Spatial Synchrony and Asynchrony in Butterfly Population Dynamics

Abstract

1. Data from Butterfly Monitoring Scheme (BMS) transect counts were used to investigate the decline in synchrony of population fluctuations with increasing distance between sample units, and to evaluate the relative effects of local and regional scale processes on population fluctuations. 2. Each BMS transect is divided into sections and numbers (densities) of butterflies are recorded separately in each section. Local scale analyses examined population fluctuations on different sections within a single transect. Regional scale analyses examined fluctuations on different transects. 3. At the local scale population dynamics were found to be more closely synchronized between very close population units (sections) than more distant ones. There was considerable variation between data sets but on average this correlation declined relatively quickly over 1-2 km. 4. At the regional scale, where local environmental heterogeneity was averaged out (sections were lumped together within transect sites), the decline in synchrony with increasing distance (up to 200 km) was very small compared with local scale decrease, and populations remain partially synchronized throughout the range studied due to regionally correlated weather patterns. 5. Butterfly dispersal had a significant effect on synchrony at a local scale (several km): the dynamics of populations of relatively mobile species remained correlated over relatively long distances. At the regional level, however, mobility was not a significant factor, implying that widespread environmental stochasticity is of overriding importance at this scale. 6. Although mobility and distance are significant factors in determining population synchrony/asynchrony, the low r 2 values attributable to them indicate that these factors are actually contributing relatively little to the overall dynamics. Butterfly species show local variation in population dynamics, nested within broad scale synchrony which is presumably generated by the climate. Heterogeneity in population dynamics, in local environments, potentially aids metapopulation persistence by buffering the effects of high levels of temporal environmental stochasticity.