Abstract
The potential interactions of grazing, nutrients and light in influencing autotroph species diversity have not previously been considered. Earlier studies have shown that grazing and nutrients interact in determining autotroph species diversity, since grazing decreases species diversity when nutrients (i.e. N or P) limit autotroph growth, but increases it when nutrients are replete. We hypothesized that increased light intensities would intensify the interactions between grazing and nutrients on algal species diversity, resulting in even stronger reductions in algal species diversity through grazing under nutrient–poor conditions, and to even stronger increases of algal species diversity through grazing under nutrient-rich conditions. We studied the effects of grazing (absent, present), nutrients (ambient, N + P enriched) and light (low light, high light) on benthic algal diversity and periphyton C:nutrient ratios (which can indicate algal nutrient limitation) in a factorial laboratory experiment, using the gastropod grazer Viviparus viviparus. Grazing decreased algal biomass and algal diversity, but increased C:P and N:P ratios of periphyton. Grazing also affected periphyton species composition, by decreasing the proportion of Spirogyra sp. and increasing the proportion of species in the Chaetophorales. Grazing effects on diversity as well as on periphyton N:P ratios were weakened when nutrients were added (interaction between grazing and nutrients). Chlorophyll a (Chl a) per area increased with nutrient addition and decreased with high light intensities. Light did not increase the strength of the interaction between grazing and nutrients on periphytic algal diversity. This study shows that nutrient addition substantially reduced the negative effects of grazing on periphytic algal diversity, whereas light did not interact with grazing or nutrient enrichment in determining periphytic algal diversity.
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Acknowledgments
We thank Jockel Liess, Jan Johansson, Elin Tranvik, Lon Willett, Karin Mattsson and the staff of the Erken laboratory for help with the experiment and the analysis of samples. The manuscript was improved by comments from Lon Willett, Lars Tranvik, Tobias Vrede, Alan Steinman and an anonymous reviewer. The project was supported by the Malméns Foundation and by the Oskar and Lili Lamms Minne foundation. A.L. was financed by the Erken Laboratory, and M.K. by the Wallenberg foundation.
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Communicated by Dag Olav Hesse.
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Liess, A., Kahlert, M. Gastropod grazers and nutrients, but not light, interact in determining periphytic algal diversity. Oecologia 152, 101–111 (2007). https://doi.org/10.1007/s00442-006-0636-4
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DOI: https://doi.org/10.1007/s00442-006-0636-4