Relocation could help species cope with climate change
18 February 2009, by Tom Marshall
Human help with long-distance travel could help vulnerable species move into new areas, according to new research.
A marbled white butterfly like those used in the study.
Scientists looked at a concept called assisted colonisation, which involves moving animals to places that have recently become habitable to them because of climate change.
They found that butterflies moved to sites to the north of their traditional range have thrived in the years since and are spreading from the places they were originally released.
The idea is to maintain biodiversity by helping species adapt more quickly to a changing environment by moving into new areas than they would otherwise be able to.
'The success of the assisted colonisation demonstrates for the first time that moving species to areas identified as newly climatically-suitable can play a role in wildlife conservation,' says Professor Brian Huntley, an ecologist at the University of Durham and an author on the paper. 'This is likely to be especially important for rare species and for those that experience difficulty in crossing areas of unfavourable habitat.'
'The results show that although areas in the north are becoming suitable for a wider range of butterflies, shifts in butterfly distributions are lagging behind climate change because many species have limited mobility or struggle to cross large distances between sites offering suitable habitat,' he adds.
Many species have the northern edge of their European ranges somewhere in Britain. As the environment warms, new areas they could theoretically live in are appearing to the north of these former limits.
Barriers to butterfly movement
But many species haven't been able to take advantage of these opportunities to extend their range, because to get there they'd need to cross too much unfavourable terrain.
This is mostly because of the changes in land use that humans have made. Agricultural land devoted to single crops, roads and urban areas can all form barriers to progress even for relatively mobile creatures like butterflies.
Some animals can travel faster and further than others, but all need 'stepping stones' of favourable habitat along the way if they are to move long distances.
The team of researchers found that with a little help butterflies can survive and flourish beyond their northern ranges, in places they might not normally be able to reach.
A small skipper butterfly.
The scientists used climate models to identify areas in northern England where the effects of climate change mean that butterflies traditionally found in more southerly climes could now prosper.
In 1999 and 2000, they then caught Marbled White and Small Skipper butterflies in North Yorkshire and moved them to two of these sites in disused quarries in County Durham and Northumberland, well beyond the northern limits of their normal ranges.
The butterflies have thrived in their new environment. The Marbled White butterflies are easier to spot and hence more information is available on them; their population increased around fivefold between 2001 and 2006, and they have taken up residence in new areas of the quarries, spreading from the corners they were first introduced to.
Researchers at the Centre for Ecology & Hydrology (CEH) analysed the data from the UK Butterfly Monitoring Scheme (UKBMS), to look at how butterfly populations grow when they have naturally colonised a new site.
'The Marbled White butterfly has spread northward in recent decades as the climate has warmed, and a number of sites monitored by the UKBMS have been colonised,' says Dr David Roy at CEH, who worked on the project. 'We compared the growth of Marble White populations at colonised UKBMS sites with the increase in numbers at the introduced site, showing that the introduced population grew at a similar rate to other newly colonised sites,' he adds.
Apart from shedding light on the potential of assisted colonisation, the researchers say the work also shows the accuracy of the climate change models, and the value of long-term large-scale monitoring exercises like the UKBMS, in predicting where the butterflies would flourish.
Stepping stones to new habitats
Huntley says the researchers have now applied for a grant from the Natural Environment Research Council to do follow-up research on 'stepping stone' habitats. They want to find out more about questions like how big and close together these islands of wild habitat need to be in order to help different species move across the landscape.
Some species, like millipedes and snails, travel very slowly indeed but don't need much territory. Others, like birds and large mammals, can move much more quickly but need large areas of territory to feed them.
And smaller animals like butterflies may need to colonise a stepping stone area, establish a breeding population and move onto the next stepping stone in subsequent years. Bigger, faster animals may be able to use small stepping stone areas for temporary foraging before moving on after a few days, crossing large areas of countryside in a year.
Huntley says he envisages a landscape with small pockets of woodland, perhaps covering only a hectare or so, every kilometre. Larger pockets of forest would be planted at greater distances to provide for faster-moving animals that need more room; perhaps every hundred kilometres there could be a ten kilometre square of woodland.
'There are some species of butterfly for which a substantial hedge can be a barrier; others will move between patches of woodland that are kilometres apart,' he explains. 'For example the Speckled Wood butterfly lives on the Pennines, and we think it should be able to live on the Yorkshire Wolds as well. But it hasn't colonised the Wolds, because it has failed to cross the Vale of York, probably because it is so intensively farmed.'
Huntley adds that all species have some ability to cross the countryside, as shown by the way they moved into favourable habitats after the last ice age ended. 'Where I am in Durham was under an ice sheet 15,000 years ago,' he says. 'All the species that are here now somehow got here after the ice sheet melted, and that includes snails, millipedes and other slow-moving animals. They are all capable of doing this given time; the problem is how quickly climate change is now challenging them to move, and how many obstacles we have put in their way through changes in land use.'
The study appears in Conservation Letters. It was a collaboration between researchers at Durham University, the Universities of Leeds and York, the Centre for Ecology & Hydrology, and Butterfly Conservation.
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