Science & Environment

Climate swings increase extinction risk

American bullfrog
Image caption Species threatened by climate change can be relocated, but run the risk of becoming invasive, like the American bullfrog

Scientists have begun to predict the animals that may become extinct in the next century because of climate change.

Researchers at Brown University in the US have combined predictions of climate change with the geographic ranges of well-studied amphibians.

While the animals will try to migrate to areas with more suitable weather, short-term temperature fluctuations can cut them off.

The findings suggest more effort should be made to relocate vulnerable species.

It has been recognised for the past decade that the continuing future trend of global warming may drive species to permanently migrate in order to stay in an ideal habitat.

Amid concerns that this long-term migration may be disrupted by towns and cities, scientists at Brown University Dr Regan Early and Prof Dov Sax set out to predict the shifts in species' ranges over the next century.

Predictions of global climate change generally show warming trends, though both global annual oscillations and local climatic effects will play a role for given species.

The researchers combined these climate models with information on the ranges and tolerances of various species of frogs, toads and salamanders in the western US, with results that "really surprised", said Dr Early.

While they set out to find the disrupting effect of urban areas, they instead saw that the short-term climate fluctuations were enough to stop a species' migration in its tracks, cutting it off from ideal habitats and driving it to extinction.

They have published their results in the journal Ecology Letters.

Physical tolerance

Fifteen species of amphibians native to the western US were modelled in the study, as their ranges are well-known and their tolerances to physical extremes have been well-studied.

Image caption The California newt will struggle to migrate into a new habitat because of climate fluctuations

While none of these species is currently at risk, they predicted that over half of them would become extinct or endangered in the next 100 years due to these climate fluctuations.

Among the factors determining whether a species would survive were the speed at which it can migrate and its persistence, or robustness, in the face of climatic change.

For example, the models suggested that the Foothill Yellow-Legged frog would be able to make it into a new area, despite climate fluctuations, while the California newt would not fare so well in its migration across the Californian Central Valley.

Dr Early said: "This species isn't endangered now, and in the future there is more than enough suitable habitat for it to remain safe, but…the newt has a really hard time following its climate path to its future range because repeated climatic fluctuations cause it to retreat over and over again."

The tolerance of an animal to less-than-ideal climatic conditions will determine whether it can survive long enough to complete its migration.

"There is a lot of uncertainty in the ability of species to persist, and this is an under-appreciated factor," said Dr Early.

"For example, if an animal lives for a long time, it may fare better," she said. "If its eggs don't survive one year, being able to lay again the following year will increase the chances of survival."

Managed relocation

While the study was carried out on only a few species in a limited geographic range, the researchers are confident that the global climate fluctuations will drive similar patterns all around the world.

Small mammals, insects and plants are expected to react in a way similar to the amphibians, as they have similar tolerances to climate change; larger mammals may be less affected as their habitats are less climate-specific, the researchers believe.

Image caption Climate change could put the speckled black salamander into new areas beyond its current reach

The findings from this research are expected to add some clarity to discussions on whether to actively relocate species at risk from climate change.

There is concern over this "managed relocation" from conservation groups and governmental organisations, as the reactions of an ecosystem to the sudden introduction of a non-native species are poorly understood.

But research published in the journal Nature in 2004, which suggested that climate change-driven habitat loss could result in the extinction of 15-37% of all species, lends support to the idea of managed relocation as a way of maintaining biodiversity.

This new study from Dr Early and Prof Sax highlights the specific risks to species from climate fluctuations cutting off their migration paths.

"There are a lot of species that won't be able to take care of themselves," Prof Sax said. "We may instead need to consider using managed relocation more frequently than has been previously considered."

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