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Effects of enrichment on simple aquatic food webs

Author:
  • Anders Persson
  • Lars-Anders Hansson
  • Christer Brönmark
  • Per Lundberg
  • Lars Pettersson
  • L Greenberg
  • Anders Nilsson
  • Per Nyström
  • Pia Romare
  • L Tranvik
Publishing year: 2001
Language: English
Pages: 654-669
Publication/Series: American Naturalist
Volume: 157
Issue: 6
Document type: Journal article
Publisher: University of Chicago Press

Abstract english

Simple models, based on Lotka-Volterra types of interactions between predator and prey, predict that enrichment will have a destabilizing effect on populations and that equilibrium population densities will change at the top trophic level and every second level below. We experimentally tested these predictions in three aquatic food web configurations subjected to either high or low nutrient additions. The results were structured by viewing the systems as either food chains or webs and showed that trophic level biomass increased with enrichment, which contradicts food chain theory. However, within each trophic level, food web configuration affected the extent to which different functional groups responded to enrichment. By dividing trophic levels into functional groups, based on vulnerability to consumption, we were able to identify significant effects that were obscured when systems were viewed as food chains. The results support the prediction that invulnerable prey may stabilize trophic-level dynamics by replacing other, more vulnerable prey. Furthermore, the vulnerable prey, such as Daphnia and edible algae, responded as predicted by the paradox of enrichment hypothesis; that is, variability in population density increased with enrichment. Hence, by describing ecosystems as a matrix of food web interactions, and by recognizing the interplay between interspecific competition and predation, a more complete description of the ecosystem function was obtained compared to when species were placed into distinct trophic levels.

Keywords

  • Ecology
  • predation
  • paradox of enrichment.
  • variability
  • stability
  • food chain

Other

Published
  • ISSN: 0003-0147
Lars B. Pettersson
E-mail: lars [dot] pettersson [at] biol [dot] lu [dot] se

Researcher

Biodiversity

+46 46 222 38 18

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Centre for Animal Movement Research
Evolutionary Ecology, Department of Biology
Ecology building S-223 62 Lund Sweden