Food web structure and planktonic predator-prey relationships in two eutrophic European lakes: Stability constraints on carbon fluxes

Laws, Edward A.

Limnol. Oceanogr., 53(2), 2008, 760-772 | DOI: 10.4319/lo.2008.53.2.0760

ABSTRACT: The food webs in two eutrophic European lakes were analyzed with respect to their stability characteristics. The food web during the summer in Lake Nesjøvatn (Norway) appeared to be stable; its response time to small perturbations was ~12 d. In Lake Kastoria (Greece), the summer food web was almost neutrally stable, with a response time of ~160 d. The major difference in the two systems was the species composition of the phytoplankton community, which was dominated by unicellular cryptophytes in Lake Nesjøvatn and by toxic filamentous and colonial cyanobacteria in Lake Kastoria. The macrozooplankton in both lakes showed a distinct inclination toward carnivory versus herbivory, and the heterotrophic flagellates showed a preference for small phytoplankton versus heterotrophic bacteria as a food source. The requirement for stability of the food webs constrains the grazing rates of predators to values substantially less than those that would maximize the energy flux through the system. This is especially true when a predator preferentially consumes one of several prey species.

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