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Sökning: db:Swepub > Persson Anders > Tidskriftsartikel > Nilsson Anders > Pettersson Lars

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1.
  • Hansson, Lars-Anders, et al. (författare)
  • Consumption patterns, complexity and enrichment in aquatic food chains
  • 1998
  • Ingår i: Proceedings of the Royal Society, London, B. - Royal Society Publishing. - 1471-2954 (Online) .- 0962-8452 (Print). ; 265:1399, s. 901-906
  • Tidskriftsartikel (refereegranskat)abstract
    • The interactions between consumers and prey, and their impact on biomass distribution among trophic levels, are central issues in both empirical and theoretical ecology. In a long-term experiment, where all organisms, including the top predator, were allowed to respond to environmental conditions by reproduction, we tested predictions from `prey-dependent' and `ratio-dependent' models. Prey-dependent models made correct predictions only in the presence of strong interactors in simple food chains, but failed to predict patterns in more complex situations. Processes such as omnivory, consumer excretion, and unsuitable prey-size windows (invulnerable prey) increased the complexity and created patterns resembling ratio-dependent consumption. However, whereas the prey-dependent patterns were created by the mechanisms predicted by the model, ratio-dependent patterns were not, suggesting that they may be right for the wrong reason'. We show here that despite the enormous complexity of ecosystems, it is possible to identify and disentangle mechanisms responsible for observed patterns in community structure, as well as in biomass development of organisms ranging in size from bacteria to fish.
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2.
  • Persson, Anders, et al. (författare)
  • Effects of enrichment on simple aquatic food webs
  • 2001
  • Ingår i: American Naturalist. - University of Chicago Press. - 0003-0147. ; 157:6, s. 654-669
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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Hansson, Lars-Anders (2)
Brönmark, Christer (2)
Lundberg, Per (2)
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Nyström, Per (2)
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