Poleward shifts in geographical ranges of butterfly species associated with regional warming

Mean global temperatures have risen this century, and further warming is pr edicted to continue for the next 50-100 years(1-3) Some migratory species c an respond rapidly to yearly climate variation by altering the timing or de stination of migration(4), but most wildlife is sedentary and so is incapab le of such a rapid response. For these species, responses to the warming tr end should be slower, reflected in poleward shifts of the range. Such chang es in distribution would occur at the level of the population, stemming not from changes in the pattern of individuals' movements, but from changes in the ratios of extinctions to colonizations at the northern and southern bo undaries of the range. A northward range shift therefore occurs when there is net extinction at the southern boundary or net colonization at the north ern boundary. However, previous evidence has been limited to a single speci es' or to only a portion of the species' range(6,7). Here we provide the fi rst large-scale evidence of poleward shifts in entire species' ranges. In a sample of 35 non-migratory European butterflies, 63% have ranges that have shifted to the north by 35-240 km during this century, and only 3% have sh ifted to the south.