Inducible defenses and community dynamics.
van der Stap, Irene*,1, Vos, Matthijs2, 3, Mooij, Wolf1, 1 Netherlands Institute of Ecology, Nieuwersluis, The Netherlands2 Netherlands Institute of Ecology, Yerseke, The Netherlands3 University of Victoria, Victoria, BC, Canada
ABSTRACT- Theoretical studies have shown that inducible defenses affect food web dynamics and persistence. We performed laboratory experiments to test the theoretical hypotheses. First, we studied the occurrence of colony formation within different algal strains in response to grazing-released infochemicals from the herbivore Brachionus calyciflorus. Then, we observed the effect of inducible defenses on the population dynamics of a freshwater planktonic system using algal strains with different defense strategies and rotifers. Simple food webs were composed of green algae (Scenedesmaceae), herbivorous rotifers (Brachionus calyciflorus and/or Brachionus rubens) and carnivorous rotifers (Asplanchna brightwelli). In this system B. calyciflorus exhibits an inducible defense against predation by developing long spines, while B. rubens does not exhibit a defense in presence of Asplanchna. Our experimental results showed that inducible defenses, as opposed to no defenses, prevent population fluctuations and decrease the strength of trophic cascades. Competition experiments between the two herbivorous rotifers under predation by Asplanchna indicated that inducible defenses may promote coexistence. As a final step, we fitted the theoretical model to the experimental data to understand the mechanisms underlying the observed dynamics.
Key words: Inducible defenses, Food web dynamics, Aquatic ecology
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