Dispersal in pond snails: potential role of waterfowl

Abstract

Young pond snails of three species (Lymnaea stagnalis, Stagnicola elodes, and Helisoma trivolvis) were allowed free access to waterfowl feathers floating on the surface of shallow containers. Snails adhering to the feathers were subjected to simulated flight conditions by placing them in an air stream. The size of these snails, the length of time they adhered to the feathers while in the air stream, and their survivability for various lengths of time under these conditions were recorded. Those snails that adhered to the feathers were mainly small individuals (< 2.5 mm long in all three species). The proportion that remained clinging to the feathers declined sharply with time; after 15 min of exposure only 6% of L. stagnalis, 18% of S. elodes, and 15% of H. trivolvis remained. Survivability also declined with time exposed to the simulated flight conditions; after 15 min only 50% of L. stagnalis, 23% of S. elodes, and 15% of H. trivolvis were still alive. Larger individuals tended to survive better than smaller ones for any given exposure time, but they also tended to fall off the feathers sooner than smaller ones; no snail more than 3 mm long was recorded adhering to the feathers for more than 4 min under the test conditions of simulated flight (air speed of 41 km/h). These results suggest that despite a low proportion of the snail population adhering to the feathers (< 1% of those available at any given time) and the relatively high rates of loss, either by falling off the feathers or dying in situ after adhering, the probability of successful dispersal for distances up to 10 km remains high (a mallard flying for 15 min at 41 km/h was deemed capable of carrying at least three surviving individuals of any of the species tested over a distance of about 10 km). Of the three species tested, S. elodes had the greatest probability of successful dispersal, which may explain its almost ubiquitous distribution in the water bodies of central Alberta.