| 1. |
- Reichstein, Birte, 1983-, et al.
(author)
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Coexistence in a size-structured intraguild predation system promoted by an ontogenetic diet shift in the consumer
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Other publication (other academic/artistic)abstract
- In life history omnivore (IGP) systems coexistence between omnivore and consumer at high productivity has only been demonstrated when the omnivore undergoes a complete ontogenetic niche shift at or before maturity from feeding on the shared resource to feeding on the consumer. Here we investigate the effects of an exclusive resource for juvenile consumers on coexistence between omnivore and consumer. We demonstrate that an alternative resource for juvenile consumers allows for coexistence between omnivore and consumer species even when the adult omnivore feeds on the shared resource to a substantial extent. Coexistence is promoted by a strong niche separation in the consumer and when the productivity of the shared resource is high relative to the juvenile consumer exclusive resource. At high shared resource productivity coexistence is promoted by either a low or a high niche separation in the omnivore. In general our results suggest that for coexistence to occur at high productivities a strong life-history separation in resource use is necessary in either the consumer or the omnivore. Strong life-history separation in the omnivore results in predation driven coexistence, while strong life-history separation in the consumer results in competitive coexistence.
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| 2. |
- Reichstein, Birte, 1983-, et al.
(author)
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Ontogenetic asymmetry modulates population biomass production and response to harvest
- 2015
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In: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 6
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Journal article (peer-reviewed)abstract
- Patterns in biomass production are determined by resource input (productivity) and trophic transfer efficiency. At fixed resource input, variation in consumer biomass production has been related to food quality, metabolic type and diversity among species. In contrast, intraspecific variation in individual body size because of ontogenetic development, which characterizes the overwhelming majority of taxa, has been largely neglected. Here we show experimentally in a long-term multigenerational study that reallocating constant resource input in a two-stage consumer system from an equal resource delivery to juveniles and adults to an adult-biased resource delivery is sufficient to cause more than a doubling of total consumer biomass. We discuss how such changes in consumer stage-specific resource allocation affect the likelihood for alternative stable states in harvested populations as a consequence of stage-specific overcompensation in consumer biomass and thereby the risk of catastrophic collapses in exploited populations.
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| 3. |
- Reichstein, Birte, 1983-
(author)
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Ontogenetic bottlenecks : effects on intraguild predation systems and ecosystem efficiency
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Size-dependent differences between individuals in size-structured organisms have fundamental effect on population and community dynamics. Intraguild predation (IGP) is one specifically interesting constellation that often arises when two size-structured populations interact. Ontogenetic bottlenecks that determine population size-structure are affected by both population intrinsic as well as population extrinsic factors, and are therefore context-dependent. Surprisingly, size-structured IGP systems have mainly been investigated theoretically and especially long-term empirical studies are widely lacking. In this thesis I investigate empirically how habitat complexity, interaction strength, and stage-specific resource availabilities affect population processes and their effects on the dynamics of a size-structured IGP system. I conducted multi-generation experiments in a size-structured IGP system, with the Least Killifish (Heterandria formosa) as IG prey and the Common Guppy (Poecilia reticulata) as IG predator. With no alternative resource next to the shared resource, IG predator and IG prey could not coexist. Weak interactions only increased IG prey and IG predator persistence times and observed exclusion patterns depended on habitat complexity. An alternative resource for either the juvenile IG predator or the juvenile IG prey on the other hand promoted coexistence. However, this coexistence was context-dependent. Ontogenetic bottlenecks played a central role in the dynamics of the size-structured IGP system in general. In the final study I show that an ontogenetic bottleneck can, through changes in stage-specific resource availabilities, be affected in a way that leads to increased trophic transfer efficiency with potential effects on higher trophic levels.Overall, the results emphasize importance of the broader context in which size-structured communities are embedded. Especially, when managing natural communities it is important to account for the combined effects of size-structure, stage-specific resource availabilities, and habitat structure. Specifically, when managing species that connect habitats or ecosystems all life-stages’ environmental conditions must be consider in order to ensure strong predictive power of tools used for ecosystem management planning.
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| 4. |
- Reichstein, Birte, 1983-, et al.
(author)
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Predator life history affects persistence times of predators and consumers in an intraguild predation system
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Other publication (other academic/artistic)abstract
- Complex habitats and thereby weaker predator-prey interactions have been suggested to promote coexistence between predator and prey in intraguild predation (IGP) systems. For a size-structured IGP system spatial refuges have been shown to weaken interactions but not to promote coexistence. Spatial refuges however also affect the spatial distribution of small and large individuals. Here we report the results of a multi-generation laboratory experiment where we manipulated interaction strength by using the same IG predator (Common guppy, Poecilia reticulata) but a population with a different life-history evolution and lower predation voracity. Resident IG prey (Least Killifish, Heterandria formosa) were invaded by large or small IG predators, invasion success was recorded. Compared to the invasion by more voracious IG predator individuals, weaker predation per se (no refuges) did not affect invasion success but did increase IG prey and IG predator persistence times. Compared to the invasion by more voracious IG predator individuals in the presence of refuges, weaker predation per se (no refuges) resulted in similar persistence times but different invasion success. We conclude that the effect on community dynamics depends on the context in which weak interactions are realized. Both spatial refuges and life-history differences affected predation strength and competitive relationships quantitatively but only when spatial refuges were present was this quantitative change coupled to qualitative changes in species interactions. Though under stable environmental conditions in our experiment coexistence did not occur we argue that in temporarily or spatially variable systems weak interactions have the potential to promote coexistence by prolonging IG predator and IG prey persistence times.
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| 5. |
- Schröder, Arne, 1974-, et al.
(author)
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Invasion success depends on invader body size in a size-structured mixed predation-competition system
- 2009
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In: Journal of Animal Ecology. - : John Wiley & Sons, Inc. - 0021-8790 .- 1365-2656. ; 78:6, s. 1152-1162
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Journal article (peer-reviewed)abstract
- 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.
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