in Africa was probably

the first exposure of people to the precursor of human immunodeficiency virus (HIV). Lions in the Serengeti have been affected by diseases of cats and dogs from Tanzanian villages. In 1984 a disease caused by calicivirus was detected among rabbits in China. The origin of the disease is not definitively known, but the pathogen soon spread westward into Europe, where it affected perhaps 90% of the rabbit populations. Rabbit calicivirus is now used as the primary means for controlling feral rabbits in Australia. (Earlier control relied mainly in the introduction of myxomatosis virus among Australian rabbits. In the 1950s, myxomatosis had a kill-efficiency of about 99%. Over time, however, Australian rabbit populations evolved immunity.) Efforts to re-establish wild populations of black-footed ferrets (Mustela nigripes) in western North America have been hampered by the spread of cat and dog diseases among the ferrets, and because enormous populations of ferret prey (prairie dogs) had been destroyed by sylvatic plague.

Because human health may be increasingly affected by diseases transferred from wildlife, conservation medicine is likely to become an important area of research for conservation biologists.

Ex situ conservation issues: demand, consumption, and captive breeding

Much of this essay has focused on in situ conservation problems because the most important conservation battles will likely be fought on the home grounds of the target species. Nevertheless, the importance of ex situ conservation issues should not be underrated. Ex situ issues are of two very different types.

Issues of demand and consumption

The impact of economic factors on conservation must be recognized as well. As mentioned earlier, human poverty undercuts conservation programs near many of the world's biodiversity hotspots, but economic factors can affect conservation even from a distance. Research on west Africa's bush-meat trade shows that if markets for meat are exclusively local, the impact of hunting is relatively limited. However, if bush-meat becomes a commodity in a nation's general capitalist economy (if, for example, a market for bushmeat develops in a large city), then demand for forest animals becomes practically unlimited, and vulnerable species may be hunted to extinction. Similarly (here a non-mammalian example), the perilous condition of Southeast Asia's hitherto magnificent chelonian fauna is primarily a function of China's emergence as the regional economic superpower—and of China's insatiable demand for turtle products. Sometimes economic influences can be somewhat less direct. An analysis of the Japanese whaling industry in the 1950s and 1960s indicated that commercial species could be harvested at reasonable profits indefinitely, on a sustained-yield basis. However, the rate of whale-replenishment (r in the population growth equations) was slower than the rate of Japan's economic growth. Therefore, it made good business-sense for commercial whalers to "liquidate their investments" in whales (i.e., to hunt them out) and reinvest their yen in sectors of the Japanese economy yielding higher rates of "interest."

It is hoped that many conservation-and-economics dilemmas may eventually yield to analysis by economically sophisticated conservation biologists—or even by "conservation economists." That is, sustainable development programs combining people, profits, and wildlife may yet save the day. However, in the long run Wise or Knowing Man must develop a new conservation ethic—of sharing, sacrifice, appreciation, and awe—if an appreciable portion of mammalian biodiversity is to be preserved. In other words, why read Phillips and Abercrombie instead of re-reading Aldo Leopold (A Sand County Almanac first published in 1949) and Archie Carr?

Captive breeding and reintroduction

In recent years ex situ conservation efforts have become increasingly important. Zoos, botanical gardens, wildlife parks, and conservation trusts now work in collaboration to maintain captive assurance colonies of threatened plants and animals. Studbooks on target species are kept by participating institutions, and breedings are scheduled in consultation with conservation geneticists.

The proximate mission of ex situ colonies is to maximize genetic diversity within a captive population of affordable size. Long-term, however, the fundamental conservation goals of captive breeding are release-in-habitat with the skills necessary for survival—and eventual reestablishment of viable wild populations within target species' historical ranges. Captive propagation definitely works, and more threatened species are now bred in zoos, etc., than ever before. On the other hand, reintroductions (as well as related programs such as translocation of wild animals) have enjoyed only mixed success.

The case of the giant panda (Ailuropoda melanoleuca) may be instructive. Today only about 1,000 of these magnificent animals survive in the mountain forests of central China. Years of environmental degradation, disease, and depredation have taken their toll on A. melanoleuca. Furthermore, within the animals' fragmented habitat, post-flowering bamboo die-offs have added malnutrition to the pandas' tale of woe. Presently, about 140 giant pandas are maintained in Chinese zoos and in other breeding facilities around the world. However, despite the infusion of massive amounts of money, captive breeding programs have met with only limited success. Of the 226 giant pandas born in captivity between 1963 and 1998, only 52% survived for as long as a month, and others died before they reached reproductive maturity. At present the captive population is scarcely self-sustaining, and it may not produce appreciable numbers for release within the foreseeable future.

By contrast, captive propagation and reintroduction have been more successful with the golden lion tamarin (Leontopithecus rosalia), a small primate endemic to the Atlantic coastal forests of eastern Brazil. Because of over-exploitation and (particularly) habitat destruction, this tamarin had become endangered by the late to mid twentieth century. Beginning in 1984, scientists from Brazil and the United States began reintroducing zoo-born golden lion tamarins back into their habitat in the wild—primarily onto private lands that could be protected against the ravages of timber harvest. The combined efforts of governments, nongovernmental organizations (NGOs), local communities, zoological parks, and conservation scientists have more than doubled the size of the wild golden lion tamarin population.

