LIKE ANY harassed executive whose in-tray overflows with projects, Russell Mittermeier has too many options and too little time and money to see them through. But Mittermeier, the president of Conservation International in Washington DC, is not just choosing whether to build laser gizmos or turbo-CD-ROM-widgets. The fate of hundreds, perhaps thousands of the world鈥檚 endangered species hangs on the decisions he helps to make. For example, which is more important: a nature reserve to protect wild asses in Somalia, or one to protect lemurs in Madagascar? Should international donors back a Brazilian national park in the western Amazon, or in the Atlantic coastal forest?
To meet the conservation needs in developing countries alone would cost nearly $17 billion a year, according to a 1991 estimate by the IUCN (the World Conservation Union), the UN Environment Programme and the World Wide Fund for Nature. Present levels of spending probably provide no more than a quarter of that sum, says Walter Reid, vice-president of the World Resources Institute in Washington DC. To make the most of the scarce resources they have, conservation planners need clear, well-justified priorities. But setting these priorities is far from straightforward.
Many priority setters elect to preserve as many endangered species as possible by concentrating their efforts on biodiversity 鈥渉ot spots鈥 such as the Amazon rainforest. A growing number, however, are opting for a newer strategy of building a balanced portfolio of nature reserves that includes representatives of every major type of habitat, even if that ultimately means saving fewer endangered species in total.
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The fate of either approach could depend on the answers to two fundamental questions: how do you define 鈥渆ndangered鈥, and are some species more valuable than others? In both cases, conservationists have been re-thinking the criteria they use.
When endangered species became a front-burner issue in the 1960s and 1970s, policy makers adopted vague, almost circular definitions of the term. The IUCN, which publishes the Red Data Books that list endangered species, defined endangered species as those 鈥渋n danger of extinction and whose survival is unlikely if the causal factors continue operating鈥. The Convention on International Trade in Endangered Species (CITES) used similar wording for its highest category of concern. In the decades since, many biologists have grown uncomfortable with these definitions, fearing that they allow too much room for political expediency and whim.
Biologists agree in principle on the red flags that signal that a species faces impending extinction. First, species with only one or two surviving populations have all their ecological eggs in one basket and so could be wiped out by a single stroke of bad luck such as a drought or a disease. Second, those with too few individuals will not have the genetic resources to cope with an ever-changing world. And third, plummeting numbers of any species 鈥 no matter how common 鈥 must mean that something is seriously amiss. But are three rookeries of a penguin species enough to guarantee its survival? How few is 鈥渢oo few鈥 elephants? And how far, and how fast, do the numbers of a certain cactus have to fall before we ought to worry?
Rule of thumb
Some conservation biologists say there are no general answers to questions like these, because every species occupies a unique ecological setting. 鈥淭here鈥檚 no short cut,鈥 says Daniel Simberloff, a conservation biologist at Florida State University in Tallahassee. When it comes to assessing the risk of extinction, 鈥測ou really need about a doctoral dissertation鈥檚 worth of research on a species to make a reasonable estimate鈥, he says.
But in a world inhabited by unknown millions of species, thousands of which are already in peril, there simply are not enough doctoral students to go around. Policy makers need rules of thumb, even imperfect ones, says Georgina Mace, a research fellow at the Zoological Society of London. Attempting to draw up such guidelines in conservation is no more arbitrary than setting income limits for public assistance programmes, she says. 鈥淓veryone accepts that for practical reasons and reasons of equality you have to have those rules. For some reason, it seems to be much more controversial in biology.鈥
Last year an IUCN panel headed by Mace and Simon Stuart of IUCN completed a five-year effort to set crisp, numerical criteria by which species might be considered, in increasing order of threat, 鈥渧ulnerable鈥, 鈥渆ndangered鈥 or 鈥渃ritical鈥. The criteria it set are complex, reflecting the multiplicity of danger signs. For a species to be rated as 鈥渆ndangered鈥, for example, fewer than 250 individuals must survive, by the best available estimate; or fewer than 2500 mature individuals if they occur in a single population or their numbers are dwindling or expected to. Species also qualify as 鈥渆ndangered鈥 if their numbers have declined by more than 50 per cent in the past 10 years or 3 generations, whichever is longer. So too do species that occupy less than 500 square kilometres of habitat and show other signs of trouble, such as declining, fragmented or wildly fluctuating populations.
