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Alternative Stable States in Size-Structured Communities: Patterns, Processes, and Mechanisms
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
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.
Keyword [en]
biomass overcompensation, Chaoborus, emergent Allee effect, Heterandria formosa, juvenile recruitment bottlenecks, ontogenetic niche shifts, Poecilia reticulata
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:umu:diva-1628ISBN: 978-91-7264-499-1 (print)OAI: oai:DiVA.org:umu-1628DiVA: diva2:141600
Public defence
2008-05-23, Lilla Hörsalen, KBC-Huset, SE-90187, Umeå, 13:00
Opponent
Supervisors
Available from: 2008-04-29 Created: 2008-04-29Bibliographically approved
List of papers
1. Direct experimental evidence for alternative stable states: a review
Open this publication in new window or tab >>Direct experimental evidence for alternative stable states: a review
2005 (English)In: Oikos, ISSN 0030-1299, Vol. 110, no 1, 3-19 p.Article in journal (Refereed) Published
Abstract [en]

A large number of studies have presented empirical arguments for the existence of alternative stable states (ASS) in a wide range of ecological systems. However, most of these studies have used non-manipulative, indirect methods, which findings remain open for alternative explanations. Here, we review the direct evidence for ASS resulting from manipulation experiments. We distinguish four conclusive experimental approaches which test for predictions made by the hysteresis effect: (1) discontinuity in the response to an environmental driving parameter, (2) lack of recovery potential after a perturbation, (3) divergence due to different initial conditions and (4) random divergence. Based on an extensive literature search we found 35 corresponding experiments. We assessed the ecological stability of the reported contrasting states using the minimum turnover of individuals in terms of life span and classified the studies according to 4 categories: (1) experimental system, (2) habitat type, (3) involved organisms and (4) theoretical framework. 13 experiments have directly demonstrated the existence of alternative stable states while 8 showed the absence of ASS in other cases. 14 experiments did not fulfil the requirements of a conclusive test, mostly because they applied a too short time scale. We found a bias towards laboratory experiments compared to field experiments in demonstrating bistability. There was no clear pattern of the distribution of ASS over categories. The absence of ASS in 38% of the tested systems indicates that ASS are just one possibility of how ecological systems can behave. The relevance of the concept of ASS for natural systems is discussed, in particular under consideration of the observed laboratory bias, perturbation frequency and variable environments. It is argued, that even for a permanently transient system, alternative attractors may still be of relevance.

Identifiers
urn:nbn:se:umu:diva-3120 (URN)10.1111/j.0030-1299.2005.13962.x (DOI)
Available from: 2008-04-29 Created: 2008-04-29 Last updated: 2009-07-02Bibliographically approved
2. Alternative zooplankton community attractors revealed in a whole-lake perturbation experiment
Open this publication in new window or tab >>Alternative zooplankton community attractors revealed in a whole-lake perturbation experiment
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Identifiers
urn:nbn:se:umu:diva-3121 (URN)
Available from: 2008-04-29 Created: 2008-04-29 Last updated: 2010-01-14Bibliographically approved
3. Invasion success depends on invader body size in a size-structured mixed predation-competition system
Open this publication in new window or tab >>Invasion success depends on invader body size in a size-structured mixed predation-competition system
Show others...
2009 (English)In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 78, no 6, 1152-1162 p.Article in journal (Refereed) Published
Abstract [en]

1. The size of an individual is an important determinant of its trophic position and the type of interactions it engages in with other heterospecific and conspecific individuals. Consequently an individual's ecological role in a community changes with its body size over ontogeny, leading to that trophic interactions between individuals are a size-dependent and ontogenetically variable mixture of competition and predation.

2. Because differently sized individuals thus experience different biotic environments, invasion success may be determined by the body size of the invaders. Invasion outcome may also depend on the productivity of the system as productivity influences the biotic environment.

3. In a laboratory experiment with two poeciliid fishes the body size of the invading individuals and the daily amount of food supplied were manipulated.

4. Large invaders established persistent populations and drove the resident population to extinction in 10 out of 12 cases, while small invaders failed in 10 out of 12 trials. Stable coexistence was virtually absent. Invasion outcome was independent of productivity.

5. Further analyses suggest that small invaders experienced a competitive recruitment bottleneck imposed on them by the resident population. In contrast, large invaders preyed on the juveniles of the resident population. This predation allowed the large invaders to establish successfully by decreasing the resident population densities and thus breaking the bottleneck.

6. The results strongly suggest that the size distribution of invaders affects their ability to invade, an implication so far neglected in life-history omnivory systems. The findings are further in agreement with predictions of life-history omnivory theory, that size-structured interactions demote coexistence along a productivity gradient.

Place, publisher, year, edition, pages
John Wiley & Sons, Inc, 2009
Keyword
coexistence, competitive recruitment bottleneck, life-history omnivory, ontogenetic niche shift, productivity gradient
Identifiers
urn:nbn:se:umu:diva-3122 (URN)10.1111/j.1365-2656.2009.01590.x (DOI)
Available from: 2008-04-29 Created: 2008-04-29 Last updated: 2010-09-24Bibliographically approved
4. Positive effects of mortality: biomass overcompensation in response to experimental culling
Open this publication in new window or tab >>Positive effects of mortality: biomass overcompensation in response to experimental culling
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Identifiers
urn:nbn:se:umu:diva-3123 (URN)
Available from: 2008-04-29 Created: 2008-04-29 Last updated: 2010-01-14Bibliographically approved

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