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Assembly Mechanisms in Aquatic Bacterial Communities: The Role of Disturbances, Dispersal and History
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Environmental conditions, biotic interactions, dispersal and history have been suggested to be important processes influencing the spatial distribution of organisms and thus to affect community assembly. Understanding how these processes influence community assembly is important, particularly because community diversity and composition are suggested to be relevant for ecosystem functioning. Moreover, bacteria are strongly contributing to nutrient and carbon cycle. Bacteria are highly abundant and ubiquitous, and thus it is relevant to study how they are assembled. This thesis aims to gain insight on the role of these processes on aquatic bacterial community assembly, diversity and functioning. The studies included in this thesis involve transplant and microcosm experiments performed in the lab as well as manipulation experiments and field surveys in a natural rock pool systems. Bacterial community composition was addressed by analysis of 16S rRNA gene and community functioning by measuring bacterial production, community respiration and the ability to use different carbon substrates. This thesis highlights that species sorting is a very important assembly mechanism for bacterial communities, but also finds that other processes such as dispersal and history contribute to the patterns observed. Dispersal caused rescuing effects compensating for losses of diversity; at the same time it increased the similarity between communities. Moreover, bacteria have shown a high level of functional plasticity when colonizing a new locality. Interestingly, past environmental conditions explained the structure of bacterial communities better than present-day environmental conditions. Disturbances and biotic interactions are also important in the assembly of communities. Disturbance caused temporary shifts in bacterial function and changes in composition, the magnitude of which depended on the intensity and the frequency of the disturbance. However, natural aquatic bacterial communities showed quite high resilience capacities. Competition can shift the proportion of generalists and specialists species whereas predation or trophic interactions have been found to decrease diversity and to modify the importance of stochasticity. Both caused alterations of community functioning. Finally, this thesis shows that the diversity-functioning relationship is context dependent. Further research should be directed to understanding the intensity and direction of changes in composition and how this affects the functionality of bacterial communities

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. , 56 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1071
Keyword [en]
diversity, community composition, metacommunity
National Category
Ecology Microbiology
Identifiers
URN: urn:nbn:se:uu:diva-207183ISBN: 978-91-554-8749-2 (print)OAI: oai:DiVA.org:uu-207183DiVA: diva2:647107
Public defence
2013-10-25, Friessalen, Evolutionary Biology Centre (EBC), Norbyvägen 18, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2013-10-02 Created: 2013-09-10 Last updated: 2014-01-23
List of papers
1. Effects of Disturbance Intensity and Frequency on Bacterial Community Composition and Function
Open this publication in new window or tab >>Effects of Disturbance Intensity and Frequency on Bacterial Community Composition and Function
2012 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 7, no 5, e36959- p.Article in journal (Refereed) Published
Abstract [en]

Disturbances influence community structure and ecosystem functioning. Bacteria are key players in ecosystems and it is therefore crucial to understand the effect of disturbances on bacterial communities and how they respond to them, both compositionally and functionally. The main aim of this study was to test the effect of differences in disturbance strength on bacterial communities. For this, we implemented two independent short-term experiments with dialysis bags containing natural bacterial communities, which were transplanted between ambient and 'disturbed' incubation tanks, manipulating either the intensity or the frequency of a salinity disturbance. We followed changes in community composition by terminal restriction fragment analysis (T-RFLP) and measured various community functions (bacterial production, carbon substrate utilization profiles and rates) directly after and after a short period of recovery under ambient conditions. Increases in disturbance strength resulted in gradually stronger changes in bacterial community composition and functions. In the disturbance intensity experiment, the sensitivity to the disturbance and the ability of recovery differed between different functions. In the disturbance frequency experiment, effects on the different functions were more consistent and recovery was not observed. Moreover, in case of the intensity experiment, there was also a time lag in the responses of community composition and functions, with functional responses being faster than compositional ones. To summarize, our study shows that disturbance strength has the potential to change the functional performance and composition of bacterial communities. It further highlights that the overall effects, rates of recovery and the degree of congruence in the response patterns of community composition and functioning along disturbance gradients depend on the type of function and the character of the disturbance.

