Slow, but steady: dispersal of freshwater molluscs |
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Authors: | Heike Kappes Peter Haase |
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Institution: | (1) Department of Limnology and Conservation, Senckenberg Research Institute and Natural History Museum, Clamecystra?e 12, 63571 Gelnhausen, Germany;(2) Biodiversity and Climate Research Centre (LOEWE BiK-F), Senckenberganlage 25, 60325 Frankfurt aM, Germany |
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Abstract: | Molluscs are the proverbial examples of slow movement. In this review, dispersal distances and speed were assessed from literature
data. Active upstream movement can occur both individually and in groups; and depends on traits such as size, sex and reproductive
status, and on external factors such as flow velocity, temperature, sediment structure, and food availability. The potential
for active dispersal follows the sequence Pulmonata ≥ Prosobranchia > Bivalvia, although data for Pulmonata originated from
short-term experiments that likely overestimated dispersal capabilities. Active upstream movement may be 0.3 to 1.0 km per
year for most snails and is probably well below 0.1 km per year for bivalves. Natural passive upstream dispersal increases
the range 10-fold (snails) to 100-fold (bivalves), and anthropogenic vectors can increase upstream dispersal more than 100-fold
(snails) to 1000-fold (bivalves). Three km seems to be the maximal within-stream distance at which many species display regular
population mixing, and at which re-colonisation or successful restoration can be expected within 3–10 years. Lateral dispersal
between unconnected water bodies is passive and mostly known from observational reports, but potential distances depend on
vectors, climate and geomorphology. In general, active dispersal seems insufficient to furnish a compensatory mechanism, e.g.,
for the rate of projected climate change. We provide an overview on dispersal strategies in the light of applied issues. More
rigorous field surveys and an integration of different approaches (such as mark-recapture, genetic) to quantify distances
and probabilities of lateral dispersal are needed to predict species distributions across space and time. |
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