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Bottom-up and top-down regulation of heterogeneous lake food webs
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Food webs are networks of organisms linked by trophic interactions that regulate the responses of ecosystems to environmental change. Such regulation is a result of the effects of resources on the abundance of their consumers (i.e. bottom-up effects) and/or the influence of consumers on the abundance of their resources (i.e. top-down effects). Lake food webs comprise pelagic and benthic production pathways and are largely affected by fluxes of resources from/to adjacent terrestrial ecosystems. These pathways are often coupled by mobile generalist consumers, potentially leading to indirect interactions among prey that arise when sharing a predator. In contrast, consumers can also undergo resource specialization that restricts their ability to couple resources at a given time.

In this thesis, I observed that top-down control of predators on benthic and pelagic prey at increasing productivity was highly dependent on apparent mutualism that was driven by switching behaviour of generalist fish. That, in addition to bottom-up responses of benthic pathways at increasing productivity, had important consequences for the fluxes of energy and high quality polyunsaturated fatty acids (PUFAs) to terrestrial systems via insect emergence. I also found that PUFAs were highly regulated over the ontogeny of Eurasian perch (Perca fluviatilis). Mismatches with PUFA composition in prey may in turn affect resource specialization and the timing of ontogenetic diet shifts, altering the role of perch in the food web. Finally, browning, which is a phenomenon affecting many temperate and boreal lakes, did not affect bottom-up and top-down control in open-water lake food webs. Instead, browning affected prey selectivity, probably changing the pathways of energy transfer within the open-water food web. Overall, this thesis demonstrates that predictions of food web responses in lake ecosystems and their exports to adjacent terrestrial systems depend on the coupling of different pathways and subsequent indirect interactions among prey through shared predation. This could not be explained by classic food chain theory, but rather by a framework including resource coupling and resource specialization over the ontogeny of consumers. These observations must not be overlooked when constructing a comprehensive model of food webs across time and space.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2020. , p. 67
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1906
Keywords [en]
food webs, resource coupling, ontogenetic diet shifts, resource specialization, bottom-up, top-down, browning, eutrophication, lake, mesocosms, fatty acids, apparent competition
National Category
Ecology
Research subject
Biology with specialization in Limnology
Identifiers
URN: urn:nbn:se:uu:diva-404190ISBN: 978-91-513-0876-0 (print)OAI: oai:DiVA.org:uu-404190DiVA, id: diva2:1393580
Public defence
2020-04-03, Ekmansalen, Norbyvägen 18, Uppsala, 13:00 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation, KAW 2013.0091Available from: 2020-03-10 Created: 2020-02-17 Last updated: 2020-03-26Bibliographically approved
List of papers
1. Regulation of fatty acid composition related to ontogenetic changes and niche differentiation of a common aquatic consumer
Open this publication in new window or tab >>Regulation of fatty acid composition related to ontogenetic changes and niche differentiation of a common aquatic consumer
2020 (English)In: Article in journal (Refereed) Submitted
National Category
Ecology
Research subject
Biology with specialization in Limnology
Identifiers
urn:nbn:se:uu:diva-404183 (URN)
Available from: 2020-02-14 Created: 2020-02-14 Last updated: 2020-02-19
2. Fatty acid accumulation in feeding types of a natural freshwater fish population
Open this publication in new window or tab >>Fatty acid accumulation in feeding types of a natural freshwater fish population
2020 (English)In: Article in journal (Refereed) Submitted
National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-404188 (URN)
Available from: 2020-02-14 Created: 2020-02-14 Last updated: 2020-02-19
3. Short-term apparent mutualism drives responses of aquatic prey at increasing productivity
Open this publication in new window or tab >>Short-term apparent mutualism drives responses of aquatic prey at increasing productivity
2020 (English)In: Article in journal (Refereed) Submitted
Abstract [en]

According to apparent competition theory, sharing a predator should cause indirect interactions among prey that can substantially influence food-web responses to environmental drivers. However, empirical evidence of apparent competition under ongoing environmental change is still scarce. In an 8-week mesocosm experiment, we found that short-term responses of aquatic food webs to increasing productivity were strongly regulated by apparent mutualism between benthic and pelagic prey in the presence of a generalist fish. Following trends in natural systems, increasing productivity in our mesocosms favored the relative abundance of benthic prey. This elicited a shift in fish selectivity from pelagic to benthic prey driven by fish switching behavior which resulted in lower and delayed top-down control on pelagic prey. Our results highlight that apparent competition theory may explain food-web responses across environmental gradients, whereby resulting prey dynamics and stability may highly depend on the foraging behavior exhibited by generalist predators.

Keywords
Apparent competition, top-down control, trophic cascade, food web, resource coupling, eutrophication, indirect interactions, crucian carp, mesocosm
National Category
Ecology
Research subject
Biology with specialization in Limnology; Biology with specialization in Animal Ecology
Identifiers
urn:nbn:se:uu:diva-404054 (URN)
Funder
Knut and Alice Wallenberg Foundation, KAW 2013.0091
Available from: 2020-02-08 Created: 2020-02-08 Last updated: 2020-02-25Bibliographically approved
4. The emergence of fatty acids—Aquatic insects as vectors along a productivity gradient
Open this publication in new window or tab >>The emergence of fatty acids—Aquatic insects as vectors along a productivity gradient
Show others...
2020 (English)In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 65, no 3, p. 565-578Article in journal (Refereed) Published
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-404062 (URN)
Available from: 2020-02-08 Created: 2020-02-08 Last updated: 2020-02-17Bibliographically approved
5. Disentangling the effects of carbon fluxes and shading inherent to terrestrial DOC on lake food webs
Open this publication in new window or tab >>Disentangling the effects of carbon fluxes and shading inherent to terrestrial DOC on lake food webs
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-404186 (URN)
Available from: 2020-02-14 Created: 2020-02-14 Last updated: 2020-02-19

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