Changes in butterfly distributions

Background

Habitat degradation and climate change are altering the distribution and abundance of animals and plants throughout the world.

There is growing concern about increased rates of regional and global extinction. Are extinction rates for one group of organisms similar to those for others? Comprehensive surveys of plants, birds and butterflies have all been repeated in Britain over the past 20 to 45 years. These allow us for the first time to address the question of whether butterflies have declined as badly as birds or plants over similar time periods. They also allow us to examine the causes of change in butterfly distributions.

Methods

BRC has collaborated with the Botanical Society of the British Isles, Butterfly Conservation, British Trust for Ornithology, and the Universities of Leeds, York and Durham to address these questions. We evaluated changes in the distribution sizes and abundances of 46 species of butterflies that approach their northern climatic range margins in Britain. These insects might be expected to respond positively to climate warming. Results were compared with local population changes observed by the UK Butterfly Monitoring Scheme (UKBMS).

In a broader comparison, we compared distributional changes between the 1254 native species of vascular plants, 58 breeding butterfly species and 201 native breeding bird species.

Key results

Half of the species that were mobile and habitat generalists increased their distribution sizes over this period (consistent with climate change), whereas the other generalists and 89% of the habitat specialists declined in distribution size (consistent with habitat limitation).  Over the past 30 years, three-quarters of butterfly species with northern range margins declined: negative responses to habitat loss have outweighed positive responses to climate warming. The dual forces of habitat modification and climate change are likely to cause specialists to decline, leaving biological communities with reduced numbers of species and dominated by mobile and widespread habitat generalists.

When butterflies were compared with vascular plants and birds, butterflies experienced the greatest net losses, disappearing on average from 13% of their previously occupied 10-kilometre squares.

Most butterfly species declined.  We found that 28% of native plant species decreased in Britain over the past 40 years, 54% of native bird species decreased over 20 years, and 71% of butterflies decreased over ~20 years.

Other sources of information

Comparative analyses were published in Nature (Warren et al., 2001; Wilson et al., 2004) and Science (Thomas et al., 2004). The references are listed with other BRC publications on pp. 30-32.