Spot distribution in the meadow brown butterfly, Maniola jurtina L. (Lepidoptera: Satyridae): South Welsh populations

Meadow brown butterflies, Maniola jurtina , were studied on Skokholm Island, off the Pembrokeshire coast, from 1976 to 1978 and at six other sites in south Wales from 1973 to 1977.
Daily survival of butterflies on Skokholm was estimated by capture-recapture data to be 0.70–0.84, but these values may be low because in the year of detailed study, 1976, dispersal rates between study sites were high and increased through the emergence period.
The butterflies were scored for the number and placing of the hind wing spots (Ford, 1975). Female populations in the east of our study area resembled English populations for they were unimodal at 0 spots. Spotting increased westwards until on Skokholm and the adjacent mainland the females caught were roughly equally likely to have 0, 1 or 2 spots. The Skokholm male populations had many 3-spotted individuals and so the mode of 2 in the spot-frequency distribution was less clear cut that in English populations. The trends in south Wales therefore resemble those found along the Cornish peninsula and on the Isles of Scilly. We suggest the increasingly maritime climate and the fragmentation of habitat on the coastal fringes of the species range are factors which may selectively favour butterflies with high flying and dispersal ability. Brakefield (1983) has offered evidence that more highly spotted meadow browns indeed have such an ability.