Effects of habitat fragmentation on carabids in forest patches

Aim The aim of this study was to test some of the classical rules of island biogeography for the carabid beetles (Coleoptera: Carabidae) in 15 forest patches during 1995-99. Location The 15 forest patches studied are located on the Bereg Plain. The Bereg Plain is at the foot of the Carpathians, partly in Hungary and partly in the Ukraine. Even in recent times, the area was covered by continuous woodland of deciduous trees, and the species of the closed canopy deciduous forest of the hills and mountains were able to disperse from the Carpathians to these lowland forests. But now, because of agricultural activities and forest management, this woodland is fragmented into forest patches. Methods The species-area and the number of species-distance to mainland relationships, and the influence of other factors like shape, isolation, and altitude above the see level, on the number of species were studied. We have used three categories of species during the analyses: (i) total number of species; (ii) the number of species of the closed canopy deciduous forest of the hills and mountains (ForHim species); and (iii) the number of widely distributed generalist species (WidGe species). Results There were positive, but statistically insignificant correlations between the distance to the Carpathians and the total number of species, and also between the distance to the Carpathians and the number of WidGe species. The correlation was negative for the number of ForHim species, and it was also not significant. There were significant negative correlation between both the total number of species and the number of WidGe species and the size of the forest patches, while there were significant positive correlation between the size of forest patch and the number of ForHim species. The number of ForHim species decreased significantly by the increase of isolation, while the number of WidGe species increased by the isolation. Shape of the forest patches, and their altitude above the sea level had no influence on the total species richness, the ForHim species richness, and the WidGe species richness. We have also proved that each of the total species richness, the ForHim species richness, and the WidGe species richness, is higher for many small forest patches than for one large patch of the same total area. Main conclusions Our results suggest that historical reasons have a vital influence on the present species patterns. Moreover, in biogeographical studies we must distinguish between species which recognize the habitat as a patch or island and those that can survive in the neighbouring habitats as well. An ignorance of these two categories may disguise basic biogeographic rules.