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Ontogenetic bottlenecks: effects on intraguild predation systems and ecosystem efficiency
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.ORCID iD: 0000-0002-0551-6896
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Umeå: Umeå University , 2015. , 29 p.
Keyword [en]
mixed interactions, cannibalism, life-history omnivory, ontogenetic niche shift, biomass overcompensation, biomass production, ontogenetic asymmetry, indirect effects
National Category
Ecology
Research subject
biology; Animal Ecology
Identifiers
URN: urn:nbn:se:umu:diva-105759ISBN: 978-91-7601-299-4 (print)OAI: oai:DiVA.org:umu-105759DiVA: diva2:846489
Public defence
2015-09-25, Lilla hörsalen (KB3A9), KBC-huset, Linnaeus väg 6, Umeå, 14:00 (English)
Opponent
Supervisors
Available from: 2015-09-04 Created: 2015-06-29 Last updated: 2015-09-02Bibliographically approved
List of papers
1. Habitat complexity does not promote coexistence in a size-structured intraguild predation system
Open this publication in new window or tab >>Habitat complexity does not promote coexistence in a size-structured intraguild predation system
2013 (English)In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 82, no 1, 55-63 p.Article in journal (Refereed) Published
Abstract [en]

Size-dependent interactions and habitat complexity have been identified as important factors affecting the persistence of intraguild predation (IGP) systems. Habitat complexity has been suggested to promote intraguild (IG) prey and intraguild predator coexistence through weakening trophic interactions particularly the predation link. Here, we experimentally investigate the effects of habitat complexity on coexistence and invasion success of differently sized IG-predators in a size-structured IGP system consisting of the IG-predator Poecilia reticulata and a resident Heterandria formosa IG-prey population. The experiments included medium-long and long-term invasion experiments, predator-prey experiments and competition experiments to elucidate the mechanisms underlying the effect of prey refuges. Habitat complexity did not promote the coexistence of IG-predator and IG-prey, although the predation link was substantially weakened. However, the presence of habitat structure affected the invasion success of large IG-predators negatively and the invasion success of small IG-predators positively. The effect of refuges on size-dependent invasion success could be related to a major decrease in the IG-predator's capture rate and a shift in the size distribution of IG-predator juveniles. In summary, habitat complexity had two main effects: (i) the predation link was diminished, resulting in a more competition driven system and (ii) the overall competitive abilities of the two species were equalized, but coexistence was not promoted. Our results suggest that in a size-structured IGP system, individual level mechanisms may gain in importance over species level mechanisms in the presence of habitat complexity.

Keyword
Coexistence, Competition, Omnivory, Ontogenetic niche shift, Predation, Refuges, Size-dependent interactions, Trophic interactions
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-66220 (URN)10.1111/j.1365-2656.2012.02032.x (DOI)000313752300007 ()
Available from: 2013-03-01 Created: 2013-02-18 Last updated: 2017-12-06Bibliographically approved
2. Predator life history affects persistence times of predators and consumers in an intraguild predation system
Open this publication in new window or tab >>Predator life history affects persistence times of predators and consumers in an intraguild predation system
(English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

Keyword
indirect effects, interaction strength, mixed predation-competition, multi-generation, trait variation
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-107024 (URN)
Available from: 2015-08-17 Created: 2015-08-17 Last updated: 2015-09-02
3. Exclusive juvenile predator resource promotes coexistence in a size-structured intraguild predation system
Open this publication in new window or tab >>Exclusive juvenile predator resource promotes coexistence in a size-structured intraguild predation system
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Coexistence in size-structured intraguild predation systems is limited, and is predicted to occur when the IG predator exhibits a complete ontogenetic niche shift, has a similar asymptotic size as the IG prey, or has access to an exclusive resource. Here we experimentally test the effect of a juvenile IG predator exclusive resource by mimicking an ontogenetic habitat shift in the IG predator that switched either to a more or a less productive habitat at maturity. We show that coexistence depends on relative habitat productivities when refuges are present and cannibalism in the IG predator is low, but does not so when refuges are absent and cannibalism in the IG predator is substantial. Overall compared to previous experimental studies without an ontogenetic habitat shift, we how that an exclusive resource for juvenile IG predators promotes coexistence with context-dependent differences in the manifestation of this effect. 

Keyword
population regulation, interaction strength, cannibalism, habitat complexity, life-history-omnivory, habitat productivity, ontogenetic habitat shift
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-107025 (URN)
Available from: 2015-08-17 Created: 2015-08-17 Last updated: 2015-09-02
4. Coexistence in a size-structured intraguild predation system promoted by an ontogenetic diet shift in the consumer
Open this publication in new window or tab >>Coexistence in a size-structured intraguild predation system promoted by an ontogenetic diet shift in the consumer
(English)Manuscript (preprint) (Other academic)
Abstract [en]

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. 

National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-107027 (URN)
Available from: 2015-08-17 Created: 2015-08-17 Last updated: 2015-09-02
5. Ontogenetic asymmetry modulates population biomass production and response to harvest
Open this publication in new window or tab >>Ontogenetic asymmetry modulates population biomass production and response to harvest
2015 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, 6441Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Nature Publishing Group, 2015
National Category
Ecology Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-103167 (URN)10.1038/ncomms7441 (DOI)000352633900025 ()25737320 (PubMedID)
Available from: 2015-05-27 Created: 2015-05-18 Last updated: 2017-12-04Bibliographically approved

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