Colimitation of a freshwater herbivore by sterols and polyunsaturated fatty acids |
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Authors: | Dominik Martin-Creuzburg Erik Sperfeld Alexander Wacker |
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Institution: | 1.Limnological Institute, University of Constance, Mainaustrasse 252, 78464 Konstanz, Germany;2.Institute for Biochemistry and Biology, Theoretical Aquatic Ecology, University of Potsdam, Maulbeerallee 2, 14469 Potsdam, Germany |
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Abstract: | Empirical data providing evidence for a colimitation of an herbivore by two or more essential nutrients are scarce, particularly in regard to biochemical resources. Here, a graphical model is presented, which describes the growth of an herbivore in a system with two potentially limiting resources. To verify this model, life-history experiments were conducted with the herbivore Daphnia magna feeding on the picocyanobacterium Synechococcus elongatus, which was supplemented with increasing amounts of cholesterol either in the presence or the absence of saturating amounts of eicosapentaenoic acid (EPA). For comparison, D. magna was raised on diets containing different proportions of S. elongatus and the cholesterol- and EPA-rich eukaryotic alga Nannochloropsis limnetica. Somatic and population growth of D. magna on a sterol- and EPA-deficient diet was initially constrained by the absence of sterols. With increased sterol availability, a colimitation by EPA became apparent and when the sterol requirements were met, the growth-limiting factor was shifted from a limitation by sterols to a limitation by EPA. These data imply that herbivores are frequently limited by two or more essential nutrients simultaneously. Hence, the concept of colimitation has to be incorporated into models assessing nutrient-limited growth kinetics of herbivores to accurately predict demographic changes and population dynamics. |
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Keywords: | Daphnia magna Synechococcus elongatus Nannochloropsis limnetica multiple resource limitation cholesterol eicosapentaenoic acid |
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