Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Ecosystem functioning in streams: Disentangling the roles of biodiversity, stoichiometry, and anthropogenic drivers
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
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.
Keyword [en]
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
Ecology
Identifiers
URN: urn:nbn:se:umu:diva-82914ISBN: 978-91-7459-758-5 (print)OAI: oai:DiVA.org:umu-82914DiVA: diva2:663924
Public defence
2013-12-06, BiA401 i Biologihuset, Umeå universitet, Umeå, 09:30 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 621-2006-375
Available from: 2013-11-15 Created: 2013-11-13 Last updated: 2013-11-19Bibliographically approved
List of papers
1. No evidence for functional litter diversity effects on litter decomposition, fungal decomposers and nutrient immobilization
Open this publication in new window or tab >>No evidence for functional litter diversity effects on litter decomposition, fungal decomposers and nutrient immobilization
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Biodiversity and ecosystem functioning theory suggests that litter mixtures composed of dissimilar leaf species can enhance decomposition due to species trait complementarity. Here we create a continuous gradient of litter chemistry trait variability within species mixtures to assess effects of litter dissimilarity on three related processes in a natural stream: litter decomposition, fungal biomass accrual in the litter, and nitrogen and phosphorus immobilization. Litter from a pool of eight leaf species was analyzed for chemistry traits affecting decomposition (lignin, nitrogen, and phosphorus) and assembled in all of the 28 possible two-species combinations. Litter dissimilarity was characterized in terms of a range of functional diversity measures, using Euclidean and Gower distances and dendrogram-based indices. Despite favorable experimental conditions for litter dissimilarity effects to arise, we found no significant relationships between decomposition rate of individual leaf species and litter functional dissimilarity, irrespective of whether decomposition was mediated by microbes alone or by both microbes and litter-consuming invertebrates. Likewise, no effects of functional dissimilarity emerged on either fungal biomass accrual or changes during decomposition of nitrogen or phosphorus concentrations in individual leaf species. These results provide support for the contention that litter diversity effects on decomposition in streams are less pronounced than in forest environments, and in particular are less common than effects on terrestrial primary productivity. Key to understanding these discrepancies may be the constant supply of nutrients provided by the flowing water in streams, exacerbated by very large-scale cultural nutrient enrichment of surface waters in many parts of the world.

Keyword
biodiversity and ecosystem functioning, functional plant litter traits, detritus breakdown, ergosterol fungal biomass, nitrogen immobilization, phosphorus dynamics
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-82898 (URN)
Available from: 2013-11-13 Created: 2013-11-13 Last updated: 2014-04-16Bibliographically approved
2. Shifts in ecosystem functioning of a detritus-based foodweb explained by imbalances between resource and consumer stoichiometry
Open this publication in new window or tab >>Shifts in ecosystem functioning of a detritus-based foodweb explained by imbalances between resource and consumer stoichiometry
Show others...
(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
Leaf litter decomposition, brown food web, N:P, threshold elemental ratio, degree of elemental mismatch
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-82909 (URN)
Available from: 2013-11-13 Created: 2013-11-13 Last updated: 2013-11-13Bibliographically approved
3. When does diversity matter?: Species functional diversity and ecosystem functioning across habitats and seasons in a field experiment
Open this publication in new window or tab >>When does diversity matter?: Species functional diversity and ecosystem functioning across habitats and seasons in a field experiment
2014 (English)In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 83, no 2, 460-469 p.Article in journal (Refereed) Published
Abstract [en]

Despite ample experimental evidence indicating that biodiversity might be an important driver of ecosystem processes, its role in the functioning of real ecosystems remains unclear. In particular, the understanding of which aspects of biodiversity are most important for ecosystem functioning, their importance relative to other biotic and abiotic drivers, and the circumstances under which biodiversity is most likely to influence functioning in nature, is limited. We conducted a field study that focussed on a guild of insect detritivores in streams, in which we quantified variation in the process of leaf decomposition across two habitats (riffles and pools) and two seasons (autumn and spring). The study was conducted in six streams, and the same locations were sampled in the two seasons. With the aid of structural equations modelling, we assessed spatiotemporal variation in the roles of three key biotic drivers in this process: functional diversity, quantified based on a spe- cies trait matrix, consumer density and biomass. Our models also accounted for variability related to different litter resources, and other sources of biotic and abiotic variability among streams. All three of our focal biotic drivers influenced leaf decomposition, but none was important in all habitats and seasons. Functional diversity had contrasting effects on decomposition between habitats and seasons. A positive relationship was observed in pool habitats in spring, associated with high trait dispersion, whereas a negative relationship was observed in riffle habitats during autumn. Our results demonstrate that functional biodiversity can be as significant for functioning in natural ecosystems as other important biotic drivers. In particular, variation in the role of functional diversity between seasons highlights the importance of fluctuations in the relative abundances of traits for ecosystem process rates in real ecosystems.

