Dispersal distance and the pool of taxa, but not barriers, determine the colonisation of restored river reaches by benthic invertebrates

Abstract

1. Restoration is an increasingly central theme in river ecology. Recent studies have highlighted the importance of the species pool in the surrounding river network for determining colonisation of restored river reaches by both invertebrates and fish. 2. Using a comprehensive data set of 21 river restoration sites and 292 sites in the immediate surroundings, we tested the influence of distance to nearest colonist source on invertebrate colonisation based on a comparison of river network distances and Euclidean distances, expecting river network distances would better align with colonisation rates. We then assessed the importance of dispersal distance in relation to several other parameters, such as the number and intensity of barriers along the river network, surrounding taxon pool occupancy rate, physical characteristics of the restored sites and restoration techniques used in determining colonisation of commonly occurring benthic invertebrates. 3. We hypothesised that (i) distance would be critical, with colonisation of restored sites declining with increasing distance; (ii) barriers between these sites would be a minor, but taxon-specific, influence on the colonisation; and (iii) the higher the regional pool occupancy rate of a certain taxon, the higher its probability of presence at a restored site. 4. Overall, taxon pool occupancy rate was the most important driver of colonisation likelihood, followed by distance to nearest source, with the first kilometre particularly important. The effect of barriers was minor but significant, and taxon identity had no effect on the predictive ability of the model. Factors associated with the restoration projects such as techniques used and physical characteristics had minor influences, being completely outweighed by taxon pool and dispersalrelated factors. 5. To gauge the likelihood of successful outcomes of habitat restoration projects, we suggest it is important to assess regional taxon pools and ensure distances between healthy populations are minimised. These results clearly emphasise the importance of spatial planning for restoration projects.

The role of benthic microhabitats in determining the effects of hydromorphological river restoration on macroinvertebrates

“…4 Relationships between the differences in microhabitat diversity and patchiness between the restored and the degraded river sections, expressed as the Osenberg response ratio (Dr) of the microhabitat diversity (Shannon-Wiener Index; SWI) and de microhabitat patchiness (Spatial Diversity Index; SDI), and its associated differences in macroinvertebrate metrics, the modified Osenberg response ratio (Dr m ) for: A total richness, B EPT diversity, C EPT richness, and D Microhabitat preference types diversity. Values [ 0 denote a positive effect, and negative values denote a negative effect restored river section and a potential source population is large and the targeted species have a low dispersal ability (Tonkin et al, 2014). In our study, the mean project age for the rivers studied was ten years, which might be sufficient for more strongly dispersing taxa to reach the restored site (Fuchs & Statzner, 1990), but perhaps not for weaker dispersers (e.g.…”

Agricultural Rivers at Risk: Dredging Results in a Loss of Macroinvertebrates. Preliminary Observations from the Narew Catchment, Poland

“…It is likely that small agricultural rivers that are "maintained" by regular dredging, contra the examples given by Chester and Robson [1] and supported with the observations of Tonkin et al [20], will never again serve as a refuge for freshwater biodiversity. Avoiding this scenario will require management approaches, especially in cases of small agricultural rivers, to be individualized so each of the complex river ecosystems could retain its unique and specific environmental values [25].…”

“…It is likely that in the long run the self-restoration of the dredged river stretches analyzed may result in the re-establishment of hydromorphological conditions by allowing the re-development of macroinvertebrate abundance and species composition toward the reference values reported for non-dredged stretches [19,20]. However, if long headwater parts of these rivers remain under the pressure of dredging every 1-3 years (which is the case of analyzed and adjacent rivers), it is likely that the spontaneous restoration of macroinvertebrate populations of the whole river systems may be-if still possible-very slow.…”

Scaling fish metacommunities in stream networks: synthesis and future research avenues

“…These restoration activities often fail, because they do not consider the importance of dispersal relationships in the landscape and/or because they wrongly address the protection of communities which are by far suboptimal for conservation (Bond and Lake 2003, Palmer et al 2010, Tonkin et al 2014, Schmutz et al 2016. The key message of applied metacommunity research is a spatially more explicit, landscape scale consideration of between community relationships for the success of restoration and conservation.…”