Eero Halme

Small-scale heterogeneity in the spatial distribution of carabid beetles in the southern Finnish taiga

Small-scale distribution of ground beetles (Cole- optera, Carabidae) was examined, based on catches among 300 pitfall traps, in a coniferous forest in southern Finland. The sample from the whole snow-free season comprised 2405 individuals of twenty-two species. Each of the most numerous species (Pterostichus oblongopunctatus (F.), Calathus micropterus (Dft.), Leistus terminatus (Hellw. in Pz.), Notiophilus biguttatus (F.) and Cychrus caraboides (L.)) was non-randomly distributed and formed aggrega- tions within the site of c. 1.3 ha in area. Although the five species occurred in every microhabitat defined in the plot, four of them (N. biguttatus was an exception) were more abundantly found in certain microhabitat types than in the others. In addition to vegetation around the traps, the numbers of Formica ants in the traps correlated with the numbers of carabids caught, mostly negatively. The consid- erable variation in catches and species richness among single traps and among blocks of 16 traps tended to even out, when larger subsamples were taken from the total pool (blocks of 48 traps). The distribution patterns observed within the plot were compared to a reference data set from similar habitat in the same region. Species distributions among microhabitats were slightly different in the reference set and the predic- tive success was relatively poor, probably due to different scales of study in the two data sets. Variation in species distribution in the two spatial scales studied (within a habitat patch and among them) is suppos- edly due to different factors. Although no direct evidence is available from our study area, we suggest that active micro- habitat selection explains the small-scale distribution within the study plot, whereas dynamics of local populations, influenced by regional-scale differences in habitat composi- tion, are the most likely explanation for the distribution pat- terns among habitat patches.

Effects of Forest Fragmentation on Carabid Assemblages in the Urban Setting: Implications for Planning and Management

We compared carabid beetle assemblages (Coleoptera, Carabidae) between large (9.6–21.5 ha), medium-sized (4.2–8.2 ha), small forest fragments (0.5–3.0ha), their surrounding agro-urban habitats and a nearby continuous forest in southern Finland. Carabid species richness was lowest in the continuous forest and highest in the surroundings. In a multivariate analysis of vegetation and carabid samples, sites from each fragment size class formed groups of their own and the small fragments were found to be similar to the surroundings. The proportion of open-habitat species increased with decreasing fragment size indicating that open habitat species easily invade the small fragments from the surroundings. Some specialised forest carabids were exclusively caught in the continuous forest. To preserve forest arthropod faunas in urban areas it is essential to leave large, continuous forest tracts untouched. Since this may be difficult to achieve, sizeable forest fragments must be set aside and ecological networks of forested habitats must be created.