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Shifts in the diversity and composition of consumer traits limit the effects of land use on stream ecosystem functioning
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
SLU Uppsala.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Abiotic disturbances that directly affect ecosystem functioning may also affect the distribution and composition of functional traits within a community. Shifts in trait composition may further enhance or even limit those effects caused by the abiotic stressors. In this work we asked whether an agricultural landuse gradient would affect both invertebrate detritivore functional diversity and leaf litter decomposition in streams. We further asked how the landuse effect on functional traits would relate to ecosystem functioning, and if their relationship would change across seasons. Using Structural Equation Modelling, which allows the partitioning of both direct and indirect relationships, we show that in the autumn land use had a positive effect on functioning, but this relationship was counteracted by a negative indirect effect on leaf decomposition. Landuse positively affected the presence of detritivore traits that were negatively related to functioning and also promoted trait dominance, which was negatively related to functioning. These results contrast with direct linear regressions between disturbance and functioning, which did not yield any relationship between the two variables. In spring, landuse had no effect on functioning, which is explained by the reduced impact of agricultural disturbances in our boreal streams. Our results emphasise the key role played by trait identity and diversity in mediating the effects of human disturbance on ecosystem functioning. Furthermore, our findings highlight the value of distinguishing the direct effects of human disturbances on ecosystem processes from those mediated through changes in the structure of trophic webs.

Keyword [en]
response and effect trait, functional diversity, biodiversity, leaf litter decomposition
National Category
URN: urn:nbn:se:umu:diva-82910OAI: diva2:663890
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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