The planet is in the middle of an extinction crisis, the sixth great wave in its history. But unlike major extinction events of the past like the Permian-Triassic event 250 million years ago, in which 70% of all terrestrial species were wiped out, probably because of an asteroid impact or a similar natural disaster this time human beings are the cause. Hard numbers are difficult to find, but many scientists believe Earth's species are going extinct at a rate that is up to 1,000 times higher than before human beings came on the scene.
Meanwhile, human beings have also been working to counteract the effects of their development and growth as well as man-made climate change. Measures like the U.S. Endangered Species Act, habitat-protecting nature reserves and hunting prohibitions are all designed to slow the rate of extinction and preserve dwindling species. But a new paper in the journal Biological Conservation says we may not be trying hard enough. A team of Australian researchers led by environmental scientist Lochran Traill finds that current conservation policy tends to underestimate the number of individuals needed in a population of endangered species to keep it viable. In the face of environmental fluctuation and potential disasters, says Traill, we need animal populations to number in the thousands for survival not in the hundreds, which is what most conservationists aim for.
It's not hard to understand Traill's logic the smaller a species population becomes, the more vulnerable it is to extinction. Not only are small, dispersed populations more easily wiped out, but also they are more susceptible to inbreeding, which leads to a decrease in genetic diversity and further pushes the species toward extinction. So the goal is to boost species' numbers, and the long-standing rule for such conservation is 50/500 meaning that 50 adults in a population are required to avoid the risks of inbreeding, and 500 are needed to avoid extinction due to sudden environmental change.
But Traill and his colleagues, after reviewing the most current data, found that a better rule would be 5,000 meaning no fewer than 5,000 adult individuals are needed to keep a species safe from the threat of extinction. Dip below that level, and any sudden change the loss of a valued habitat, a new disease could wipe out a species before conservationists would have time to act. "Small populations have therefore reached a point of departure: away from the ability to adapt to changing environmental circumstances and toward inflexible vulnerability to those same changes," writes Traill.
Increasing species numbers, however, may not be possible. The main hurdle, not surprisingly, is politics. The needs of a real conservation effort may require a level of animal protection beyond what is politically possible. That puts conservationists in a bind. Do they push for the tighter levels of protection that might successfully preserve endangered species or do they accept what is politically feasible? "We suggest that most vulnerable species are not really being managed for viability," writes Traill. "Rather, conservation targets in most cases merely aim to maximize short-term [species] persistence and fit with complex political and financial realities."
Indeed, the political realities are sometimes dire. As American environmentalists discovered during former President George W. Bush's Administration, it was difficult enough to preserve existing levels of protection for wildlife, let alone push for tougher standards. Yet if Traill and his colleagues are right, the status quo is not enough to protect endangered species, and it's too weak to stop the sixth great extinction wave.
The conservationists' dilemma echoes that of many climate scientists. Do they push for the strict carbon-emissions reductions that many studies say are necessary to prevent serious global warming or do they accept weaker but more politically realistic targets? Whether it's conservation or climate change, science must often give way to statecraft.