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Impact of food quality on aquatic consumers: Behavioral and physiological adjustments
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Food quantity and quality together determine growth rates of consumers and the utilisation efficiencies of available resources in aquatic and terrestrial ecosystems. The effect of food quality on the performance of consumers is dependent on both, its direct influence on ingestion and assimilation rates, and on the behavioural and physiological adjustments of consumers to their food environment. The main target of this thesis was to investigate the nature and scope of behavioural and physiological adjustments in consumers and assess the resulting consequences for consumers’ fitness and ecosystem-wide nutrient flows.

In paper I, we investigated the extent of elemental homeostasis across several taxonomic groups of planktonic herbivores. We found that adjustments in elemental ratios (C:N:P) in body tissues are an important physiological response of heterotrophic flagellates, but that in ciliates and multi-cellular organisms C:N:P ratios varied much less than in their algal prey. Hence, alternative regulatory mechanisms determine the reactions of metazoan zooplankton to decreases in food quality. In paper II, we developed a theoretical model to explore regulation in behaviour and digestive physiology of consumers to changes in the food environment. Our results demonstrate that feeding and digestion of consumers are determined by trade-offs between benefits and costs of investments in these processes. We revealed that the flexibility in consumers’ behaviour and physiology had strong influences on assimilation rates and efficiencies and thereby affected growth rates and a wide range of ecosystem functions. In paper III, we investigated the scope and consequences of adjustments in feeding and assimilation rates of copepods exposed to different diets. An important finding was that consumers can use resources, which are available in surplus, to increase the uptake of a limiting nutrient. Such nutrient interconversion led to co-limitation, the simultaneous limitation of copepods by two different nutrients. Finally, in paper IV, we aimed to test the effect of food quality on population dynamics in the field. We investigated zooplankton populations in tropical soda-lakes, an environment with a surplus of planktonic food sources that thus provides an ideal setting for investigations of food quality. However, we found that the hatching of resting eggs from lake sediments was the main driver of zooplankton bloom formation resulting in non-cyclical dynamics that were not related to food quality.

These findings contributed to our understanding under which circumstance and by which mechanisms food quality affects the performance of consumers. My results highlight that food quality has not only direct effects on consumers’ growth but also triggers behavioral and physiological responses in consumers to maximize their fitness.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University , 2016. , 39 p.
National Category
Ecology
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-128828ISBN: 978-91-7649-403-5 (print)OAI: oai:DiVA.org:su-128828DiVA: diva2:917019
Public defence
2016-05-24, P216, NPQ-huset, Svante Arrhenius väg 20 A, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript.

Available from: 2016-04-29 Created: 2016-04-05 Last updated: 2017-02-17Bibliographically approved
List of papers
1. Stoichiometric regulation in micro- and mesozooplankton
Open this publication in new window or tab >>Stoichiometric regulation in micro- and mesozooplankton
2015 (English)In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 37, no 2, 293-305 p.Article in journal (Refereed) Published
Abstract [en]

Aquatic ecosystems experience large natural variation in elemental composition of carbon (C), nitrogen (N) and phosphorus (P), which is further enhanced by human activities. Primary producers typically reflect the nutrient ratios of their resource, whose stoichiometric composition can vary widely in conformity to environmental conditions. In contrast, C to nutrient ratios in consumers are largely constrained within a narrow range, termed homeostasis. In comparison to crustacean zooplankton, less is known about the ability of protozoan grazers and rotifer species to maintain stoichiometric balance. In this study, we used laboratory experiments with a primary producer (Nannochloropsis sp.), three different species of protozoan grazers and one mesozooplankton species: two heterotrophic dinoflagellates (Gyrodinium dominans and Oxyrrhis marina), a ciliate (Euplotes sp.) and a rotifer (Brachionus plicatilis) to test the stoichiometric response to five nutrient treatments. We showed that the dependency of zooplankton C: N: P ratios on C: nutrient ratios of their food source varies among species. Similar to the photoautotroph, the two heterotrophic dinoflagellates weakly regulated their internal stoichiometry. In contrast, the strength of stoichiometric regulation increased to strict homeostasis in both the ciliate and the rotifer, similar to crustacean zooplankton. Our study further shows that ciliate and rotifer growth can be constrained by imbalanced resource supply. It also indicates that these key primary consumers have the potential to trophically upgrade poor stoichiometric autotrophic food quality for higher trophic levels.

Keyword
homeostasis, nutrient limitation, heterotrophic dinoflagellate, ciliate, rotifer
National Category
Biological Sciences
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-117010 (URN)10.1093/plankt/fbu109 (DOI)000352487600003 ()
Note

AuthorCount:3;

Available from: 2015-05-06 Created: 2015-05-05 Last updated: 2017-12-04Bibliographically approved
2. Trade-offs in governing consumers’ responses to food quality and quantity variation
Open this publication in new window or tab >>Trade-offs in governing consumers’ responses to food quality and quantity variation
(English)Manuscript (preprint) (Other academic)
National Category
Biological Sciences
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-128819 (URN)
Available from: 2016-04-05 Created: 2016-04-05 Last updated: 2016-04-22Bibliographically approved
3. Nutrient deficiencies and the limits of physiological regulation in copepods
Open this publication in new window or tab >>Nutrient deficiencies and the limits of physiological regulation in copepods
(English)Manuscript (preprint) (Other academic)
National Category
Biological Sciences
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-128818 (URN)
Available from: 2016-04-05 Created: 2016-04-05 Last updated: 2017-08-14Bibliographically approved
4. Benthic-pelagic coupling drives non-seasonal zooplankton blooms and restructures energy flows in shallow tropical lakes
Open this publication in new window or tab >>Benthic-pelagic coupling drives non-seasonal zooplankton blooms and restructures energy flows in shallow tropical lakes
Show others...
2016 (English)In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 61, no 3, 795-805 p.Article in journal (Refereed) Published
Abstract [en]

Zooplankton blooms are a frequent phenomenon in tropical systems. However, drivers of bloom formation and the contribution of emerging resting eggs are largely unexplored. We investigated the dynamics and the triggers of rotifer blooms in African soda-lakes and assessed their impact on other trophic levels. A meta-analysis of rotifer peak densities including abundances of up to 6 × 105 individuals L−1 demonstrated that rotifer bloom formation was uncoupled from the food environment and the seasonality of climatic conditions. A time series with weekly sampling intervals from Lake Nakuru (Kenya) revealed that intrinsic growth factors (food quality and the physicochemical environment) significantly affected rotifer population fluctuations, but were of minor importance for bloom formation. Instead, rotifer bloom formation was linked to sediment resuspension, a prerequisite for hatching of resting-eggs. Population growth rates exceed pelagic birth rates and simulations of rotifer dynamics confirmed the quantitative importance of rotifer emergence from the sediment egg-bank and signifying a decoupling of bloom formation from pelagic reproduction. Rotifer blooms led to a top-down control of small-sized algae and facilitated a switch to more grazing-resistant, filamentous cyanobacteria. This shift in phytoplankton composition cascaded up the food chain and triggered the return of filter-feeding flamingos. Calculations of consequent changes in the lake's energy budget and export of aquatic primary production to terrestrial ecosystems demonstrated the large potential impact of nonseasonal disturbances on the functioning of shallow tropical lakes.

National Category
Biological Sciences
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-128817 (URN)10.1002/lno.10241 (DOI)000375748400001 ()
Available from: 2016-04-05 Created: 2016-04-05 Last updated: 2017-11-30Bibliographically approved

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