Authors: A Liess K Lange
Publish Date: 2011/03/25
Volume: 167, Issue: 1, Pages: 85-96
Abstract
Ecological stoichiometry has advanced food web ecology by emphasising the importance of food quality over food quantity for herbivores Here we focus on the effects of abiotic factors such as nutrients and light known to influence food quality on grazer growth rates As model organism we used the mudsnail Potamopyrgus antipodarum that is native to New Zealand but invasive elsewhere In a stream channel experiment in New Zealand we manipulated light two levels and nutrients four levels to achieve a range of primary producer carbon nutrient ratios and added mudsnails 3 densities + ungrazed control to 128 periphyton covered stream channels in a 2 × 4 × 4 full factorial design We measured snail growth rate and activity food quality and nutritional imbalance to test the predictions that 1 less light and more nutrients increase periphyton food quality and thus snail growth rates and 2 less crowding leads to higher food availability and thus higher snail growth rates We found that snail growth rates were higher under low light than under high light intensities and this difference increased with increasing nutrient addition These changes in growth rate were not mediated by food quality in terms of periphyton nutrient ratios Furthermore experimental treatments strongly affected snail behaviour Snails grazed more actively in the low light treatments and thus it is more likely that snail growth rates were directly affected by light levels maybe as a result of innate predator avoidance behaviour or as a reaction to high UV intensities We conclude that in our stream channels snail growth rate was limited by factors other than food quality and quantity such as UV exposure algal defences or the relatively low ambient water temperatureWe thank Christoph Matthäi Jay Piggott Friederike Schulz Mathilde Berahou Fabien Champion Sarai Cosgrove Barry Baxter Peter Herrmann Nicky McHugh and Julie Clark for help in the field and in the laboratory Colin Townsend provided helpful advice We thank C Douglas for the use of his land and the Department of Conservation for permits to work in the Kauru River The manuscript was improved by comments from Mary Power Carolyn Faithfull Birte Reichstein Kathrin Lengfeller Owen Rowe Robert Hall and two anonymous reviewers AL was financed by a postdoctoral scholarship of the Swedish Research Council for Environment Agriculture and Spatial Planning FORMAS
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