Commonness and rarity in British butterflies.

Commonness and rarity among British butterflies have been examined by relating features of biology and ecology to geographical distribution. No single attribute totally differentiates between common and rare species. However, several characteristics which are correlated with abundance appear likely to influence the capacity of species to exploit the artificial, disturbed and productive habitats which have been created by modern land-use and now occupy much of the landscape. Several features of geographical distribution, perhaps indicative of climatic tolerance are also correlated with abundance. Species of butterfly which are recorded from the greatest number of 10-km squares in England, Scotland and Wales are relatively large, form ‘open’ or migratory populations, exploit larval food plants of productive habitats, have rapidly maturing larvae, hibernate as a pupa or an amigo and extend into parts of NW Europe with relatively low summer temperatures. Two grouping of common butterflies are distinguished: (a) those which produce several broods per year, are polyphagous, utilize larval food plants of disturbed habitats and have a short-lived imago (Pieridae subfamily Pierinae); (b) single-brooded, monophagous species in which the imago is long-lived and the larvae exploit species of food plants of undisturbed habitats (Nymphalidale sub-family Nymphalini). By contrast, the rarest species of butterfly are variously large or small, tend to occur in ‘closed’ populations, produce a single brood per year, exploit larval food plants of unproductive habitats and produce long-lived larvae, with a life span exceeding that of the imago. Typically, these larvae feed on only one species or genus of food plant. Butterflies and higher plants appear to have exhibited a similar range of reactions to modern land-use; changes in the length and quality for food capture, development and reproduction provide a common explanation for these parallel responses. It is argued that the classification of butterflies will be useful as a prediction of the ecology and changing abundance of individual species and will assist in recognizing conservation priorities. The criteria used for butterflies are applicable to other major animal taxa, and provide a conceptual link to theories already applied to vascular plants. [ABSTRACT FROM AUTHOR]