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Positive effects of mortality: biomass overcompensation in response to experimental culling
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
URN: urn:nbn:se:umu:diva-3123OAI: diva2:141599
Available from: 2008-04-29 Created: 2008-04-29 Last updated: 2010-01-14Bibliographically approved
In thesis
1. Alternative Stable States in Size-Structured Communities: Patterns, Processes, and Mechanisms
Open this publication in new window or tab >>Alternative Stable States in Size-Structured Communities: Patterns, Processes, and Mechanisms
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Alternative stable states have been, based on theoretical findings, predicted to be common in ecological systems. Empirical data from a number of laboratory and natural studies strongly suggest that alternative stable states also occur in real populations, communities and ecosystems. Potential mechanisms involve population size-structure and food-dependent individual development. These features can lead to ontogenetic niche shifts, juvenile recruitment bottlenecks and emergent Allee effects; phenomena that establish destabilising positive feedbacks in a system and hence create alternative stable states.

I studied the consequences of population size-structure for community dynamics at different scales of system complexity. I performed laboratory and ecosystem experiments. Small poecilliid fishes and planktonic invertebrates with short generation times and life spans were used as model organisms. This allowed me to assess the long-term dynamics of the populations and communities investigated.

The main experimental results are: (a) An ontogenetic niche shift in individuals of the phantom midge Chaoborus made the population vulnerable to an indirect competitive recruitment bottleneck imposed by cladoceran mesozooplankton via rotifers. Consequentially the natural zooplankton food web exhibited two alternative attractors. (b) Body size determined the success of Poecilia reticulata invading resident population of Heterandria formosa and thus the type of alternative stable state that established. Small invaders were outcompeted by the residents, whereas large invaders excluded their competitor by predating on its recruits. (c) External juvenile and adult mortality altered the internal feedback structure that regulates a laboratory population of H. formosa in such a way that juvenile biomass increased with mortality. This biomass overcompensation in a prey population can establish alternative stable states with top-predators being either absent or present.

The major conclusion is that size-structure and individual growth can indeed lead to alternative stable states. The considerations of these ubiquitous features of populations offer hence new insights and deeper understanding of community dynamics. Alternative stable states can have tremendous consequences for human societies that utilise the ecological services provided by an ecological system. Understanding the effects of size-structure on alternative stability is thus crucial for sustainable exploitation or production of food resources.

Place, publisher, year, edition, pages
Umeå: Ekologi, miljö och geovetenskap, 2008. 10 p.
biomass overcompensation, Chaoborus, emergent Allee effect, Heterandria formosa, juvenile recruitment bottlenecks, ontogenetic niche shifts, Poecilia reticulata
National Category
Biological Sciences
urn:nbn:se:umu:diva-1628 (URN)978-91-7264-499-1 (ISBN)
Public defence
2008-05-23, Lilla Hörsalen, KBC-Huset, SE-90187, Umeå, 13:00
Available from: 2008-04-29 Created: 2008-04-29Bibliographically approved

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