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Species interactions and energy transfer in aquatic food webs
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. (Marine Ecology)
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Food webs are structured by intricate nodes of species interactions which govern the flow of organic matter in natural systems. Despite being long recognized as a key component in ecology, estimation of food web functioning is still challenging due to the difficulty in accurately measuring species interactions within a food web. Novel tracing methods that estimate species diet uptake and trophic position are therefore needed for assessing food web dynamics.

The focus of this thesis is the use of compound specific nitrogen and carbon stable isotopes and molecular techniques for assessing predator-prey interactions and energy flow in natural aquatic ecosystems, with a particular focus on the species links between phytoplankton and zooplankton.

The use of δ15N amino acid values to predict organism trophic position are evaluated through a meta-analysis of available literature which included measurements from 359 marine species (article I). Through a controlled feeding study isotope incorporation in aquatic organisms, across both plant-animal and animal-animal species linkages is further assessed (article II).

These studies showed that δ15N amino acid values are useful tools for categorizing animal trophic position. Organism feeding ecology influenced nitrogen trophic discrimination (difference in isotope ratio between consumer and diet), with higher discrimination in herbivores compared to omnivores and carnivores (article I). Nitrogen isotope trophic discrimination also varied among feeding treatments in the laboratory study (article II). The combined findings from articles I & II suggest that researchers should consider using group specific nitrogen trophic discrimination values to improve accuracy in species trophic position predictions. 

Another key finding in the controlled laboratory study (article II) was consistently low carbon isotope discrimination in essential amino acids across all species linkages, confirming that these compounds are reliable dietary tracers.

The δ13C ratios of essential amino acids were applied to study seasonal dynamics in zooplankton resource use in the Baltic Sea (article III). Data from this study indicated that zooplankton assimilate variable resources throughout the growing season. Molecular diet analysis (article IV) showed that marine copepod and cladoceran species ingested both autotrophic and heterotrophic resources.

Evidence from both articles III & IV also revealed that zooplankton feed on a relatively broad range of diet items but not opportunistically on all available food sources. Mesozooplankton feeding patterns suggested that energy and nutritional flows were channelled through an omnivorous zooplankton food web including microzooplankton prey items. Overall the results of this thesis highlight that stable isotope ratios in specific compounds and molecular techniques are useful tracing approaches that improve our understanding of food web functioning.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University , 2015. , 40 p.
Keyword [en]
Aquatic food webs, zooplankton, stable isotope analysis amino acids, molecular diet analysis
National Category
Ecology
Research subject
Marine Ecology
Identifiers
URN: urn:nbn:se:su:diva-123600ISBN: 978-91-7649-316-8 (print)OAI: oai:DiVA.org:su-123600DiVA: diva2:875089
Public defence
2016-01-26, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 10:00 (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 4: Manuscript.

 

Available from: 2015-12-30 Created: 2015-11-30 Last updated: 2016-01-04Bibliographically approved
List of papers
1. Meta-analysis of amino acid stable nitrogen isotope ratios for estimating trophic position in marine organisms
Open this publication in new window or tab >>Meta-analysis of amino acid stable nitrogen isotope ratios for estimating trophic position in marine organisms
2015 (English)In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 178, no 3, 631-642 p.Article in journal (Refereed) Published
Abstract [en]

Estimating trophic structures is a common approach used to retrieve information regarding energy pathways, predation, and competition in complex ecosystems. The application of amino acid (AA) compound-specific nitrogen (N) isotope analysis (CSIA) is a relatively new method used to estimate trophic position (TP) and feeding relationships in diverse organisms. Here, we conducted the first meta-analysis of delta N-15 AA values from measurements of 359 marine species covering four trophic levels, and compared TP estimates from AA-CSIA to literature values derived from food items, gut or stomach content analysis. We tested whether the AA trophic enrichment factor (TEF), or the N-15 enrichment among different individual AAs is constant across trophic levels and whether inclusion of delta N-15 values from multiple AAs improves TP estimation. For the TEF of glutamic acid relative to phenylalanine (Phe) we found an average value of 6.6 aEuro degrees across all taxa, which is significantly lower than the commonly applied 7.6 aEuro degrees. We found that organism feeding ecology influences TEF values of several trophic AAs relative to Phe, with significantly higher TEF values for herbivores compared to omnivores and carnivores, while TEF values were also significantly lower for animals excreting urea compared to ammonium. Based on the comparison of multiple model structures using the metadata of delta N-15 AA values we show that increasing the number of AAs in principle improves precision in TP estimation. This meta-analysis clarifies the advantages and limitations of using individual delta N-15 AA values as tools in trophic ecology and provides a guideline for the future application of AA-CSIA to food web studies.

Keyword
Compounds-specific isotope analysis, Food webs, Trophic enrichment factor, Trophic ecology
National Category
Biological Sciences
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-119142 (URN)10.1007/s00442-015-3305-7 (DOI)000356534400001 ()
Available from: 2015-07-31 Created: 2015-07-29 Last updated: 2017-12-04Bibliographically approved
2. Amino acid stable isotope discrimination in diverse aquatic food chains
Open this publication in new window or tab >>Amino acid stable isotope discrimination in diverse aquatic food chains
2015 (English)Manuscript (preprint) (Other academic)
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-124337 (URN)
Available from: 2015-12-18 Created: 2015-12-18 Last updated: 2015-12-18Bibliographically approved
3. Seasonal dynamics of zooplankton resource use revealed by carbon amino acid stable isotope values
Open this publication in new window or tab >>Seasonal dynamics of zooplankton resource use revealed by carbon amino acid stable isotope values
2015 (English)In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 531, 143-154 p.Article in journal (Refereed) Published
Abstract [en]

Reliable tracer techniques are fundamental to retrieving accurate information on consumer dietary resource use in dynamic ecosystems. Analysis of delta C-13 values in essential amino acids has shown great promise in effectively capturing consumer food sources, since essential amino acids are not synthesized by heterotrophic organisms but instead routed directly from dietary sources to consumers, resulting in negligible C-13 trophic discrimination. We assessed seasonal feeding patterns of a widespread key copepod species (Acartia spp.) in the northern Baltic proper using complementary approaches: bulk delta C-13 and delta N-15 values, delta C-13 values of essential amino acids, and quantitative phytoplankton taxonomic data. Our results showed distinct differences between Acartia and seston delta C-13 essential amino acid values measured at weekly to monthly sampling intervals, which indicated that Acartia preferentially utilized specific dietary resources that comprised only parts of the total phytoplankton composition (varying from 19.7% to 81.4% during the season). Results also indicated that care should be taken when inferring trophic position from bulk stable isotopes when consumers are highly selective, since isotope values of seston may not accurately reflect consumer specific diet resource uptake. Analysis of delta C-13 values in essential amino acids was shown to be a promising tool to accurately trace consumer resource use in complex natural systems.

Keyword
Stable isotopes, Amino acids, Acartia, Zooplankton, Phytoplankton, Food webs
National Category
Biological Sciences Earth and Related Environmental Sciences
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-120098 (URN)10.3354/meps11319 (DOI)000358445000010 ()
Available from: 2015-09-03 Created: 2015-09-01 Last updated: 2017-12-04Bibliographically approved
4. Marine zooplankton diet preferences across species, life stages and seasons using DNA barcoding
Open this publication in new window or tab >>Marine zooplankton diet preferences across species, life stages and seasons using DNA barcoding
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Research subject
Marine Ecology
Identifiers
urn:nbn:se:su:diva-124339 (URN)
Available from: 2015-12-18 Created: 2015-12-18 Last updated: 2015-12-18Bibliographically approved

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