A review of 116 reintroductions (89 involved mammals; all were carried out between 1980 and 2000) concluded that 26% succeeded and 27% failed. (The remaining 47% were classified as uncertain.) Many factors influence reintroduction success. These include habitat quality, the number of individuals released (there is no magic number, but 100 has become the rule of thumb), and the density of predators. Before any reintroduction is attempted, however, conservationists should identify and eliminate the cause of the target species' initial decline. If this can be done, then a reintroduction has a reasonable chance of success. Otherwise, a reintroduction may provide opportunities for feel-good press releases, but it is unlikely to result in establishment of a viable wild population.

Translocation involves moving wild animals from one place to another and therefore is, in a sense, an ex situ activity. Sometimes translocations are attempted without adequate preparation. For example, in French Guiana, howler monkeys (Alouatta seniculus) were translocated because their habitat was to be flooded by the construction of a hydroelectric dam. These individuals were moved to an area where howler numbers had been reduced by hunters—and where hunting still occurred. In other words, the cause of the original population decline had not been addressed, and the success of the translocation is still in doubt.

The translocation of Asian rhinoceroses (Rhinoceros unicornis) in Nepal is a happier story. Nepali government biologists, assisted by World Wildlife Fund for Nature (WWF), U.S. Fish and Wildlife Service (USFWS), and the King Mahendra Trust, captured rhinos in Royal Chitwan National Park and transported them 220 mi (350 km) cross-country to Royal Bardia National Park. The receiving park was within the Asian rhino's historic range. Habitat was excellent (in quality and quantity), and although R. unicornis had been extirpated from Bardia by poachers, the park was well protected by the time the reintroduction project began. Rhino translocations have continued for a decade, and now conservation biologists believe that Nepal has successfully established a second viable population of R. unicornis.

Translocations of wild animals are often attempted for reasons unrelated to conservation. While conservationists may not generally support the movement of wildlife to solve human-animal conflicts, they can sometimes learn valuable lessons from such activities. For example, nuisance brushtail possums (Trichosuros vulpecula) moved from the city of Melbourne into the Australian outback suffered heavy depredation. Similarly, small, endangered mammals, raised in a zoo, might require some sort of predator-avoidance training before they were released into areas with high predator densities. White-tailed deer (Odocoileus virginianus), captured for translocation when the Florida Everglades were in flood, generally did not survive the ordeal. From this experience some biologists learned a great deal about the importance of minimizing capture-trauma when dealing with mammals already under severe stress. Translocations of nuisance raccoons (Procyon spp.) and black bears (Ursus americanus), though perhaps unwise, reinforce the lesson that some animals know how to get home—and will walk a very long way to get there.

Evaluating the success of conservation projects

This essay is not intended to offer instructions on how to conduct a conservation program. Decisions about supporting conservation are important and they should be made conscientiously on the following basis: "Evaluate with a critical mind, and then support with an open heart."

IT IS MOST IMPORTANT TO EVALUATE THE CANDIDATE'S OR ORGANIZATION'S EFFICIENCY AND INTEGRITY

In this day and age, almost every political candidate will claim to be a great supporter of conservation. Every "Save the Whatever" organization employs experts who design mail-out appeals that are aesthetically elegant and read as sincerely as the Sermon on the Mount. Most readers of this essay are sophisticated enough to see beyond political hype. Also, almost every U. S. state (and many national governments around the world) has a consumer advocate office that can help evaluate the non-profit organizations that solicit conservation contributions. Typically these consumer advocate offices can provide information on the percentage of contributions that go to support actual conservation activities (as opposed to paying staff personnel, for example). They can almost always warn of organizations that support outright frauds.

IT IS IMPORTANT TO EVALUATE THE PROGRAM ADVOCATED BY A CANDIDATE OR CONSERVATION ORGANIZATION

A key to evaluation is to determine whether an organization's stated objectives are meaningful and realistic. Here are four hypothetical statements of objectives that should be questioned:

Elephants are in terrible danger, and your contribution will save the lives of countless elephants in southern Africa. The organization should offer some idea of how the promise will be fulfilled. Furthermore, words like "countless" should ring loud alarm bells.
If I am elected, I will protect lands in such a way as to conserve functioning ecosystems in which living organisms can interact in complex ways. Every living system—from rice fields to rainforests to urban gardens to septic tanks—meets this criterion. This is a meaningless promise, since it will automatically be kept.
The goal of our policy is to preserve appropriate natural, aesthetic values for future generations. Both authors of this essay are teachers. Part of our job is evaluation, and we don't give tests that we cannot grade. Thus we are wary of claims that cannot be checked. We like the idea of preserving values—but we wouldn't offer our votes or our dollars until we learned many more specifics.
The objectives of this program are to integrate economic and intrinsic wildlife values in a holistic program that recognizes human rights to sustainable development and national responsibilities for conservation of biodiversity. This statement sounds great. It uses most of the favorite vocabulary words of the conservation community. However, we have no idea what the statement means—and we wrote it. We would certainly look for specific, measurable objectives before we were tempted to support such a program.