Can vulnerability among British bumblebee ( Bombus) species be explained by niche position and breadth?

Abstract

Comparison of the two flagship species of British bumblebee conservation ( Bombus distinguendus and B. sylvarum) with a widespread, common, and more stable species ( B. pascuorum) shows (1) that the two rarer and range-declining species in Britain had narrower (more specialized) climatic niches in western Europe even before their most severe declines, and (2) that the areas where they persist in Britain from 2000 onwards are closer climatically to the centres of their pre-decline west-European climatic niches than the areas from which they have been lost. Although data are available for few bumblebee species at present and further tests are needed, the first result supports earlier suggestions that it is bumblebee species with narrower climatic niches that are most vulnerable to decline. The second result supports the suggestion that it is in areas nearer the edges of their climatic niches where these species are most vulnerable to decline, although this can be ameliorated locally by higher food-resource levels. This is not to say that all patterns of bumblebee decline have been influenced by climatic niche, particularly in North America. Nonetheless, in Britain we find that even without climatic change, an interaction between climatic niche and food-plant reductions from land-use change retains the potential to explain at least some of the broader patterns of which species have declined, where they have declined, and how they have declined.