This Ph.D.-thesis aimed to address which environmental factors influence the assemblage structure of mobile, riparian arthropods along spatially structured river banks of a rain-fed, lowland gravel river, the Common Meuse. As riverine ecosystems are basically non-equilibrium, dynamic ecosystems, mainly flow regimes and flood pulse characteristics are expected to shape both the distribution and behaviour of its inhabitants. The river banks along the Common Meuse are (in)frequently disturbed by flood events and liable to extreme microclimatological conditions. Hence, functional life-history traits of the present species, particularly spiders (Araneae) and carabid beetles (Carabidae), supposedly affect species composition as well. Moreover, organisms occurring within a highly structured system and which are repeatedly exposed to flooding disturbance, are expected to have evolved or adjusted their behavioural responses in accordance with their functional life-history characteristics such as habitat affinity and mobility. Correspondingly, less mobile species are expected to show variation in their spatial genetic structure as well.
Based on an intensive pitfall survey, increased anthropogenic alterations of water discharges were shown to cause the loss of stenotopic, xerothermophilic and less mobile riparian arthropods. Next to it, the results of two field experiments indicated that movement decisions of two sympatric wolf spiders (Lycosidae) were guided, particularly, by factors related to their population of origin (side of the river; either genetics or experience). A stenotopic riparian wolf spider, however, relied more on individual information (e.g. visual signals) and showed a higher degree of behavioural plasticity. This might increase the beneficiality of flood-avoiding behaviour. By using Amplified Fragment Length Polymorphism (AFLP) markers, the genetic population structure of the highly stenotopic wolf spider Pardosa agricola (Thorell, 1856) was studied. Nearby populations were less differentiated genetically than populations on different sides of the river, indicating the importance of functional connectivity along the riparian corridor.
River restoration and the rehabilitation of the riparian corridor should generate the required heterogeneity at the river bank level, hence increasing the sustainability of dynamic lowland river systems and realizing the conservation of vulnerable riparian arthropods. River management should consider the management of the alluvial hinterland as well to provide suitable refuges during flooding
