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Ontogenetic Diet Shifts Result in Niche Partitioning between Two Consumer Species Irrespective of Competitive Abilities
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Aquatic Ecology)
Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, the Netherlands. (Theoretical Ecology)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Aquatic Ecology)
2010 (English)In: American Naturalist, ISSN 0003-0147, E-ISSN 1537-5323, Vol. 176, no 5, 625-637 p.Article in journal (Refereed) Published
Abstract [en]

Tilman's theory predicts the outcome of competition between two consumers sharing two resources on the basis of the shape of zero net-growth isoclines (ZNGIs). In his theory, intra-specific differences in resource use are not accounted for. Here we extend this theory to include situations where organisms undergo ontogenetic diet shifts, as these characterize the life histories of many species. In a situation that without diet shifts would lead to neutral coexistence of consumer species, we investigate whether ontogenetic diet shifts lead to niche partitioning. We analyze a model describing competition for two resources between two competitors with distinctive diets over ontogeny, using copepods (showing ontogenetic diet shifts) and daphnids (not showing ontogenetic diet shifts) as appropriate representatives. We show that an ontogenetic diet shift affects the shape of the ZNGI, changing it from reflecting perfectly substitutable resources to reflecting essential resources. Furthermore, we show that resource supply determines population stage structure and stage-dependent resource consumption in copepods and influences the competitive outcome with daphnids. In particular, we show that in itself, an ontogenetic diet shift can provide a competitive advantage if the supply of the adult resource is lower than the supply of the juvenile resource but that it always causes a disadvantage if the supply of the adult resource exceeds that of the juvenile resource.

Place, publisher, year, edition, pages
2010. Vol. 176, no 5, 625-637 p.
URN: urn:nbn:se:umu:diva-33441DOI: 10.1086/656488ISI: 000282369900011OAI: diva2:312454
Available from: 2010-04-24 Created: 2010-04-24 Last updated: 2011-02-23Bibliographically approved
In thesis
1. The effects of stage-specific differences in energetics on community structure
Open this publication in new window or tab >>The effects of stage-specific differences in energetics on community structure
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

When intraspecific individuals differ in resource intake, scramble competition occurs among inferior individuals growing food-dependently. Scramble can be released through predation mortality. As a consequence of this release, production rates in inferior individuals increase and biomass overcompensation in the subsequent life-stages may occur. When intraspecific individuals do not differ in their resource intakes biomass overcompensation does not occur. If an individual changes its resource intake over ontogeny, the balance of intake and losses, its energetics, will change over ontogeny. Furthermore, differences will arise between the energetics of different life-stages. The predominant volume of interspecific competition theory is based on studies assuming no stage-specific differences in energetics, neglecting the influence of ontogeny on community dynamics altogether. We study how an stage-specific differences in energetics affect expectations from conventional competition theory.

We use a stage-structured biomass model consistently translating individual life history processes, in particular food-dependent growth in body size, to the population level. The stage-structured population can be reduced to an unstructured population, if the energetics of all individuals are assumed to be equal.  The stage-structured model, however can also describe population dynamics when this equality is broken. We use the stage-structured biomass model to contrast the stage-specific differences resulting in a stage-structured population model, with an unstructured population model assuming no differences between stages.

We show that stage-specific differences in energetics can affect competition on various trophic levels. I: In stead of outcompeting each other, a predator can be facilitated by another preying a scrambling prey life-stage of the same prey population. II: In coexistence with their prey, omnivores with an ontogenetic diet shift, where juvenile omnivores feed on resource and adults on prey, affect community structure only as predators, not as competitors to their prey. We show coexistence of omnivore and prey is not possible if the dominating interaction is competition. Feeding on prey, however, alleviates competition with prey and facilitates the introduction of omnivores. III: An ontogenetic diet shift creates niche partitioning, where without it this would result in neutral coexistence of two consumers competing for two resources. IV: Furthermore, predators can change resource requirements of diet shifters such that diet shifters can reduce resources to lower equilibria and sustain higher predator biomass than consumers without stage-specific differences in energetics.

Place, publisher, year, edition, pages
Umeå: Department of Ecology and Environmental Science, Umeå University, 2010. 47 p.
ontogenetic diet shift, stage-structured biomass model, food-dependence, growth, development
National Category
Earth and Related Environmental Sciences Natural Sciences
Research subject
Earth Sciences with Specialization Environmental Analysis
urn:nbn:se:umu:diva-33444 (URN)978-91-7264-996-5 (ISBN)
Public defence
2010-05-24, KBC-huset , Lilla Hörsalen, KB3A9, Umeå universitet, Linneus väg 6, Umeå, 10:00 (English)
Available from: 2010-05-03 Created: 2010-04-24 Last updated: 2010-05-07Bibliographically approved

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