|End of the Wild
The extinction crisis is over. We lost.
Stephen M. Meyer
8 For the past several billion years evolution on Earth has been driven by small-scale incremental forces such as sexual selection, punctuated by cosmic-scale disruptions?plate tectonics, planetary geochemistry, global climate shifts, and even extraterrestrial asteroids. Sometime in the last century that changed. Today the guiding hand of evolution is unmistakably human, with earth-shattering consequences.
The fossil record and statistical studies suggest that the average rate of extinction over the past hundred million years has hovered at several species per year. Today the extinction rate surpasses 3,000 species per year and is accelerating rapidly?it may soon reach the tens of thousands annually. In contrast, new species are evolving at a rate of less than one per year.
Over the next 100 years or so as many as half of the Earth's species, representing a quarter of the planet's genetic stock, will either completely or functionally disappear. The land and the oceans will continue to teem with life, but it will be a peculiarly homogenized assemblage of organisms naturally and unnaturally selected for their compatibility with one fundamental force: us. Nothing?not national or international laws, global bioreserves, local sustainability schemes, nor even "wildlands" fantasies?can change the current course. The path for biological evolution is now set for the next million years. And in this sense "the extinction crisis"?the race to save the composition, structure, and organization of biodiversity as it exists today?is over, and we have lost.
This is not the wide-eyed prophecy of radical Earth First! activists or the doom-and-gloom tale of corporate environmentalists trying to boost fundraising. It is the story that is emerging from the growing mountain of scientific papers that have been published in prestigious scientific journals such as Nature, Science, and the Proceedings of the National Academy of Sciences over the past decade.
The Real Impact
Through our extraordinary capacity to modify the world around us, we human beings are creating a three-tiered hierarchy of life built around human selection. The great irony here is that this anthropogenic transformation of the biosphere springs as much from our deliberate efforts to protect and manage the life around us as it does from our wanton disregard for the natural environment.
At one extreme we are making the planet especially hospitable for the weedy species: plants, animals and other organisms that thrive in continually disturbed, human-dominated environments. (I borrow this term from David Quammen's seminal A Planet of Weeds.) Many of these organisms are adaptive generalists?species that flourish in a variety of ecological settings, easily switch among food types, and breed prolificly. And some have their needs met more completely and efficiently by humans than by Mother Nature. In the United States, for example, there are five times as many raccoons (Procyon lotor) per square mile in suburban settings than in corresponding natural populations in "the wild."
From dandelions to coyotes, weedy species will enjoy expanding populations, spatial distribution, ecological dominance, and opportunities for further speciation into the far future. Many of these species have become so comfortable living with us that they have been labeled pests, requiring stringent control measures: the common (Norway) rat (Rattus norvegicus) and white-tailed deer (Odocoileus virginianus) come immediately to mind.
Living on the margins in ever-decreasing numbers and limited spatial distribution are relic species. Relic species cannot thrive in human-dominated environments?which now nearly cover the planet. Facing the continual threat of extinction, relic species will linger in either ecologically marginalized populations (e.g., prairie dogs and elephants) or carefully managed boutique populations (e.g., pandas). Most, including the Sumatran rhinoceros (Dicerorhinus sumatrensis), the California condor (Gymnogyps californianus), and virtually all of Hawaii's endemic plants, will require for survival our permanent, direct, and heavy-handed management, including captive breeding and continuous restocking.
Other relics, such as rare alpine plants, may survive in isolated patches through benign neglect. Over time they will experience progressive genetic erosion and declining numbers, and will rapidly lose their ecological value. In essence, they will be environmental ornaments.
But a large fraction of the non-weedy species will not be fortunate enough to have special programs to extend their survival or will be incapable of responding to such efforts. These are the ghost species?organisms that cannot or will not be allowed to survive on a planet with billions of people. Although they may continue to exist for decades, their extinction is certain, apart from a few specimens in zoos or a laboratory-archived DNA sample.
Some, such as the East Asian giant soft-shell turtle (extirpated except for one left in the wild) and the dusky seaside sparrow (extinct), are incapable of adapting their highly specialized needs rapidly enough to keep up with human-induced pressures. Others we intentionally try to eradicate. Although they are now protected, wolves and black-tailed prairie dogs in North America were once hunted for extermination as part of federal and state animal-control programs (and unofficially, they still are). In Africa, the lion population has plunged from over 200,000 in 1980 to under 20,000 today due to preemptive eradication by livestock herders.
Still other prospective ghosts we simply consume beyond their capacity to successfully reproduce?for food, for commercial products, or as pets. Recent reports suggest that we have consumed 90 percent of the stocks of large predatory fish, such as tuna and swordfish, in the world's oceans. And while 10,000 tigers live as private pets in the United States, fewer than 7,000 live in the wild throughout the world!
