Impacts of landscape structure on butterfly range expansion

Since the 1940s, the distributions of several butterfly species have been e xpanding in northern Europe, probably in response to climate warming. We fo cus on the speckled wood butterfly Pararge aegeria in order to determine im pacts of habitat availability on expansion rates. We analyse observed expan sion rates since 1940 and also use a spatially explicit mechanistic model ( MIGRATE) to simulate range expansion in two areas of the UK which differ in their distribution of breeding habitat (woodland). Observed and simulated expansion rates were in very close agreement but were 42%-45% slower in an area that had 24% less woodland. Unlike P. aegeria, the majority of butterf ly species are not currently expanding, almost certainly because of lack of suitable habitat. Incorporating the spatial distribution of habitat into i nvestigations of range changes is likely to be important in determining tho se species that can and cannot expand, and for predicting potential future range changes.