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Evolution of Dispersal Ability in the Speckled Wood Butterfly
Hughes, C.L., Dytham, C. and Hill, J.K. 2007. Modelling and analyzing evolution of dispersal in populations at expanding range boundaries. Ecological Entomology 32: 437-445.

What was done
Evolutionary changes in adult flight morphology were examined in six populations of the speckled wood butterfly -- Pararge aegeria L. (Satyrinae) -- along a transect from its distribution core to its warming-induced northward expanding range margin in Britain. The results of this exercise were then compared with the output of an individual-based spatially explicit model that was developed "to investigate impacts of habitat availability on the evolution of dispersal in expanding populations."

What was learned
The authors report that the empirical data they gathered "were in agreement with model output," and that they "showed increased dispersal ability with increasing distance from the distribution core," which included favorable changes in thorax shape, abdomen mass and wing aspect ratio for both males and females, as well as thorax mass and wing loading for females. In addition, they say that "increased dispersal ability was evident in populations from areas colonized >30 years previously."

What it means
Hughes et al. suggest that "evolutionary increases in dispersal ability in expanding populations may help species track future climate changes and counteract impacts of habitat fragmentation by promoting colonization." However, they say that in the specific situation they investigated, "at the highest levels of habitat loss, increased dispersal was less evident during expansion and reduced dispersal was observed at equilibrium, indicating that for many species, continued habitat fragmentation is likely to outweigh any benefits from dispersal." Put another way, it would appear that global warming is proving not to be an insurmountable problem for the speckled wood butterfly, which is evolving physical characteristics that allow it to better keep up with the poleward migration of its current environmental niche, but that the direct destructive assaults of humanity upon its natural habitat could well end up driving it to extinction.

Reviewed 9 April 2008