Abundance changes in orb-weaver spider communities at the edge of the Argiope bruennichi expansion range.

Expanding range is an inherent feature of any species and may be caused by climate change, destruction or other change of habitat, or lack of natural enemies. In a new habitat the species may be neutral, or as predator it can displace related species through competition. A strong expansion to northern Europe was observed in the thermophilous spider species Argiope bruennichi. The species doubled its range in Poland during the 1990s and its impact on native species was not investigated so far. In this article, the results of studies about A. bruennichi number (density) and its contribution in orb-weaver spider communities are analysed. We also try to determine the impact of newly occurring species on the local araneofauna.

Spatial Niche Separation on the Periphery Range of Argiope bruennichi and Its Effect With Araneus quadratus (Araneae: Araneidae).

Recent decades have witnessed an intensified expansion of thermophilic organisms from southern into northern Europe. Argiope bruennichi, an orb-weaver spider species, is extending its range relatively fast and gradually becoming a common species in Europe. The aim of this study was to investigate how this relatively newly-come taxon is affecting another orb-weaver spider species and whether it demonstrates features of an invasive species. Interactions were examined between this species and another dominant species with similar body and web size, Araneus quadratus. The study areas were located in two adjacent regions in northeast Poland: the warmer Mazury Lake District and the colder Suwalki Lake District. The areas differed in both population density of the studied species as well as in climatic conditions. Six study sites were selected in each region. In the Mazury Lake District, A. bruennichi was more frequent than A. quadratus; this relationship was reversed in the Suwalki Lake District. We measured the height of the web hub above the ground and the height of the plants to which webs were fixed. Web location height was chosen as an indicator of the interaction. The results indicate that A. quadratus located its webs higher than A. bruennichi, regardless of species abundance and region. A. bruennichi does not exert a significant negative impact on A. quadratus web placement. The two species clearly prefer different heights, which in turn may determine the kind of prey they catch.