Species assembly in ground beetle (Coleoptera: Carabidae) communities in local microhabitats was studied in a forest. The following questions were addressed: are there important filters that sort the species in the assemblages? If so, what is the specific nature of these filters? In order to address these questions rarefaction analysis was used to determine whether ground beetle species are distributed non-randomly. Next, the nature of filters was determined by analyzing (1) the community matrix and searching for the consequences of competitive exclusion and (2) species-environmental relations. Rarefaction analysis revealed that the species composition is filtered: species richness was less than expected and there were fewer than expected congeneric species coexisting at high beetle population densities. However, community matrix and body size analyses did not detect significant competition among the beetle species and the matrix was significantly nested. Species-environmental analyses indicated that the ground beetle assembly was strongly linked to ground vegetation. It is concluded that spatial distribution of ground beetles across local communities in this forest habitat is determined more by local environmental conditions than competition, and ground beetles do not interact strongly among themselves so that competitive effects do not play an important role in their distribution except at high beetle population densities. and Sonomi Shibuya, Kohei Kubota, Masahiko Ohsawa, Zaal Kikvidze.
Little is known about changes in the significance of environmental filtering and neutral processes during the succession of plant communities. Generally, a succession is expected to be trait-driven and a shift is predicted from high importance of seed dispersal ability in initial phases to importance of strong competitive ability in later stages. In this study, we consider a community assembly trait-driven in the case of a shift in functional traits during succession and randomly assembled in the case there is no shift in functional traits during succession. We therefore tested whether urban plant communities show trait convergence or trait divergence in relation of successional stage, water and nutrient availability. At two scales (100 × 100 cm and 10 × 10 cm), we analysed traits relevant to seed dispersal, stress tolerance and competitive ability and compared real data with null models. We subsequently used regression trees to associate convergence and divergence to plot age and stress due to low water and soil nutrient availability. Most traits were neither significantly convergent nor divergent and the variance explained by the regression trees was often lower than 20 %. We found divergence in seed number instead of the expected convergence towards high seed number. In accord with expectations we found low seed terminal velocity and annual life span in early succession. Convergence in seed bank longevity occurred at intermediate plot age, and convergence in the combination of life span and lateral spread showed the relevance of competition filtering in the most fertile plots. On the other hand, competition-induced convergence in canopy height or specific leaf area was not supported by our results. We concluded that, based on the traits considered in this study, the overwhelming evidence was that community assembly during the first 40 years of succession was driven by trait-neutral mechanisms.