COMMONNESS AND RARITY IN BRITISH BUTTERFLIES

1. Commonness and rarity among British butterflies have been examined by relating features of biology and ecology to geographical distributi on. 2. No single attribute totally differentiates between common and r are species. However, several characteristics which are correlated wit h abundance appear likely to influence the capacity of species to expl oit the artificial, disturbed and productive habitats which have been created by modern land-use and now occupy much of the landscape. Sever al features of geographical distribution, perhaps indicative of climat ic tolerance are also correlated with abundance. 3. Species of butterf ly which are recorded from the greatest number of 10-km squares in Eng land, Scotland and Wales are relatively large, form 'open' or migrator y populations, exploit larval food plants of productive habitats, have rapidly maturing larvae, hibernate as a pupa or an imago and extend i nto parts of NW Europe with relatively low summer temperatures. 4. Two groupings of common butterflies are distinguished: (a) those which pr oduce several broods per year, are polyphagous, utilize larval food pl ants of disturbed habitats and have a short-lived imago (Pieridae subf amily Pierinae); (b) single-brooded, monophagous species in which the imago is long-lived and the larvae exploit species of food plants of u ndisturbed habitats (Nymphalidae subfamily Nymphalini). 5. By contrast , the rarest species of butterfly are variously large or small, tend t o occur in 'closed' populations, produce a single brood per year, expl oit larval food plants of unproductive habitats and produce long-lived larvae, with a life span exceeding that of the imago. Typically, thes e larvae feed on only one species or genus of food plant. 6. Butterfli es and higher plants appear to have exhibited a similar range of react ions to modern land-use; changes in the length and quality of opportun ities for food capture, development and reproduction provide a common explanation for these parallel responses. 7. It is argued that the cla ssification of butterflies will be useful as a prediction of the ecolo gy and changing abundance of individual species and will assist in rec ognizing conservation priorities. The criteria used for butterflies ar e applicable to other major animal taxa, and provide a conceptual link to theories already applied to vascular plants.