Colonisation credit in recent wet heathland butterfly communities SARA CRISTOFOLI and GRE ´ GORY MAHY University of Liege, Gembloux Agro-Bio Tech, Laboratory of Ecology Passage des de´ porte´ s 2, Gembloux, Belgium Abstract. 1. Wet heathlands and closely associated habitats (e.g. bogs and poor fens) have been highly fragmented over the last two centuries. These habitats nowa- days benefit from large-scale restoration projects, for which the success should be evaluated. 2. Recently, the concept of colonisation credit (the number of species yet to colo- nise a patch) was proposed as a spatially explicit framework to assess recovery in species richness following restoration. In this study, we estimated the colonisation credit of wet heathland butterfly communities in Southern Belgium. The method was applied separately to generalist and specialist species for two reference dates (new patches <25 years old and new patches 25–55 years old). 3. Only a marginally significant colonisation credit was detected for generalist spe- cies. In contrast, we found a significant colonisation credit for specialists, although this was due to a very limited number of strict specialist species. Butterfly community composition differed only marginally between patch age classes. 4. As a general trend, butterfly communities exhibit a rapid response (<25 years) to landscape structure modification. However, conservation and restoration actions should urgently target strict specialists, exhibiting colonisation limitation in new hab- itat patches. A lack of colonisation credit for plant communities in the same land- scape suggests that restoration of wet heathlands may be successful in the short term for various taxonomic groups. Key words. Boloria aquilonaris, butterfly communities, colonisation credit, habi- tat restoration, heathlands. Introduction The continued destruction and fragmentation of natural and semi-natural habitats have been identified as the main causes of biodiversity decline (Olivieri & Vitalis, 2001). Protection and management of the remaining (semi-) natural habitat fragments is no longer sufficient to ensure the long-term viability of all ele- ments contributing to biodiversity (Bennett, 1997). Conse- quently, habitat restoration has become a necessity to recreate functional ecological networks. However, ecological restoration is often costly or even cost-prohibitive. Successful funding of habitat restoration will be more likely when a high probability of success can be provided. Recently, Cristofoli et al. (in press) proposed a methodology that aims to quantitatively evaluate the colonisation success of newly created habitat patches in an expli- cit spatial context. The approach is rooted in the extinction debt hypothesis (Hanski, 1994; Tilman et al., 1994). Some species, because of their intrinsic characteristics, exhibit a time lag when responding to landscape change. In the context of ecological res- toration, the phase of recovery of biotic and abiotic conditions meeting the species requirements may also contribute to a time lag in the species response to landscape change. Subsequently, non-equilibrium between species richness and the spatial charac- teristics of the habitat is possible in newly created or restored habitat patches. Namely, new habitat patches may experience a colonisation credit and demonstrate lower species richness com- pared to theoretical expectations based on the spatial properties of the patch. A colonisation credit is defined as the number of species yet to colonise a patch following landscape changes, until an equilibrium is reached between species richness and patch spatial properties (Cristofoli et al., in press). On one hand, wet heathlands and closely associated habitats (i.e. bogs and poor fens) have been highly fragmented over the Correspondence: Sara Cristofoli, University of Liege, Gemb- loux Agro-Bio Tech, Laboratory of Ecology Passage des de´porte´s 2, 5030 Gembloux, Belgium. E-mail: cristofoli.s@fsagx.ac.be Insect Conservation and Diversity (2010) 3, 83–91 doi: 10.1111/j.1752-4598.2009.00075.x Ó 2009 The Authors Journal compilation Ó 2009 The Royal Entomological Society 83