National Category
Biological Sciences
Identifiers
urn:nbn:se:uu:diva-177625 (URN)10.1371/journal.pone.0036959 (DOI)000305339400046 ()
Available from: 2012-07-18 Created: 2012-07-17 Last updated: 2017-12-07Bibliographically approved
2. Testing responses of bacterial communities to environmental change using whole ecosystem manipulation experiments
Open this publication in new window or tab >>Testing responses of bacterial communities to environmental change using whole ecosystem manipulation experiments
(English)Manuscript (preprint) (Other academic)
National Category
Ecology Microbiology
Identifiers
urn:nbn:se:uu:diva-207179 (URN)
Available from: 2013-09-10 Created: 2013-09-10 Last updated: 2014-05-08
3. Mechanisms determining the fate of dispersed bacterial communities in new environments
Open this publication in new window or tab >>Mechanisms determining the fate of dispersed bacterial communities in new environments
2013 (English)In: ISME Journal, ISSN 1751-7362, Vol. 7, no 1, 61-71 p.Article in journal (Refereed) Published
Abstract [en]

Recent work has shown that dispersal has an important role in shaping microbial communities. However, little is known about how dispersed bacteria cope with new environmental conditions and how they compete with local resident communities. To test this, we implemented two full-factorial transplant experiments with bacterial communities originating from two sources (freshwater or saline water), which were incubated, separately or in mixes, under both environmental conditions. Thus, we were able to separately test for the effects of the new environment with and without interactions with local communities. We determined community composition using 454-pyrosequencing of bacterial 16S rRNA to specifically target the active fraction of the communities, and measured several functional parameters. In absence of a local resident community, the net functional response was mainly affected by the environmental conditions, suggesting successful functional adaptation to the new environmental conditions. Community composition was influenced both by the source and the incubation environment, suggesting simultaneous effects of species sorting and functional plasticity. In presence of a local resident community, functional parameters were higher compared with those expected from proportional mixes of the unmixed communities in three out of four cases. This was accompanied by an increase in the relative abundance of generalists, suggesting that competitive interactions among local and immigrant taxa could explain the observed functional overachievement. In summary, our results suggest that environmental filtering, functional plasticity and competition are all important mechanisms influencing the fate of dispersed communities.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-192014 (URN)10.1038/ismej.2012.80 (DOI)000313236000006 ()
Available from: 2013-01-24 Created: 2013-01-15 Last updated: 2014-01-23Bibliographically approved
4. The spatial structure of bacterial communities is influenced by historical environmental conditions
Open this publication in new window or tab >>The spatial structure of bacterial communities is influenced by historical environmental conditions
2014 (English)In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 95, no 5, 1134-1140 p.Article in journal (Refereed) Published
Abstract [en]

The spatial structure of ecological communities, including that of bacteria, is often influenced by species sorting by contemporary environmental conditions. Moreover, historical processes, i.e., ecological and evolutionary events that have occurred at some point in the past, such as dispersal limitation, drift, priority effects, or selection by past environmental conditions, can be important, but are generally investigated much less. Here, we conducted a field study using 16 rock pools, where we specifically compared the importance of past vs. contemporary environmental conditions for bacterial community structure by correlating present differences in bacterial community composition among pools to environmental conditions measured on the same day, as well as to those measured 2, 4, 6, and 8 d earlier. The results prove that selection by past environmental conditions exists, since we were able to show that bacterial communities are, to a greater extent, an imprint of past compared to contemporary environmental conditions. We suggest that this is the result of a combination of different mechanisms, including priority effects that cause rapid adaptation to new environmental conditions of taxa that have been initially selected by past environmental conditions, and slower rates of turnover in community composition compared to environmental conditions.

National Category
Ecology Microbiology
Identifiers
urn:nbn:se:uu:diva-207181 (URN)10.1890/13-1300.1 (DOI)000336740500003 ()
Available from: 2013-09-10 Created: 2013-09-10 Last updated: 2017-12-06Bibliographically approved
5. Effects of predation and dispersal on the diversity an functioning of bacterial metacommunities
Open this publication in new window or tab >>Effects of predation and dispersal on the diversity an functioning of bacterial metacommunities
(English)Manuscript (preprint) (Other academic)
National Category
Ecology Microbiology
Identifiers
urn:nbn:se:uu:diva-207177 (URN)
Available from: 2013-09-10 Created: 2013-09-10 Last updated: 2014-01-23

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