Ecological correlates of island incidence and geographical range among British butterflies

The incidence of butterflies on British islands and their geographical (lat itudinal) ranges are regressed on ecological and life history variables. Th e objective has been to investigate the contribution of individual variable s and to incorporate information on phylogenetic links. The findings confir m the close relationship of species' incidence on islands with their geogra phical ranges on mainland Britain and that of species' geographical ranges with ecological variables, particularly migration capacity, hostplant type (variety) and breeding-habitat range. The results for island incidence cons idering phylogenetic links are virtually identical to those disregarding th em. For geographical range, the results are similar. The key variable in ea ch case is dispersal, scored in either one of two different ways. However, hostplant type takes precedence over breeding-habitat range when phylogenet ic links are considered. Species categorized for upper and lower quartiles for geographical range form isolated clusters in the first two axes of a pr incipal components analysis on a set of seven ecological variables. This re sult suggests the combined influence of a number of ecological variables on range size. Species with wide geographical ranges tend to have high migrat ion indices, a wide variety of hostplants and ubiquitous hostplants, long f light periods and are often multi-brooded; those with narrow geographical r anges tend to have low migration indices, sparse and limited hostplant reso urces, short flight periods and are often univoltine. A number of life hist ory variables are found to correlate significantly with geographical range, but account for only small amounts of variation. The lack of any associati on between range size and population abundance may well reflect the difficu lty of obtaining adequate measures for abundance. However, we caution again st expecting a strong correlation between range size and abundance.