The distribution and decline of a widespread butterfly Lycaena phlaeas in a pastoral landscape

1. Ecological specialists are often regarded as most likely to be threatene d by anthropogenic habitat changes but few relevant data are available on c hanges in the status of widespread species. 2. Grid square distribution maps have been used widely to measure rates of decline and target conservation resources but it is known that coarse grain mapping is not appropriate to identify declines in widespread species that initially contain numerous local populations per grid cell. Changes in the status of widespread species need to be quantified. 3. Present-day habitat associations, determined from over 2000 transect cou nts, combined with data on historical and present-day habitat distributions , reveal that the area of occupancy and population-level rate of decline of the Small Copper butterfly Lycaena phlaeas is likely to have been of the o rder of 92 and 89% respectively, in 35 km(2) of North Wales. Similar data o n the species' major host plants Rumex acetosa and R. acetosella indicate p ossible declines in area occupied of 48 and 91%. If a 1-km(2) grid was appl ied to the landscape, and if L. phlaeas, R. acetosa, and R. acetosella had occupied all 1-km(2) cells in the study area in 1901 (non-limestone cells f or R. acetosella only), their declines would only have been recorded as 15, 9, and 35% respectively. 4. Many declining ecological specialists are threatened with extinction bec ause of their initial rarity. At a population level, however, they may or m ay not be declining faster than less specialised species. The results prese nted here illustrate that some widespread species may have declined as much as many of Britain's rarities.