The spider fauna (Arachnida: Araneae) selected riverside habitats of the Enns and Johnsbach

In Central Europe, hardly any other ecosystem has been altered and destroyed in such a way as the flowing waters and the river basins associated with them: Structural measures in the sense of flood protection and shipping, meliorisation of the valley soils for the extraction of more agricultural land, the construction of power plants for power generation, commercial gravel extraction and many other interventions have dramatically reduced the number of river kilometers still natural or at least close to nature. With this biotope type, all organisms adapted to it threaten to disappear; This would be a catastrophe, as forests, for example, are among the most species-rich habitats in Central Europe. This high biodiversity is due to the dynamics of this habitat coupled with an enormously high productivity: Create at regular intervals (or created) flood catastrophes here and there, thus starting points for a new beginning of plant and animal succession; Thus, there is close coexistence between different ages or mature organism societies. The present work, however, deals primarily with a different, even more extreme and more endangered riverside habitat, the alluvions, i.e. the sediment deposits of a flowing water that are converted in the original state with each flood. These are characterised not only by the aforementioned, high mechanical load, but also by other extreme abiotic factors: Depending on the grain size of the substrate, the (usually very high) sunlight and the distance from the water level, you can find a wide range of site conditions here, from extreme drought and heat to congestion. Few animals and (even fewer plants) have adapted to these inhospitable and often rapidly changing conditions. In particular, weak organisms have specialised in this habitat, many so much that they cannot survive in any other biotope, especially since they are mercilessly displaced by more competitive species.