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.