In November 1994, the member nations of CITES unanimously adopted a similar set of criteria, although the numerical thresholds were relegated to a footnote to satisfy critics who felt that any single set of numbers could not apply to every species. These new, more precise criteria may cool the political battles over some of CITES鈥 more controversial decisions, and put any debate on a more scientific footing. 鈥淭he quantitative criteria make it more difficult to argue that black is white, and a more scientific debate has to take place than the normal screams and howls,鈥 says Stuart. At the same CITES conference, for example, several Central American countries argued vehemently that American big-leaf mahogany is a threatened species, while several South American countries maintained just as passionately that it is not. If delegates could have referred to an objective, unambiguous set of criteria, the debate might have generated less heat and more light, several participants said later.
To test the new IUCN criteria, Mace and her colleagues asked endangered-species specialists to generate lists of endangered vertebrates and some plants, then compared these with old lists drawn up using IUCN鈥檚 more subjective measures. 鈥淚n every place we鈥檝e used them, the consequence of applying the [new] criteria is that more species have been listed 鈥 usually only two to ten per cent more,鈥 says Mace. The new system, she says, seems more likely to include very rare but widespread species. However, locally abundant species with very restricted ranges seem less likely to be rated as endangered 鈥 a possible shortcoming of the new criteria.
First steps
But drawing up lists of endangered species is only half the battle, says Mace. 鈥淚 see listing as being the first, inclusive step. You make sure that that step, while being relatively rigorous, includes as many species as you would reasonably want.鈥 The next step is to decide how much time and effort to devote to each of the deserving species. 鈥淭hat鈥檚 a more exclusive activity,鈥 she says. 鈥淵ou need to be more precise about what it is you鈥檙e trying to maximise.鈥 For example, should conservationists simply try to save as many species as possible, starting with the most highly endangered, or are certain species in some sense more worth saving than others?
On ethical grounds, at any rate, many conservation biologists maintain that every species has an equal right to survive, and that humans have no right to favour one over another. Others argue that larger, more intelligent animals have a stronger claim on humans鈥 interest and loyalty. 鈥淚 cannot accord a planarian or a copepod the same sort of value I accord an elephant or a gorilla,鈥 says William Conway, general director of the Wildlife Conservation Society in New York City. Larger animals often play more important ecological roles, he adds. For example, by trampling and feeding on vegetation, elephants help maintain the open woodlands used by many other species. But not every important species is large, says Conway. Ants, termites and pollinating insects can also play key roles in their ecosystems and are equally deserving of attention.
Sometimes, too, a species may be singled out for its evolutionary importance. The tailed frog of western North America, for example, is the only surviving member of an entire branch of the frog evolutionary tree, having diverged from its cousins some 150 million years ago. The extinction of this frog would leave a bigger hole than would pruning a mere twig of a species or subspecies with many close relatives.
Finally, many scientists argue that large, glamorous animals such as tigers or spotted owls deserve special attention because conservation efforts directed at 鈥渇lagship鈥 species often rescue a whole flotilla of smaller species in their wake. 鈥淵ou鈥檙e looking for multiplier effects,鈥 says John Robinson, director of international conservation programmes at the Wildlife Conservation Society. 鈥淚f you protect a significant population of tigers, you鈥檙e going to have to protect a significant chunk of dry forest in India, and that鈥檚 also important.
Survival strategy
But deciding which species are in danger will not do any good unless conservationists can also work out a strategy to help them survive. Apart from the specialised subdiscipline of captive breeding 鈥 restricted to a tiny fraction of the world鈥檚 threatened species by limits on time, money and the capacity of the world鈥檚 zoos 鈥 most conservation programmes protect whole habitats, not individual species. Many conservationists maintain that the ecosystems themselves, not their component species, should be the paramount goal of their efforts. After all, says Robinson, 鈥渋f we were only interested in preserving the tiger, we would breed them in zoos. But we鈥檙e really interested in preserving that whole wild area in which the tiger lives.鈥
Conserving habitats rather than individual species offers several advantages. When a government sets aside a block of habitat as a park or reserve, it preserves every thing in it 鈥 even obscure organisms that scientists have yet to identify and name, let alone count.
Habitat loss is the single factor most likely to push an imperilled species over the edge, so saving habitats is at the heart of conservation. A habitat-centred approach also offers conservationists the opportunity to act early, catching species before they teeter at the brink of extinction. Such an approach substitutes preventive medicine for conservation鈥檚 conventional 鈥渃asualty department鈥 strategy. And like patients in casualty, species that show up on endangered lists may already be beyond saving.
