Omnivory by Planktivores Stabilizes Plankton Dynamics, but May Either Promote or Reduce Algal Biomass |
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Authors: | José Luiz Attayde Egbert H van Nes Aderaldo I L Araujo Gilberto Corso Marten Scheffer |
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Institution: | 1. Centro de Biociências, Universidade Federal do Rio Grande do Norte, Natal, RN, Brazil 2. Department of Aquatic Ecology and Water Quality Management, Wageningen University, Wageningen, The Netherlands 3. Departamento de Física Teórica e Experimental, UFRN, Natal, RN, Brazil 4. Instituto Federal de Ensino, Ciência e Tecnologia do Ceará, Fortaleza, CE, Brazil
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Abstract: | Classical models of phytoplankton–zooplankton interaction show that with nutrient enrichment such systems may abruptly shift
from limit cycles to stable phytoplankton domination due to zooplankton predation by planktivorous fish. Such models assume
that planktivorous fish eat only zooplankton, but there are various species of filter-feeding fish that may also feed on phytoplankton.
Here, we extend these classical models to systematically explore the effects of omnivory by planktivorous fish. Our analysis
indicates that if fish forage on phytoplankton in addition to zooplankton, the alternative attractors predicted by the classical
models disappear for all realistic parameter settings, even if omnivorous fish have a strong preference for zooplankton. Our
model also shows that the level of fish biomass above which zooplankton collapse should be higher when fish are omnivorous
than when fish are zooplanktivorous. We also used the model to explore the potential effects of the now increasingly common
practice of stocking lakes with filter-feeding fish to control cyanobacteria. Because omnivorous filter-feeding fish forage
on phytoplankton as well as on the main grazers of phytoplankton, the net effect of such fish on the phytoplankton biomass
is not obvious. Our model suggests that there may be a unimodal relationship between the biomass of omnivorous filter-feeding
fish and the biomass of phytoplankton. This implies that to manage for reductions in phytoplankton biomass, heavy stocking
or strong reduction of such fish is best. |
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