A great many of the plants and animals we perceive as healthy and plentiful today are in fact relics and ghosts. This seeming contradiction is explained by the fact that species loss is not a simple linear process. Many decades can pass between the start of a decline and the collapse of a population structure, especially where moderate-to-long-lived life forms are involved.
Conservation biologists use the term "extinction debt" to describe this gap between appearance and reality. In the past century we have accumulated a vast extinction debt that will be paid, with interest, in the century ahead. The number of plants and animals we "discover" to be threatened will expand out of control as the extinction debt comes due.
Thus, over the next hundred years, upwards of half of the earth's species are destined to become relics or ghosts, while weedy species will constitute an ever-growing proportion of the plants and animals around us. By virtue of their compatibility with us, weedy species can follow us around the planet, homogenizing (in both plausible interpretations of the word) the biosphere by filling in the spaces vacated by relics and ghosts. More and more we will encounter on every continent remarkably similar, if not the very same, species of plants, insects, mammals, birds, and other organisms.
How Did We Get Here?
Although we have been aware of species losses for decades, only recently has it become apparent that the biotic world as we have known it is collapsing. The causes, varied and complex, fall into three broad disturbance categories: landscape transformation, geochemical modification (pollution), and biotic consumption and manipulation. Each reflects some aspect of human-induced manipulation of the environment, as these examples from the news show:
New housing developments in Scotland will destroy critical habitat for Britain's threatened red squirrel (Sciurus vulgaris), which has disappeared from most of its former range.
Logging and agricultural development have reduced the distribution of Chile's famed national tree?the monkey puzzle tree (Araucaria araucana)?to three small areas of the country, where it is vulnerable to fire and illegal logging.
A new dam in Belize will flood vital habitat for rare species of jaguars, macaws, and crocodiles in a valley linking to wildlife preserves.
Biologically active quantities of common over-the-counter and prescription drugs (e.g., Prozac) are ubiquitous in European and North American urban and suburban waste waters, where discharge to streams and rivers wreaks havoc on aquatic animal endocrine systems.
Polar bears endure body concentrations of PCB and other industrial toxins hundreds of times higher than those of animals living where the pollutants are emitted, thousands of miles away.
Eighty percent of Caribbean corals have died off in the past two decades from diseases fuelled by nutrient pollution from municipal waste-water treatment plants and agricultural runoff flooding into coastal waters.
Demand for "bush meat" in Africa (which sells for 30 percent of the price of farmed meat) is now outstripping supply, seriously depleting wildlife populations in general and great apes in particular. Meanwhile the international trade in bush meat and animal parts is growing exponentially, fetching prices many times those in domestic markets.
During the past two years half of the world's remaining Amur tigers (Panthera tigris altaica) were wiped out by trophy hunters, leaving fewer than 300 animals in the wild?ensuring the extirpation of the species.
Collecting freshwater and marine fish for the aquarium trade reduces wild populations of targeted species by 75 percent in commercial collection areas.
Cheatgrass, introduced into North America around 1900, has displaced native vegetation across broad areas of rangeland in western North America, devastating the local ecology. A prolific annual of low nutritive value, cheatgrass dries up early in the season, fueling extensive range fires that wipe out native plants and leave little food or shelter for wildlife.
Native aquatic food webs in South America are being destroyed by the introduction of the North American bullfrog (Rana catesbeiana)?a voracious predator.
When these factors?development, agriculture, resource consumption, pollution, alien species, etc.?are considered separately, the problem seems quite manageable. Sprawl can be fixed with smart growth. The demand for agricultural land and high-intensity farming can be dampened through dietary changes. Natural resource over-consumption in logging, hunting, fishing, and the exotic pet trade can be reduced through education, regulation, and policing. And the proliferation of alien species can be stopped through better laws and inspections. But this is a gross simplification: the appearance of tractability is created only by taking the causes one at a time.
Consider the plight of a simple, undemanding, and modestly adaptable creature: the California tiger salamander (Ambystoma californiense). These amphibians live most of the year underground in upland fields and woodlands. Each winter they migrate thousands of feet to their natal breeding pools to find mates and lay eggs. After several weeks of carousing they return to their underground burrows in the surrounding uplands.
The key to the breeding success of these salamanders is the ephemeral nature of the pools. The pools exist as dry depressions for six months of the year. Then, as heavy spring rains flood the region, these shallow basins fill with water, creating vernal pools. Tiger salamanders have come to rely on these temporary pools because, since they are dry part of the year, they cannot support naturally occurring fish populations. Thus, the salamanders' eggs are relatively safe from predation. As the eggs hatch, the larvae find themselves immersed in a bath of food: the water is bursting with millions of planktonic organisms. The salamander larvae grow rapidly?and they need to, because with the rains gone the pools dry up quickly, and unless the juvenile salamanders mature and move out into the surrounding terrain they will die. And so it has been for millions of years.
