SPATIAL SYNCHRONY AND ASYNCHRONY IN BUTTERFLY POPULATION-DYNAMICS

1. Data from Butterfly Monitoring Scheme (EMS) transect counts were us ed to investigate the decline in synchrony of population fluctuations with increasing distance between sample units, and to evaluate the rel ative effects of local and regional scale processes on population fluc tuations. 2. Each BMS transect is divided into sections and numbers (d ensities) of butterflies are recorded separately in each section. Loca l scale analyses examined population fluctuations on different section s within a single transect. Regional scale analyses examined fluctuati ons on different transects. 3. At the local scale population dynamics were found to be more closely synchronized between very close populati on units (sections) than more distant ones. There was considerable var iation between data sets but on average this correlation declined rela tively quickly over 1-2 km. 4. At the regional scale, where local envi ronmental heterogeneity was averaged out (sections were lumped togethe r within transect sites), the decline in synchrony with increasing dis tance (up to 200 km) was very small compared with local scale decrease , and populations remain partially synchronized throughout the range s tudied due to regionally correlated weather patterns. 5. Butterfly dis persal had a significant effect on synchrony at a local scale (several km): the dynamics of populations of relatively mobile species remaine d correlated over relatively long distances. At the regional level, ho wever, mobility was not a significant factor, implying that widespread environmental stochasticity is of over-riding importance at this scal e. 6. Although mobility and distance are significant factors in determ ining population synchrony/asynchrony, the low r(2) values attributabl e to them indicate that these factors are actually contributing relati vely little to the overall dynamics. Butterfly species show local vari ation in population dynamics, nested within broad scale synchrony whic h is presumably generated by the climate. Heterogeneity in population dynamics, in local environments, potentially aids metapopulation persi stence by buffering the effects of high levels of temporal environment al stochasticity.