Over the past decade, many conservation organisations have begun focusing on habitats, but the same nagging question pops up here too: how do you decide which habitats should be given the highest conservation priority? Conservation planners usually aim their efforts at 鈥渂iodiversity hot spots鈥 鈥 those habitats and countries with the greatest diversity or the most endangered species 鈥 with the goal of saving the most species per unit of effort. For example, Conservation International recognises 15 tropical rainforest hot spots, including Madagascar, Indonesia, the eastern slopes of the Andes and the Atlantic forest of Brazil. Although the 15 hot spots together occupy only 4 per cent of the Earth鈥檚 land surface, they contain an estimated 30 to 40 per cent of all terrestrial species and more than their share of the world鈥檚 endangered species.
Hot spots could be ranked not only by the number of species present, but also by their evolutionary uniqueness. Using this approach, a computer program called Worldmap, developed at the Natural History Museum in London, assembles data on the distributions of plants and animals, weights each species according to its evolutionary uniqueness, and then selects hot spots where the sum of these values is greatest. After each reserve has been set aside, Worldmap recalculates priorities such that the next choice avoids duplicating the species already protected.
A second, and newer, approach to habitat conservation uses the metaphor of Noah鈥檚 Ark. Unlike the Biblical ark, however, which Noah stocked with individual species, planners will fill the new ark with ecosystems. As Kent Redford, director of conservation science and stewardship of the Latin American division of the conservation organisation Nature Conservancy, points out: 鈥淚f one were to imagine the next 鈥榞reat flood鈥, when you offload that ark there ought to be something that goes to every part of the world and serves as the seed for re-integrating that area ecologically. Under many of the current paradigms that drive priority-setting, you鈥檇 have this rich tropical rainforest, and the rest would still be mud, because you hadn鈥檛 saved any of it.鈥
In other words, the ark strategy calls for conservation planners to spread their efforts across all the major habitat types, no matter how rich or poor in species diversity, and no matter how common or rare their constituent species. 鈥淭he axiom of this argument is that you cannot compare across habitat types. You cannot say that a rainforest is more important than a desert,鈥 says Redford.
The ark strategy got a high-profile road test last September at a workshop in Miami to develop conservation priorities for Latin America and the Caribbean. Latin American experts and representatives of major international conservation organisations divided the continent, which has seven major habitat types, into 35 regions. Then participants prioritised these regions according to biological importance, degree of threat and the likelihood that conservation activities succeed. However, they only compared regions with the same habitat type, comparing like with like. In this way, for example, grasslands and deserts did not have to compete for attention with rainforests. 鈥淚t鈥檚 clear you want to be most concerned about high biological value and critical threat,鈥 says Redford. 鈥淏ut after that you have to start making really subjective decisions about whether it鈥檚 more important to work in areas that have less biological value but are highly threatened, or in areas with high biological value that are less threatened.鈥
By treating dry forests, grasslands and deserts as important in their own right, the workshop gave the drier ecosystems of southern South America high priority rankings for the first time. Bringing these ecosystems out from under the shadow of tropical rainforests helped redress an old slight, says Redford. 鈥淯ntil recently, people said, 鈥榯here is no biodiversity there鈥 which is just absurd,鈥 he says. 鈥淭he Pampas region is arguably the most threatened ecosystem on the whole continent, equivalent to the prairies in the US 鈥 tiny little pieces left on private holdings. And most people don鈥檛 even think of it.鈥
New order
Paradoxically, the strategy of preserving a 鈥減ortfolio鈥 of different habitat types suggests that conservationists should spend at least some of their time and money on habitats such as the boreal forest of Canada, which is in little danger of eradication. Though critics might argue that giving high priority to such conservation efforts merely wastes scarce resources that could have saved truly threatened species elsewhere, Redford prefers to think of it as preventive medicine. 鈥淒o you want to keep healthy people healthy, or do you only want to treat sick people? The current thinking is like saying that I want to devote all my resources to emergency rooms 鈥 You need to worry about those boreal forests before they turn into prairies.鈥
By distributing their priorities more broadly, conservationists may also be able to tap into new sources of funding, says Mittermeier. For example, now that Chile鈥檚 forests have emerged as a top priority, the Chilean government may devote more money to their conservation. Likewise, South Africa has no rainforests, but the Cape flora is the most diverse Mediterranean-like ecosystem on the planet. 鈥淭he more recognition you can get for that, the more likely South Africa will pay attention to it themselves. And they have money,鈥 says Mittermeier.
The new balanced portfolio strategy is just a few years old. It remains to be seen how well it will work in practice. But one thing seems certain. Regardless of how conservationists set their priorities, a lot of hard, detailed work lies ahead. 鈥淵ou know, there鈥檚 no way to win a conservation battle,鈥 says Conway. 鈥淵ou can only lose one, because the battle continues. The secret 鈥 and the price 鈥 of successful conservation is going to be constant innovation, constantly finding new solutions to new problems.鈥