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The influence of trophic polymorphisms on habitat coupling in aquatic food webs
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology. School of Biological Sciences and The Environment Institute, University of Adelaide, North Terrace, SA 5005, Australia.ORCID iD: 0000-0003-3505-7077
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Trophic cascades, together with other indirect interactions are important aspects in shaping the composition and abundance of species in the food web. Theoretically, movement of energy between systems, and coupling between habitats by mobile predators have been suggested as being important for food web stability and evenness. Individual diet specialisations have been shown to be widespread in many animal taxa. Although not widely studied, some studies have indicated that mobile predators that display individual specialisations, may have a reduced ability to couple habitats.

In this thesis, by using field studies and an experimental study, my aim was to assess the individual specialisation displayed by Eurasian perch (Perca fluviatilis) and its influence on the ability of the perch to couple habitats. In the experiment, we also investigated the effect of habitat coupling, or the lack of habitat coupling, on the dynamics and stability of the resources in the ecosystem.

We show that habitat diversity and resource availability influenced perch individual specialisation and morphological variation. We found that the perch total niche width decreased with decreasing habitat switching ability. We demonstrate asymmetrical habitat coupling ability in perch across pelagic and littoral habitats, providing evidence that not all individuals within a species respond in the same way when it comes to spatial coupling and thereby providing stability within a food web.

Our results expand on previous work and suggest that habitat coupling ability can influence individual specialisations and niche width. Furthermore, we show the importance of individual specialisations in relation to habitat coupling. Finally, we provide evidence for the theory that a food web dominated by a food specialist should exhibit more variable resource dynamics than a food web dominated by a generalist predator by showing a greater indirect effect of predation on the phytoplankton levels when no habitat coupling occurs. While many models and theoretical concepts have proposed a stabilising effect of cross movement of energy and mobile predators, little empirical evidence exists that confirms this mechanism.

In conclusion, my thesis gives some support for the theoretical predictions that habitats coupled by a generalist predator should be more stable.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , 41 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214
National Category
Ecology
Research subject
Biology with specialization in Limnology
Identifiers
URN: urn:nbn:se:uu:diva-315720ISBN: 978-91-554-9826-9 (print)OAI: oai:DiVA.org:uu-315720DiVA: diva2:1075438
Public defence
2017-04-07, Friessalen, Evolutionsbiologiskt centrum (EBC), Norbyvägen 14, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-03-17 Created: 2017-02-20 Last updated: 2017-03-20
List of papers
1. The influence of habitat accessibility on the dietary and morphological specialisation of an aquatic top predator
Open this publication in new window or tab >>The influence of habitat accessibility on the dietary and morphological specialisation of an aquatic top predator
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(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-315718 (URN)
Available from: 2017-02-20 Created: 2017-02-20 Last updated: 2017-02-20
2. Habitat coupling mediates trophic cascades in an aquatic community
Open this publication in new window or tab >>Habitat coupling mediates trophic cascades in an aquatic community
(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-315717 (URN)
Available from: 2017-02-20 Created: 2017-02-20 Last updated: 2017-02-20
3. Combining resource use assessment techniques reveals trade-offs in trophic specialization of polymorphic perch
Open this publication in new window or tab >>Combining resource use assessment techniques reveals trade-offs in trophic specialization of polymorphic perch
2016 (English)In: Ecosphere, ISSN 2150-8925, E-ISSN 2150-8925, Vol. 7, no 8, e01387Article in journal (Refereed) Published
Abstract [en]

Trophic polymorphism has found to be common in many taxa and is a suggested mechanism of ecological speciation. To characterize the trophic linkages of specific morphotypes of organisms as well as a time-integrated niche use, several methods are available. In this study, we present data of multiple techniques to investigate the trophic divergence of Eurasian perch (Perca fluviatilis) that displays well-studied trophic polymorphism associated with littoral and pelagic habitats in lakes. We combined bulk stable isotope and fatty acid analyses on the muscle tissue of perch from three different lakes in Sweden with analyses of stomach content. By comparing the three methods, we aimed at providing a broad and highly resolved picture on the trophic divergence in freshwater fish. The degree in morphological divergence varied between perch caught in the three different lakes. Generally, perch caught in the pelagic zone were more streamlined compared to the ones caught in the littoral zone that had a deeper body, as shown by geometric morphometrics. The three diet assessment methods revealed different levels of information. Data on stomach content showed some preferences for specific dietary items in littoral and pelagic perch, but general trophic specialization could not be concluded due to the small sample size. Analyses of delta C-13 and delta N-15, however, confirmed these results as a long-term pattern connected to specific habitat use in two of the three lakes. Fatty acid signatures of perch reflected partly those of the prey items of the specific habitats. Although the proportions of the essential fatty acid 22:6n-3 were lower in littoral resources, the proportions in littoral fish were similar to the ones caught in the pelagic zone. We concluded that although a fundamental contribution from littoral resources exists in littoral phenotypes, a minor reliance on pelagic prey items is obviously needed to provide essential compounds. Thus, by combining the methods to characterize direct resource use (i.e., stomach analyses) with others that utilize trophic biomarkers (i.e., analyses of stable isotopes and fatty acids), we were able to illustrate the degree of variation in trophic divergence of perch but also shed some light on potential trade-offs that are related to resource specialization in freshwater fish.

Keyword
carbon stable isotopes; ecological speciation; fatty acid analysis; geometric morphometrics; Perca fluviatilis; resource polymorphism; Special Feature; Biomarkers in Trophic Ecology; stomach content analysis
National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-264657 (URN)10.1002/ecs2.1387 (DOI)000387208900001 ()
Available from: 2015-10-15 Created: 2015-10-15 Last updated: 2017-02-20Bibliographically approved
4. Asymmetrical habitat coupling of a top predator
Open this publication in new window or tab >>Asymmetrical habitat coupling of a top predator
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(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-315719 (URN)
Available from: 2017-02-20 Created: 2017-02-20 Last updated: 2017-02-20

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