The United Nations has made 2010 its . While there could be as many as 30 million species on this teeming planet, so far fewer than 2 million have been identified. That includes a staggering 114,000 catalogued in the past three years alone. Our exploration of life is just beginning. No wonder the UN is keen that this year should be one of celebration.
It is also time to take stock, though. Human activities are causing a mass extinction, but the right action now could pull life back from the brink. At last we are beginning to understand what generates biodiversity (Why the tropics are hotbeds of evolution) and what makes a good conservation programme (How to save an island). We can also predict how our activities today will shape biodiversity in the future (this article, below). It is a sobering vision – but one that is still in our power to change.
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Editorial: Let’s put an end to biosentimentality
A 3-metre-tall kangaroo; the car-sized armadillos called glyptodons; giant lemurs and elephant birds from Madagascar. Almost as soon as humans evolved, we began killing off other species, not just by hunting but also by changing the landscape with fire.
Now we are altering the planet more rapidly and profoundly than ever, and much of the diversity produced by half a billion years of evolution could be lost in the next few centuries. We are triggering a mass extinction that could be as severe as the one that ended the reign of the dinosaurs.
Given enough time, biodiversity will recover. Extinctions create new evolutionary opportunities for the survivors: the blossoming of mammals after the dinosaurs died out ultimately led to our evolution, after all. But the aftermath of this Anthropocene extinction will not be like any other. Humans have become the main driving force in evolution – and life will never be the same again.
The list of threats we pose to biodiversity is long. We are killing many creatures directly, destroying habitats, introducing exotic predators and diseases, and pumping out pollution. Already, a tenth of birds, a fifth of mammals and a third of amphibians are regarded as threatened.
Rapid climate change will make matters even worse. Warming threatens a lot of species that might otherwise be able to cope with the changes inflicted by humans, says Chris Thomas at the University of York in the UK. To work out how many species are at risk, Thomas and colleagues looked at the climatic conditions required by 1000 representative species and used them to work out how much habitable area would remain for each if the world warmed by between 1.5 and 2.5 °C. Based on these figures, the team estimated that between 15 and 37 per cent of species will be “committed to extinction” by 2050 ().
“There are very large uncertainties,” Thomas admits. “But it is equally likely for things to be worse than we are suggesting.” Indeed, without drastic action the world will . “We [will be] subjecting our biota to environmental conditions not seen for more than 10 million years,” Thomas says.
The combination of so many different challenges will make it increasingly difficult for species to cope. “It’s this perfect storm of extinction drivers that’s the problem,” says David Jablonski of the University of Chicago.
Loss of diversity is not just the result of these challenges, it is also part of the problem. Plummeting population levels have already greatly reduced the genetic diversity within many species, decreasing their chances of adapting to changing environments by depriving them of the raw material needed for evolution. As well as this, extinctions can lead to further extinctions, because so many species depend on others. And as ecosystems become less diverse, they generally become less resilient to change. “The worse it gets, the worse it gets,” says Jablonski.
The collapse of ecosystems will have huge economic consequences. From flooding in Haiti to dust storms in Beijing, the effects of environmental degradation are already hitting us hard. The loss of more coral reefs, for instance, would be a disaster for many fisheries and tourist resorts, and their death and erosion will leave formerly protected coastlines vulnerable to the ocean.
Dawn of the minifauna
Some believe there is still time to stave off the worst. “The level of extinction can be considerably modified,” says David Western of the African Conservation Centre in Nairobi, Kenya. For example, we must restore animals’ freedom to move, as the current strategy of trying to protect areas of high biodiversity will not work if species are trapped in increasingly unsuitable climate zones. Transporting species to areas that have a more suitable climate is also an option, although this would be expensive so could only be used for a few species.
Other researchers are more pessimistic. “We can turn the ship a little,” says Jablonski. The main problem he sees is a lack of political will.
No one can predict exactly what the Earth of our descendants will look like. However, there are some clues in what’s happening right now. Our influence is so profound that we are altering the evolutionary pressures that shape life. There have already been very large and quick behavioural changes as landscapes become “humanscapes”, says Western. Foxes and coyotes are adapting to life in cities, and elephants have started moving out of parks at night to feed at the fringes of settlements before returning in the morning to avoid us. Human pressures are also producing genetic changes in wildlife. As a result of poaching for ivory, for instance, tuskless elephants are evolving. “There will be a new round of evolution,” says Western. “We are already seeing that.”
