Butterfly mobility

Abstract

Of the 55 species of butterfly which are resident within the British Isles, the majority have undergone changes in range (overall geographical occupation) and distribution (occurrence within range) within the past 150 years. Almost all have reduced distributions, but, more importantly, five species have become extinct and 18 have undergone major range contraction. In only eight species have there been consistent patterns of range expansion during the past 50 years (Pollard, 1991; Warren, 1992b). This general pattern of decline is matched in other areas of the Palaearctic (Kudrna, 1986; van Swaay, 1990). It is also the general trend for the Nearctic, where many formally common species are becoming increasingly scarce, especially in the region of the Atlantic and near Atlantic coast. These declines, which have been more rapid within the past 50 years than previously, are generally ascribed to the loss of habitat associated with changes of land use compounded by habitat fragmentation and isolation (Warren, 1992b). Other factors, such as climate change (Pratt, 1986) and pollution (Barbour, 1986a), may also be implicated but are less easily identified as causal factors. However, for those species which have recently expanded their range, or continue to do so — Anthocharis cardamines (orange tip), Ladoga Camilla (white admiral), Polygonia c-album (comma), Pararge aegeria (speckled wood) and Pyronia tithonus (gatekeeper) — habitat, and especially climate, have key roles in their range expansion (Pollard, 1979, 1991; Barbour, 1986b; Pratt, 1986; Pollard and Eversham, Chapter 2 this volume).