Document: JOR-3-82-41

Detecting population decline in widespread butterfly species.

LEON CORTES, J.L.* ¹, M.J.R.COWLEY ² and C.D.THOMAS ²

El Colegio de la Frontera Sur, Chiapas 29290 Mexico ¹
University of Leeds, Leeds LS2 9JT United Kingdom ²

Abstract:
Current fine population and habitat data, determined from over 2000 transect counts, combined with data on historical (1901) and present-day habitat distributions in a 35km² of fragmented North Wales, UK, reveal that the population-level decline of two widespread butterfly species (Polyommatus icarus and Lycaena phlaeas) are likely to be of the order of 75 and 89% respectively. Similar data on the butterflies' major host plants (Lotus corniculatus for P. icarus, and Rumex acetosa and R. acetosella for L. phlaeas) indicate possible declines in area occupied of 50, 48 and 91%. Based on 1km² grid maps, neither P. icarus and L. cornitulatus have been assessed as declining at all, and if L. phlaeas, R. acetosa, and R. acetosella had occupied all 1km² in the study area in 1901, their declines would only have been recorded as 15, 9, and 35% respectively. The results presented here suggest that apparently "common" widespread butterfly species may have declined as much as many of Britain's rarities: using present methods of assessment these declines are undetected.

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This abstract is being presented at: 3:15 PM in session:
Oral Session #53: Terrestrial Invertebrate Ecology.