Winners of climate change?

The words 'climate change' tend to have negative, almost apocalyptic, connotations, we struggle to think on its positive effects (unless you live in the UK and you dream on Mediterranean weather to come, of course). Some species, however, thrive on warmer termeratures, so we could expect their distributions to be climate-limited and to increase their range north with increasing temperatures. This is true for many butterflies in the UK. In the first half of the twentieth century, many butterflies were restricted to the southern corner of the UK, whereas nowadays some are steadidly expanding into the north. Expanding butterflies include charismatic garden species such as the Comma, Polygonia c-album, the Speckled Wood, Pararge aegeria and the Holly Blue, Celastrina argiolus. Before the eighties they were absent from East Yorkshire and in the nineties these species become common north of the Humber. All good then? No, there is a problem: for a species to expand its range, suitable habitat needs to be present nearby - within the usual flying range of the species. Throughout the last century, with agriculture intensification, there was widespread loss of wild habitats in the UK. The combined effect of climate change and habitat loss was investigated in depth in a paper by Warren and co-workers. They used a dataset of 46 non-migrating butterfly species with northermost European ranges within the UK and detailed distribution records compiled in the last 40 years. Although all these species seem to develop faster and have denser populations in warmer temperatures (within UK limits) only a quarter of the species actually increased their range as predicted. Species increasing their range tended to be mobile habitat generalists: the species that are more likely to use gardens and other human-related habitats. Most habitat specialists, which tend to be more sedentary declined. This study illustrates the interplay of climate change and habitat availability: in our highly fragmented landscape, generalist, highly mobile species will be the winners of climate change, and we should be able to enjoy them more widely in our northern gardens, but biodiversity as a whole will, sadly, decline.

Comma

Speckled Wood

Holly Blue

Ringlet

Reference

Warren MS, Hill JK, Thomas JA, Asher J, Fox R, Huntley B, Roy DB, Telfer MG, Jeffcoate S, Harding P, Jeffcoate G, Willis SG, Greatorex-Davies JN, Moss D, & Thomas CD (2001). Rapid responses of British butterflies to opposing forces of climate and habitat change. Nature, 414 (6859), 65-9 PMID: 11689943