If current trends continue, elephants, giraffes, and zebras could go extinct in the not-too-distant future.
Rodents teeming with parasites that carry black plague would fill the void, suggests ongoing research in Africa. If so, the threat to human health could prompt the tantalizingly feasible solution of de-extinction -- that is, resurrecting the big animals and releasing them back into the wild.
De-extinction for conservation purposes is a "matter of when, not if," said Philip Seddon, a zoologist at the University of Otaga in New Zealand. "We need to think very hard about which are the good candidate species."
The need for serious consideration of the idea stems from the reality that the world is in the throes of an extinction crisis and demands a re-think of wildlife conservation, he and other scientists argue in a series of papers and essays published Thursday in the journal Science.
Rodolfo Dirzo at Stanford University, who is conducting the rodent research in Africa, is hesitant when it comes to resurrecting extinct species, preferring instead to focus on slowing human population growth and its impact on the environment with the development of a "view that the well-being of natural ecosystems including the animals actually represents the well-being of humans as well."
But the case could be made, he said, to bring back a recently-extinct species if its habitat is intact and the local communities are on board with the idea. Even then, though, many scientific and ethical questions remain to be explored, he and other scientists said.
"In most cases, (de-extinction) is very much a distraction from the big issues of conservation, which are more and more looking closer and closer to how does sustainable development happen, how do we live effectively on this planet without just completely removing the wealth of biology that we depend on," said Joshua Tewksbury, director of the conservation organization WWF's Luc Hoffman Institute in Geneva and co-author of an essay on the crisis.
'Defaunation' of Earth
Since the year 1500, at least 322 vertebrate species have gone extinct such as the dodo. Across vertebrates, population abundance has declined by 28 percent over the past four decades with many local populations now extinct. Globally, populations of invertebrates –- insects such as beetles, butterflies, and spiders -- have decreased by 45 percent over the past 40 years.
"So profound is this problem that we have applied the term 'defaunation' to describe it," Dirzo and colleagues write in their review paper on the crisis. "This recent pulse of animal loss … is not only a conspicuous consequence of human impacts on the planet but also a primary driver of global environmental change in its own right."
Among the consequences of this wave of extinction are losses of ecosystem services vital to the well-being of humans, such as crop pollination, agricultural pest control, seed dispersal, decomposition and cycling of nutrients, water filtration, and the supply of chemical compounds that may prove essential for novel, life-saving pharmaceuticals.
"There are ecological, economic, and ethical consequences of those losses -– and this important paper documents them in considerable detail," Stuart Pimm, a conservation ecologist at Duke University in Durham, N.C., said in an email. He was not involved in the Science series.
Dirzo's research in Kenya indicates that as large animals such as elephants, giraffes, and zebras decline, grasses and shrubs grow taller and thicker, obscuring rodents from the view of predators and allowing their populations to expand. "In the absence of the big animals, you tend to double the number of rats," he said. The rats carry parasites that harbor a range of diseases, including black plague.
Moving species and de-extinction
Finding success in stemming extinction with traditional conservation measures such as protecting patches of wilderness and limiting hunting is "proving difficult," said Seddon, who is the lead author of a review paper that calls for an embrace of more intensive, and sometimes controversial, strategies such as translocation and even de-extinction.
At one end of what he calls the translocation spectrum is the movement of species from one place to another to augment an existing population with greater numbers or genetic diversity, for example.
Further along the spectrum are ideas such as reintroducing a species that has gone locally extinct, such as was done with wolves in the Northern Rockies. More controversial approaches include moving a species to a place it hasn't been before to avoid extinction from factors such as climate change or invasive species.
"The other end of that is when you say we want to move things not necessarily, or only, for that species but because we want to restore or increase the resilience of the whole ecosystem," Seddon said.
This last case, he explained, is known as ecological replacement. This has already been carried out, for example, on islands in the Indian Ocean where an exotic species of giant tortoise was released to restore the grazing and seed dispersal services that were lost when the local tortoise went extinct.
De-extinction, he said, could play a role within this translocation spectrum, especially as reintroduction to a native, intact habitat or as an ecological replacement.
But the concept is controversial. "There is a very real worry that if you feel that you can just bring anything back at any time you want you actually reduce the urgency of the issue," said WWF's Tewksbury. "And the issue isn't just around an individual species, but its value in a cultural context, its value in an ecosystem context, its value within an economic context."
According to Seddon, concerns about de-extinction warrant active and vigorous debate but "we've got to acknowledge it is on the horizon and figure out how to maximize the benefits for conservation."