SPOT DISTRIBUTION IN THE MEADOW BROWN BUTTERFLY, MANIOLA-JURTINA L (LEPIDOPTERA, SATYRIDAE) - SOUTH WELSH POPULATIONS

Meadow brown butterflies, M. jurtina, were studied on Skokholm Island, off the Pembrokeshire coast, from 1976-1978 and at 6 other sites in south Wales from 1973-1977. 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 the 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. The increasingly maritime climate and the fragmentation of habitat on the coastal fringes of the species range are factors which may selectively favor butterflies with high flying and dispersal ability. Brakefield (1983) has offered evidence that more highly spotted meadow browns indeed have such an ability.