Tamar Kahn
8 August 2007
Cape Town — Climate change is likely to give invasive species the edge over their indigenous counterparts, according to new research on tiny comma-like soil animals living on Marion Island in the southern Indian Ocean.
Scientists found that species of immigrant springtails that were inadvertently imported by visitors to the island over the past 70 years survived hot and dry conditions far better than those that had lived there for thousands of years.
The study is one of only a handful to date showing direct evidence that climate change threatens biodiversity. It is published online today by UK-based peer-review journal Proceedings of the Royal Society B: Biological Sciences.
"The real message here is that we are going to see some surprising synergies between climate change and alien invasion that will make it harder for us to manage our biodiversity," said the study's lead author, Prof Steven Chown, director of the Centre for Excellence in Invasion Biology at Stellenbosch University.
Marion Island has a cool, wet, windy environment that has already begun to experience the drought-like effects global climate change is expected to inflict on temperate regions. Over the past 50 years its annual mean temperature has risen by 1°C while its yearly precipitation has fallen by more than 500mm.
"That's the entire annual rainfall of the city of Pretoria," said Chown.
A team of South African and Norwegian scientists conducted a series of laboratory and field experiments on the six most abundant springtail species living on the island, exposing them to extra dry conditions at different temperatures.
In both sets of experiments they found the invasive species survived drought at high temperatures much better than their indigenous cousins, who fared better in cooler conditions.
"Our research shows climate change benefits invasive species because of the way they respond to the environment... we think the invasive springtails change their skin structure (to make them more resilient)," said Chown.
"Warm days on Marion Island are rare, so typically the (indigenous) animals don't show much flexibility. Invasives thrive because they do so well under a range of conditions," he said.
Springtails are one to two millimetres long, with a tiny spring under the tail that enables them to jump high in the air. They are one of the most abundant macroscopic animals on the planet, with up to tens of thousands per square metre of soil, and are found across the globe from Antarctica to the Arctic.
They played a crucial role in ecosystems, helping to recycle nutrients in the soil, said Chown. The scientists chose to study springtails on Marion Island because the history of the island's ecology has been extensively studied: for example, it had already been established that five of Marion Island's 16 springtail species were aliens introduced after a scientific research station was established on the island in 1947, said Chown.
"That kind of information is much harder to establish in SA," he said.
Sub-Antarctic Marion Island is home to SA's most far-flung weather station, 700km south of Cape Town. It is an important scientific research post.
Last year, scientists described Marion Island as the "canary in the coal mine", warning that changes there were a portent of things to come in similarly temperate regions, including parts of SA.
The springtail study supports their claim that hotter, drier conditions on the island are promoting the survival of a host of invasive species. Research on the island centres on efforts to understand weather systems and ecosystems
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