Can butterflies keep cool in a warming world?
7 December 2012
Moving to new habitat could allow animals to cope as climate change makes their old haunts less suitable. But will this work in practice? Andrew Suggitt's work suggests there's no simple answer.
The difficulties that climate change can create for wildlife are well known. Many species will need to migrate substantial distances to higher ground or towards the poles in order to stay within their preferred temperature range.
Microclimates, or local variations in environmental conditions, present an intriguing idea: what if species could use this variation to find their required temperature niche in a warmer world? Such behaviour might allow species to adapt to climate change while remaining where they are, similar to the use of 'microrefugia' - small climatic refuges - when glaciers last covered much of the landscape. This could render migrations across hostile, human-modified landscapes unnecessary.
To test the idea, we used data from the wonderfully rigorous British and Catalan Butterfly Monitoring Schemes. In Britain and Catalonia, we had two study regions that were far enough apart to be independent tests of our hypothesis, but also close enough to share common species and habitat. The schemes involve dedicated volunteers walking transects of a few kilometres through butterfly-rich habitats every week, recording what they see. This gave us detailed information on which butterflies were in which habitats, and when. Combined with yearly climate information, this let us measure how the butterflies respond to changes in the climate.
So what did this hard work reveal? What came out was a mixed bag. Most species we tested responded as expected - that is, they used cooler habitats in warmer years, and vice versa. Three quarters of the species used cooler habitats in Catalonia than in Britain, confirming our hypothesis that the hotter the climate, the more likely species are to seek refuge in cool habitats like shady woodland. When comparing the annual differences to the regional ones, a similar proportion of the butterfly populations shifted habitat per unit of temperature change; another encouraging sign.
So far, so good. But - and there nearly always is a 'but' - these effects were small, in terms of the proportion of each population that was undertaking the shift. On average, only around 6-7 per cent of individuals were found in different habitats in response to the temperature difference between Britain and Catalonia.
Like most ecological analyses, a clear and precise prescription for conservation was elusive. The effect seemed to be widespread, but the butterflies' response wasn't enough to merit actions based solely upon it. We also couldn't tell what mechanism was responsible for the habitat shifting. Was it simply different rates of survival between the habitats? Was it genuine movement of individuals to preferred habitats? Or was it just a difference in the amount of time spent in each habitat?
These questions will likely be the subject of further work as we try to unpick how individuals use habitat at the local level. But thanks to the true commitment of hundreds of volunteers, we are at last beginning to understand how species' habitat associations might alter with climate change.
Dr Andrew Suggitt is a biologist at the University of York. Email: email@example.com
This work formed part of a NERC Ecology & Hydrology Funding Initiative project, 'The impact of climate change on habitat use: implications for predicting species' range changes.'
Adaptation & mitigation,
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