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The worldwide transport of species beyond their native range is an increasing problem, e.g. for global biodiversity. Many introduced species are able to establish in new environments and some even become invasive. However, we do not know which traits enable them to survive and reproduce in new environments. This study aims to identify the characteristics of exotic ants, and to quantitatively test previously postulated but insufficiently tested assumptions. We collected data on nine traits of 93 exotic ant species (42 of them being invasive) and 323 native ant species in North America. The dataset includes 2536 entries from over 300 different sources; data on worker head width were mostly measured ourselves. We analyzed the data with three complementary analyses: univariate and multivariate analyses of the raw data, and multivariate analyses of phylogenetically independent contrasts. These analyses revealed significant differences between the traits of native and exotic ant species. In the multivariate analyses, only one trait was consistently included in the best models, estimated with AICc values: colony size. Thus, of the nine investigated traits, the most important characteristic of exotic ants as compared to native ants appears to be their large colony size. Other traits are also important, however, indicating that native and exotic ants differ by a suite of traits.
Compared to other grassland types across Slovakia, dry grasslands harbour species-rich and specialised ant communities. High diversity and species richness of ants may be seen as a consequence of (i) the specific structure of dry grassland vegetation, (ii) long-term ecological stability, and (iii) currently low or absent management-induced disturbance. With special regard to dry grasslands, we report on structural characteristics of vegetation and low-disturbance regime, which contribute to ant assemblage structure. Our study was carried out in the Štiavnické Vrchy Mts. (Central Slovakia), a region with a historically well-developed grassland area. We established a set of 25 research plots within southorientated grassland habitats representing five different grassland types: wet managed and wet abandoned grasslands, mesic managed and mesic abandoned grasslands (Arrhenatherion elatioris), and dry abandoned grassland habitats (Asplenio-Festucion glaucae). Each habitat type was represented by five plots. At each plot, a set of ten pitfall traps was used to sample ground-foraging ant assemblages. Around each trap, structural characteristics of vegetation and microhabitat were assessed. Dry grasslands were shown to have a specific microhabitat structure, characterised by the presence of a well-developed moss and lichen layer, exposed bedrock, bare soil, and significantly lower, although species-rich vege - tation. Besides the specific microhabitat structure, the absence of management may have contributed to the distinctiveness of these ant assemblages compared to those associated with other grassland categories. Ant assemblages were more species-rich, and the activity of ants was higher in recently abandoned grassland habitats. The effect of abandonment was quite opposite for plants, whose species-richness was, contrary to ants, higher within managed sites.