Biotic and abiotic drivers of macroinvertebrate dispersal
Dispersal of lotic organisms is a fundamental control of riverine biodiversity, yet the drivers and dynamics of dispersal processes still remain poorly understood, which renders predictions of invertebrate dispersal highly uncertain. Knowledge gaps exist as to the population’s proportion of members that actually disperse, the members’ individual dispersal capabilities and the role of spatial habitat heterogeneity (niche availability). Accordingly, dispersal predictions for lotic macroinvertebrates continue to rely on indirect proxies (i.e. dispersal traits), rather than on direct measurements of realised dispersal distances. Further, biotic interactions at the population (e.g. density) and community levels (competition, predation, parasitism) are likely to initiate (or inhibit) dispersal, but are rarely considered in dispersal studies.
A comprehensive field dispersal experiment will be performed for selected hololimnic and merolimnic as well as dispersive and philopatric species in both model catchments (Emscher/Boye, Kinzig). The population sizes will be estimated by benthic samples (hand nets) of all relevant microhabitats and emergence traps at eight sampling sites each per catchment. The distances crossed by individual members of a population will be quantified by an array of instream (drift nets) and terrestrial dispersal traps (Malaise and sticky traps) at four sites each per catchment. Isotope enrichment (15NH4Cl) upstream of dispersal sites will be used to label large quantities of the model species’ populations. Dispersal traps will be located at predefined distances up- and downstream (dispersal along the stream corridor) as well as perpendicular to the stream course (overland dispersal).
Environmental and spatial variables at various spatial scales (e.g. land cover, riparian conditions, hydrology, physical habitat, physico-chemistry) will complement the biological data, to determine niche availability and ultimately, to test spatial versus environmental and biological versus abiotic descriptors of realised dispersal. Comparing the urban Emscher/Boye catchment with the rural Kinzig catchment will allow to address catchment-related characteristics and stressor history, i.e. legacy effects on dispersal patterns.