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Shifts in ecosystem functioning of a detritus-based foodweb explained by imbalances between resource and consumer stoichiometry
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Université de Toulouse.
Leibniz Institute of Freshwater Ecology and Inland Fisheries.
Swiss Federal Institute of Aquatic Science and Technology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The stoichiometric imbalance between consumers and resources can affect both resource processing rates and consumer growth, and thus constitutes a potentially important driver of ecosystem functioning. We hypothesized that imbalances in nitrogen (N), phosphorus (P), and carbon (C) concentrations between detritus and detritivores would have contrasting effects on two related ecosystem processes, with stronger imbalances triggering compensatory feeding while simultaneously constraining detritivore growth. In a stream field experiment, we found that growth of detritivores was constrained by stoichiometric imbalances mostly driven by N limitation, but there was no evidence for compensatory feeding. However, when offered diets of mixed litter with varying N:P and C:N, detritivores preferred the litter species showing the closest match to their own N:P and C:N, which drove accelerated processing of the preferred species in mixture. Our results highlight the role of stoichiometric imbalances between consumers and resources in regulating ecosystem processes.

Keyword [en]
Leaf litter decomposition, brown food web, N:P, threshold elemental ratio, degree of elemental mismatch
National Category
URN: urn:nbn:se:umu:diva-82909OAI: diva2:663889
Available from: 2013-11-13 Created: 2013-11-13 Last updated: 2013-11-13Bibliographically approved
In thesis
1. Ecosystem functioning in streams: Disentangling the roles of biodiversity, stoichiometry, and anthropogenic drivers
Open this publication in new window or tab >>Ecosystem functioning in streams: Disentangling the roles of biodiversity, stoichiometry, and anthropogenic drivers
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

What will happen to ecosystems if species continue to go extinct at the high rates seen today? Although ecosystems are often threatened by a myriad of physical or chemical stressors, recent evidence has suggested that the loss of species may have impacts on the functions and services of ecosystems that equal or exceed other major environmental disturbances. The underlying causes that link species diversity to ecosystem functioning include species niche complementarity, facilitative interactions, or selection effects, which cause process rates to be enhanced in more diverse communities. Interference competition, antagonistic interactions, or negative selection effects may otherwise reduce the efficiency or resource processing in diverse communities. While several of these mechanisms have been investigated in controlled experiments, there is an urgent need to understand how species diversity affects ecosystem functioning in nature, where variability of both biotic and abiotic factors is usually high. Species functional traits provide an important conceptual link between the effects of disturbances on community composition and diversity, and their ultimate outcomes for ecosystem functioning. Within this framework, I investigated relationships between the decomposition of leaf litter, a fundamental ecosystem process in stream ecosystems, and the composition and diversity of functional traits within the detritivore feeding guild. These include traits related to species habitat and resource preferences, phenology, and size. I focused on disentangling the biotic and abiotic drivers, including functional diversity, regulating ecosystem functioning in streams in a series of field experiments that captured real-world environmental gradients. Leaf decomposition rates were assessed using litter-bags of 0.5 and 10 mm opening size which allow the quantification of microbial and invertebrate + microbial contributions, respectively, to litter decomposition. I also used PVC chambers where leaf litter and a fixed number of invertebrate detritivores were enclosed in the field for a set time-period. The chemical characterisation of stream detritivores and leaf litter, by means of their nitrogen, phosphorus, and carbon concentration, was used to investigate how stoichiometric imbalance between detritivores and leaf litter may affect consumer growth and resource consumption. I found that the diversity and composition of functional traits within the stream detritivore feeding guild sometimes had effects on ecosystem functioning as strong as those of other major biotic factors (e.g. detritivore density and biomass), and abiotic factors (e.g. habitat complexity and agricultural stressors). However, the occurrence of diversity-functioning relationships was patchy in space and time, highlighting ongoing challenges in predicting the role of diversity a priori. The stoichiometric imbalance between consumers and resource was also identified as an important driver of functioning, affecting consumer growth rates, but not leaf decomposition rates. Overall, these results shed light on the understanding of species functional diversity effect on ecosystems, and indicate that the shifts in the functional diversity and composition of consumer guilds can have important outcomes for the functioning of stream ecosystems.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2013. 44 p.
detrital food web, functional diversity, stoichiometry, nitrogen and phosphorus concentrations, recalcitrant carbon, spatial and temporal species distribution, pools and riffles, isotopes, leaf decomposition rates, land use, restoration, habitat complexity
National Category
urn:nbn:se:umu:diva-82914 (URN)978-91-7459-758-5 (ISBN)
Public defence
2013-12-06, BiA401 i Biologihuset, Umeå universitet, Umeå, 09:30 (English)
Swedish Research Council, 621-2006-375
Available from: 2013-11-15 Created: 2013-11-13 Last updated: 2013-11-19Bibliographically approved

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