But not anymore. Today the California tiger salamander is disappearing. First, the upland habitat where it lives is prime real estate for residential, commercial, and agricultural development. Between 50 and 75 percent of its native habitat has already been lost, and more than 100 development projects are pending in the remaining areas. Woodlands are cut down and fields plowed up to make room for houses, lawns, schools, shopping centers, and roadways. Many vernal pools themselves are simply filled.
Where pools are spared bulldozing they are pressed into service as roadside storm basins to collect runoff from lawns, roads, and driveways?water saturated with fertilizers, herbicides, pesticides, and heavy metals. The nitrogen and phosphorus in the runoff stimulates massive algal blooms that drives oxygen levels in the pools down to deadly levels, suffocating a large proportion of the animals. High concentrations of herbicides and pesticides in the runoff kill many juveniles and, in lower doses, alter metabolic chemistry in ways that bizarrely change sexual development, immune function, and even limb development.
Even setting aside local sources of contamination, the water in the pools is increasingly laden with a cocktail of toxic compounds (e.g., the herbicide atrazine) that are not used locally. Blowing in from industrial and agricultural sites many hundreds of miles away, these endocrine-disrupting compounds significantly reduce breeding success and foster grotesque developmental abnormalities.
Then there is the army of alien species?bullfrogs, crayfish, and other predators?that have been introduced intentionally into the landscape. These voracious hunters consume huge numbers of salamander larvae and juveniles, further decimating the tiger salamanders. In some instances, non-native salamanders (former pets) have been released into local pools, reducing breeding success and posing the risk of hybridization. And fish are frequently added to the temporary pools to devour mosquitoes during the wet season. While this makes life more comfortable for nearby human inhabitants, it exhausts the young salamanders' food supply.
But the assault does not end there. The regularity of spring rains is being replaced by recurrent three- and four-year droughts. Several generations of tiger salamanders therefore never emerge to replace the animals lost to natural and unnatural causes. In the past, tiger salamanders persisted despite climate variations by virtue of wandering individuals who trundled aimlessly through networks of wetlands until they chanced upon new vernal pools and restarted the population. But that is no longer possible because the matrix of connecting wetlands has been eliminated, and habitat fragmentation makes the chance encounter with a car tire many orders of magnitude greater than an encounter with either a suitable mate or a suitable habitat.
Finally, where residual populations of tiger salamanders have survived despite the odds in still isolated locations, they have become a target of the pet trade. Children are paid 25 cents per salamander to collect these highly prized animals, which are then sold for $15 a piece in U.S. pet shops and for more than $200 overseas. In fact the global trade in "exotics" such as tiger salamanders is growing explosively, especially for reptiles and amphibians. Probably one in a thousand salamanders survives the commerce and perhaps one in a thousand of these survives a few years in captivity.
This story is neither fictional nor unique. It is, in fact, the rule. One could tell similar stories of the red-crowned crane (Grus japonensis), the leatherback sea turtle (Dermochelys coriacea), the Lesothan succulent Aloe polyphylla, and most other species in decline. Relic species generally face an overwhelming web of threats that are impossible to disentangle.
Further complicating the picture are two meta-disturbances: global climate change and economic globalization. Climate change will make many areas inhospitable to their present inhabitants. Entire biotic communities will be evicted: coastal wetlands will be permanently submerged, many cloud forests will dry out, some dry savannas will become lush while others become deserts. Studies suggest that the types of climate shifts we can expect over the next century are well within the experiential history of most species that have survived the last two million years. In the past, most could have moved to new regions. But today only weedy species have the capacity to migrate and reestablish thriving populations in new habitats, which invariably are human-disturbed areas. For the rest, there is either no place to go because acceptable habitat has been reduced to a few isolated patches surrounded by a sea of human development. There is no way for non-weedy species to get to potentially more suitable locations (if they exist) hundreds of miles away because of interposed cities, roadways, subdivisions, shopping centers, and airports.
Economic globalization exacerbates the species-loss problem in several ways. Globalization increases the demand for natural resources in remote and undeveloped regions. In locations previously occupied by subsistence villages, labor towns spring up to support foreign timber and mining operations. As foreign capital flows into undeveloped regions it inflates the price paid for local goods, thereby increasing incentives for over-exploitation to feed the lucrative export market. Timber from the Malaysian and Indonesian rainforests bought and paid for by Japanese firms brings a much higher return than the same lumber sold in local markets. Over 80 percent of these rainforests have now been logged, with the consequence that the orangutan population is now less than ten percent of what it was decades ago.