Almost all biologists believe that the age of megafauna is over. Large, slow-to-reproduce animals are the most likely to become extinct and, at least on land, those that do survive will not have the vast expanses of habitat needed for further speciation. The greater pressures on large animals will downsize entire communities, says Western. For example, small antelope are likely to become more common than larger herbivores on the African savannah, which would lead to lions becoming smaller too. Lions may also become more benign as we kill off the aggressive individuals that encroach on human settlements. “There will be a transformation of large animals to ones that are compatible with the humanscape,” Western says.
The species most likely to thrive will be small ones that are easily spread around by humans and good at colonising new territory – pests, weeds and pathogens. “It’s not good to be big or rare,” says Jablonski. “You want to be a rat, or a weed, or a cockroach.” In theory, as humans fragment habitats, evolution may throw up new species, especially small mammals and insects – but these might not be very resilient. They may limp along and easily go extinct, Jablonski says.
So the ecosystems of the future are likely to be far poorer affairs, with fewer species, fewer links between species and a dearth of large animals. Anyone who has dived on a degraded reef knows the sort of thing to expect: a dazzling array of corals swarming with fish of all shapes and sizes giving way to algae-covered rocks with barely a tiddler in sight.
After previous mass extinctions, the recovery of biodiversity took millions of years. Coral reefs, for example, did not reappear until about 10 million years after the Permian-Triassic extinction (see diagram). The recovery from the Anthropocene extinction could be different, however, as we are already laying the foundations that will allow our descendants to speed up the process.
“The recovery from the Anthropocene extinction could be far faster than previous mass extinctions”
For starters, we are preserving samples of endangered species so that they can be revived if necessary. There are over 1400 plant “gene banks” worldwide storing millions of seeds, mostly from food plants but also some wild species. Animals are also being stored as frozen tissue samples. The at San Diego Zoo in California contains over 8000 samples from 800 species or subspecies, and many similar projects are being set up around the world.
Even assuming that civilisation survives and that gene banks get the funding they need to store many more samples, to look after them for the next few centuries and to revive species as suitable habitat becomes available, only a tiny fraction of the world’s species could be saved this way. Nevertheless, that fraction could include not only many charismatic megafauna – revived by cloning, perhaps – but also keystone species that play a vital role in maintaining ecosystems, such as corals. The Zoological Society of London is considering creating a “cryobank” of frozen corals, which can be revived simply by thawing them.
The second thing people could do to aid the recovery of biodiversity would be to manage habitats in a way that allows evolution to continue. This is now being tried in the Cape region of South Africa, home to some of the most diverse flora in the world. “Species come and species go,” says Richard Cowling of the Nelson Mandela Metropolitan University, Port Elizabeth. “You’ve got to preserve the processes.”
To that end, Cowling has helped to devise a conservation plan for the region that focuses not only on preserving distinct kinds of habitats, but also the gradients between them, such as between soil types and micro-climates (). The idea is that environmental gradients produce genetic gradients within species as subpopulations adapt to local conditions. The resulting diversity can give rise to new species if, say, the populations at the extreme ends of the gradient become isolated.
In the future, ecologists might go even further and actively manage ecosystems in a way that promotes evolutionary processes that produce biodiversity. “It’s a damn good idea,” says Cowling.
Finally, we might generate diversity in an even more direct way. We have already created millions of new varieties of plants and animals through selective breeding, and many of these creatures, from mustangs and burros to the dingo, have established feral populations. In the vacuum left by a mass extinction, many more domesticated species may turn wild – and genetically modified domesticates could have a particularly dramatic impact.
Take the increasing interest in boosting the efficiency of photosynthesis to increase food production. Most plants capture less than 2 per cent of available energy. If this proportion can be significantly increased, the resulting “superphotosynthesisers” might outcompete many wild plants over the next few millennia, compounding biodiversity loss. On a geological timescale, however, they could lead to unprecedented levels of diversity, because more energy would be available to life than ever before.
Things might get wilder still if we create artificial life. Some researchers are trying to produce truly synthetic organisms whose chemistry is unlike anything alive today. It is unlikely that such organisms could survive outside laboratories, as they would have to compete with species honed by billions of years of evolution, but it might just happen.
This vision of a world in which biodiversity depends largely on clones of long-extinct creatures, feral animals, genetically modified organisms, human-directed evolution and perhaps even artificial life will sound like a nightmare to many people. But it is just a continuation of the process that began as soon as our ancestors started reshaping the landscape and meddling with evolution. And if we don’t do more about the accelerating rate of extinctions, it is perhaps the best outcome our descendants can hope for.
Read more:
Living world: Why the tropics are hotbeds of evolution
Living world: How to save an island
Living world: Five species that cheated extinction
Editorial: Let’s put an end to biosentimentality
