-1 Research Article Highways and forest fragmentation – effects on carabid beetles (Coleoptera, Carabidae) Matti J. Koivula 1, * and Hendrik J.W. Vermeulen 2 1 Department of Renewable Resources, 4-42 Earth Sciences Building, University of Alberta, Edmonton AB, T6G 2E3, Canada; 2 Secretariaat Stichting WBBS, Kanaaldijk 36, 9409 TV LOON, The Netherlands; *Author for correspondence (e-mail: mkoivula@ualberta.ca) Received 29 April 2004; accepted in revised form 11 May 2005 Key words: Carabidae, Fragmentation, Highway, Isolation, Mark-recapture, Traffic Abstract We conducted two studies on how highways affect their adjacent habitats by sampling carabid beetles (Coleoptera, Carabidae) in patches of formerly continuous forest next to highways. (1) We sampled carabids at 14 highway intersections near Helsinki, Finland. Each intersection (constructed 2–40 years ago) had two forested patches to study: a remnant (0.5–37.4 ha) and, isolated from the remnant by an intersection lane, an islet (size 0.2–1.8 ha). Pitfall trap catch data (2301 carabids, 25 species) showed that remnants hosted higher catches of three carabid species, and slightly higher species richness, than islets (patch-size effect). Time since intersection construction had no apparent effect on carabids. Traffic vol- ume along the intersection lane determined the assemblage structure of carabids in dry patches, and the abundance of a forest carabid Calathus micropterus. Compared to moist patches, drier patches hosted lower catches of four generalist species; they also had different assemblages of carabids (habitat-type effect). An interaction between patch size and habitat type for a forest generalist Pterostichus oblongo- punctatus indicated that the patch-size effect was dependent on habitat type. (2) We examined possible dispersal of carabids among forested patches that were separated by highway lanes in Drenthe, the Netherlands. We released 2696 marked individuals of 10 species, and recaptured 376 using dry pitfall traps. We found no evidence for inter-patch movement for nine forest species, but 22 of 225 recaptured individuals of Poecilus versicolor, an eurytopic open-habitat species, had crossed the highway. Catches of seven forest species were also significantly lower in the road verges, compared to the adjacent forests. These two studies suggest that (i) decreasing patch size negatively affects forest-carabid catch and overall species richness, (ii) habitat type can affect the intensity of the patch-size effect, (iii) carabid assemblages of forest fragments vary with traffic volume (which may be linked with urbanization), (iv) forest carabids rarely cross highways, and (v) open habitats associated with road margins are dispersal barriers for forest carabids. Introduction Roads and their construction affect the biota di- rectly and indirectly (Forman and Alexander 1998; Hourdequin 2000; Trombulak and Frissell 2000). Direct effects of road construction include alter- ation of original habitat, deaths of individuals, and changes in soil chemical properties, water balance and microclimate of habitats (Forman et al. 2003). Moreover, collisions with cars cause additional Landscape Ecology (2005) 20:911–926 Ó Springer 2005 DOI 10.1007/s10980-005-7301-x