Perhaps most importantly, the booming trade of the globalized economy accelerates the pace of alien species being transported around the globe. Breaking down economic barriers effectively breaks down geographic, ecological, and biotic barriers as vast numbers of plants and animals are shipped worldwide to support the pet and horticultural trades. Although presently only about five percent of these aliens take hold and flourish in their new environs, five percent of an exploding number is itself a large number. (As a reference point, 25 percent of the vascular plants in the United States today are alien species.)
Unintended introductions of alien plants, animals, and other organisms are even more threatening since authorities make no attempt to screen out truly harmful organisms. Alien pests, parasites, and predators take an increasingly high toll on native ecosystems. As ships and planes shuttle between continents carrying unprecedented volumes of cargo, they cart with them a growing roster of stow-away organisms. The Asian long-horn beetle (Anoplophora glabripennis), for example, invaded the United States in 1996 encased in wood crates from China or Korea. Spreading through New York and Chicago, they decimated local trees, especially maples. Since then, adult beetles have been intercepted at 17 U.S. ports.
Thus, climate change and economic globalization are powerful agents of human selection that amplify and make irreversible the traditional and localized human disturbances that undermine biodiversity.
Why There Is Nothing We Can Do
As our awareness of the extinction crisis has grown, we have taken some ameliorative actions. In the United States we have imposed rules upon ourselves to try to halt the loss. The U.S. Endangered Species Act prohibits the taking, harm, or harassment of some 1,300 plants and animals designated by the U.S. Fish and Wildlife Service. Some critical habitats of these species are also protected. In addition, 44 of the 50 states have some form of state-level endangered species act of their own, through which they try to protect locally threatened species.
Since the early 1990s the European Union has had its Habitat Directive, which makes it illegal to kill or harm about 700 protected species or to disrupt 168 specially designated habitats. Approaching the problem from a different angle is the Convention on the International Trade of Endangered Species (CITES), which, as the name implies, is an attempt by the international community-presently over 150 countries-to limit the global trade in threatened species. About 30,000 plants and animals are on the CITES list. Thousands of species are added annually.
Meanwhile, nations, acting individually and through international conventions, have attempted to set aside biologically valuable landscapes and ocean areas as wildlife refuges and bioreserves. More than ten percent of the earth now has some form of protected status. The Parsa Reserve in Nepal covers about 500 square kilometers and offers sanctuary to a range of creatures, including 300 species of birds. The Northwestern Hawaiian Islands Coral Reef Ecosystem Reserve, encompassing over 400,000 square kilometers of ocean, protects about 70 percent of the coral reef ecosystems in the United States. Over 7,000 marine species are associated with this area, of which 25 percent are found nowhere else on the planet.
Recognizing that governments have limited political and fiscal resources, nongovernmental organizations have moved to impede the flow of species loss through land protection, public education, litigation, and policy advocacy. The Nature Conservancy claims to have helped to preserve over 117 million acres of wildlife habitat over the past 50-plus years. In the United States the Center for Biological Diversity, Defenders of Wildlife, and others use the courts to force recalcitrant government agencies to implement and enforce existing conservation laws and regulations.
A casual reading of the news would suggest these efforts are paying off:
By 1939 the number of whooping cranes (Grus americana) in the United States had declined to 18. Thanks to captive breeding, today there are over 300 whooping cranes, with 180 living in the wild. In an astounding effort, humans piloting ultralight aircraft taught a novice flock how to migrate from Florida to Wisconsin.
The population of Puerto Rican crested toads (Peltophryne lemur) has tripled to 300 over the past 25 years thanks to captive breeding in U.S. zoos and restocking in the wild.
A recent survey of tigers in India's Sunderbans Forest suggests that the preserve's population is stable and may even reflect an increase in cubs.
The last remaining patch of Kneeland prairie penny-cress (Thlaspi californicum), found in only one California county, will be saved with a ten-year, $300,000 conservation effort.
Perhaps if we dedicated a few billion dollars more, increased cooperative efforts among governments, expanded the system of bioreserves walling off biodiversity hot spots, cultivated sustainable economics among local communities, and reduced human consumption habits we could save the earth's biota.
Unfortunately, such efforts are far too little and far, far too late. In fact these and similar apparent success stories reflect a much more insidious process that is reshaping the living earth. Our most common tools for preserving biodiversity?prohibitory laws and regulations, bioreserves, and sustainable-development programs?are themselves powerful engines of human selection, tweaking (for our pleasure) but not fundamentally altering the outcome: massive species loss...