Transient Dynamics of Pelagic Producer-grazer Systems in a Gradient of Nutrients and Mixing Depths

Phytoplankton—grazer dynamics are often characterized by long transients relative to the length of the growing season. Using a phytoplankton—grazer model parameterized for Daphnia pulex with either flexible or fixed algal carbon: nutrient stoichiometry, we explored how nutrient and light supply (the...

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Bibliographic Details
Published in:	Ecology (Durham) Vol. 89; no. 5; pp. 1272 - 1286
Main Authors:	Jäger, C.G, Diehl, S, Matauschek, C, Klausmeier, C.A, Stibor, H
Format:	Journal Article
Language:	English
Published:	Washington, DC Ecological Society of America 01-05-2008
Subjects:	Algae algae–grazer interaction Animal and plant ecology Animal populations Animal, plant and microbial ecology Animals Biological and medical sciences Biomass Biomass production C:P ratio carbon Computer Simulation Crustaceans Daphnia Daphnia - physiology Daphnia pulex Ecological modeling ecological stoichiometry Ecology Ecosystem ecosystems Eukaryota - physiology Feeding Behavior - physiology Fertilizers field experimentation Food food quality Fresh Water Freshwater Fundamental and applied biological sciences. Psychology General aspects grazing growing season light light enrichment Limnology Mixing height Modeling Models, Biological nutrient enrichment Nutrients Oceans and Seas paradox of energy enrichment phosphorus Phytoplankton Phytoplankton - physiology Plankton population density Population Dynamics population model population oscillations seasonal succession simulation models Stoichiometry trophic relationships Stoichiometry food quality Cladocera algae-grazer interaction Depth Crustacea population oscillations Medium enrichment Dynamics Seasonal variation Light Quality Oscillation Daphnia Ratio Branchiopoda nutrient enrichment Algae Interaction seasonal succession Ecology C:P ratio light enrichment Pelagic zone Feeding ecological stoichiometry Arthropoda paradox of energy enrichment Nutrient population model Models Invertebrata
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Summary:	Phytoplankton—grazer dynamics are often characterized by long transients relative to the length of the growing season. Using a phytoplankton—grazer model parameterized for Daphnia pulex with either flexible or fixed algal carbon: nutrient stoichiometry, we explored how nutrient and light supply (the latter by varying depth of the mixed water column) affect the transient dynamics of the system starting from low densities. The system goes through an initial oscillation across nearly the entire light—nutrient supply space. With flexible (but not with fixed) algal stoichiometry, duration of the initial algal peak, timing and duration of the subsequent grazer peak, and timing of the algal minimum are consistently accelerated by nutrient enrichment but decelerated by light enrichment (decreasing mixing depth) over the range of intermediate to shallow mixing depths. These contrasting effects of nutrient vs. light enrichment are consequences of their opposing influences on food quality (algal nutrient content): algal productivity and food quality are positively related along a nutrient gradient but inversely related along a light gradient. Light enrichment therefore slows down grazer growth relative to algal growth, decelerating oscillatory dynamics; nutrient enrichment has opposite effects. We manipulated nutrient supply and mixing depth in a field enclosure experiment. The experimental results were qualitatively much more consistent with the flexible than with the fixed stoichiometry model. Nutrient enrichment increased Daphnia peak biomass, decreased algal minimum biomass, decreased the seston C:P ratio, and accelerated transient oscillatory dynamics. Light enrichment (decreasing mixing depth) produced the opposite patterns, except that Daphnia peak biomass increased monotonously with light enrichment, too. Thus, while the model predicts the possibility of the "paradox of energy enrichment" (a decrease in grazer biomass with light enrichment) at high light and low nutrient supply, this phenomenon did not occur in our experiment.
Bibliography:	Corresponding Editor: R. W. Sterner. ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0012-9658 1939-9170
DOI:	10.1890/07-0347.1