Place, publisher, year, edition, pages
John Wiley & Sons, 2014
Keyword
stream ecosystems, litter decomposition, species evenness, species traits, spatial-temporal variability, path analyses
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-82868 (URN)10.1111/1365-2656.12142 (DOI)000331469200015 ()
Funder
Swedish Research Council, 621-2006-375
Available from: 2013-11-12 Created: 2013-11-12 Last updated: 2017-12-06Bibliographically approved
4. Shifts in the diversity and composition of consumer traits limit the effects of land use on stream ecosystem functioning
Open this publication in new window or tab >>Shifts in the diversity and composition of consumer traits limit the effects of land use on stream ecosystem functioning
(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
response and effect trait, functional diversity, biodiversity, leaf litter decomposition
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-82910 (URN)
Available from: 2013-11-13 Created: 2013-11-13 Last updated: 2013-11-13Bibliographically approved
5. Is ecosystem functioning enhanced when habitat complexity increases?: River restoration and the functioning of algal and detrital food webs
Open this publication in new window or tab >>Is ecosystem functioning enhanced when habitat complexity increases?: River restoration and the functioning of algal and detrital food webs
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Stream restoration is a multi-million dollar business that aims at rehabilitating systems impacted by hydrogeomorphological modifications, such as channelization, and ameliorating physical or ecological degradation caused by catchment-scale impacts, such as agriculture or urbanization. Despite extensive programs aimed at restoring habitat complexity in channelized streams, there is little evidence for a recovery of biological diversity, and functional responses have been little assessed. Notably large-scale habitat restorations have recently been undertaken in a river catchment in northern Sweden, including rehabilitation of large habitat structures (massive boulders, large woody debris) originally removed to facilitate timber floating. Based on a hydrogeomorphological measure of habitat complexity, we characterised variability in habitat complexity across 20 stream reaches in the catchment, including reference, channelised and restored sites. We assessed whether increased habitat complexity following restoration affected retention of organic matter (FPOM), the functional diversity and organisation of the detritivore feeding guild, and two ecosystem processes: algal productivity and litter decomposition. Deposition of FPOM increased along the complexity gradient, as did leaf litter decomposition mediated by invertebrates. The increase in invertebrate-mediated decomposition was associated with shifts in the functional composition of detritivore assemblages, with feeding traits associated with more efficient decomposition more prominent in the restored reaches. There was no change in algal productivity at local scales, but increases in shallow, well- lit habitats favourable for algal growth indicate a possible increase in algal productivity at the stream reach scale. Increases in habitat complexity enhanced functioning within the detritital foodweb at local scales, without any changes in the biodiversity of detritivores. Our findings indicate that aspects of functional diversity and ecosystem functioning may be better than measures of community structure for assessing stream restoration projects.

Keyword
Biodiversity, restoration assessments, functional diversity, functional dispersion, leaf litter decomposition, algal production, FPOM retention and deposition
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-82911 (URN)
Available from: 2013-11-13 Created: 2013-11-13 Last updated: 2013-11-13Bibliographically approved

Open Access in DiVA

Ecosystem functioning in streams(4052 kB)1153 downloads
File information
File name FULLTEXT01.pdfFile size 4052 kBChecksum SHA-512
156dbc4e31d85233282eefda332e67d7bd70e73954c59b677a92834c7b85c23a2519923f742e8955672a67b2cdd5bf2d30f4b9cbf355c40c5ac9c2eb68ecae5a
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Frainer, André
By organisation
Department of Ecology and Environmental Sciences
Ecology

Search outside of DiVA

GoogleGoogle Scholar
Total: 1153 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 980 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf