Final Report Summary - METACOMBA (Factors regulating the composition of aquatic bacterial communities at the local scale)
Project summary
The distribution and abundance of species and the factors that control them are central to understanding and predicting ecosystem function and responses of communities and ecosystem to environmental change. The diversity and composition of any community is influenced by local factors, such as abiotic and biotic conditions; as well as regional factors, related to the dispersal of cells from the surrounding region or so-called'metacommunity'. Methodological advances during the last three decades have greatly increased our understanding of the diversity and turnover of natural bacterial communities, and also more recently, about the underlying assembly mechanisms, and we know that bacterial communities can be assembled by both local and regional factors. We know, however, very little about under which conditions the different mechanisms prevail, how their importance changes over time, in particular in response to environmental change and disturbances.
The project had two major aims: Firstly,we wanted to test which mechanisms prevail during the assembly of bacterial communities, how they differ between phylogenetic groups and how they change over time. Secondly, we wanted to test the effect of disturbances on bacterial diversity, community assembly mechanisms, particularly focusing on effects of disturbance strength, type and history and implications for ecosystem functioning.
These aims were addressed through a combination of field surveys using rock pools as models systems and experimental studies using microcosms and dialysis bags. In general, bacterial community composition was determined either by terminal restriction fragment length polymorphism analysis or 454 pyrosequencing of the 16S rRNA gene. In the experimental studies we also measured a variety of different functional parameters, e. g. respiration, biomass production and carbon substrate utilisation profiles.
Key results:
-Several factors interact during community assembly.
-The importance of local and regional factors for bacterial community composition varies between seasons depending on the productivity in the metacommunity. It further differs between phylogenetic groups depending on their niche breadth.
-Bacterial community composition and many functions change gradually along disturbance intensity and frequency gradients
-Top predators (Daphnia magna) decrease beta-diversity in bacterial metacommunities.
-Historical environmental condition play an important role in determining bacterial community composition
Conclusions:
The project significantly advances our understanding about the mechanisms that regulate the spatial as well as temporal turnover of bacterial communities, so-called beta-diversity. Beta-diversity among local communities increases with increasing productivity in the metacommunity, due to the increased relative importance of local factors. On the contrary, regional factors seem to be of particular importance during the initial assembly of communities and at times when dispersal among local communities is high. We could also clearly show that the different assembly mechanisms are not exclusive, but instead co-occur and shape bacterial communities simultaneously. The results from the project clearly demonstrate that future studies need to take temporal variability in abiotic factors into account and stresses the importance to further investigate what traits lead to the prevalence of different assembly mechanisms among sub-units of the entire bacterial community. Furthermore, our results draw attention to the multifaceted approach needed to understand the response of bacterial communities and ecosystem functions to disturbances and environmental change.
The distribution and abundance of species and the factors that control them are central to understanding and predicting ecosystem function and responses of communities and ecosystem to environmental change. The diversity and composition of any community is influenced by local factors, such as abiotic and biotic conditions; as well as regional factors, related to the dispersal of cells from the surrounding region or so-called'metacommunity'. Methodological advances during the last three decades have greatly increased our understanding of the diversity and turnover of natural bacterial communities, and also more recently, about the underlying assembly mechanisms, and we know that bacterial communities can be assembled by both local and regional factors. We know, however, very little about under which conditions the different mechanisms prevail, how their importance changes over time, in particular in response to environmental change and disturbances.
The project had two major aims: Firstly,we wanted to test which mechanisms prevail during the assembly of bacterial communities, how they differ between phylogenetic groups and how they change over time. Secondly, we wanted to test the effect of disturbances on bacterial diversity, community assembly mechanisms, particularly focusing on effects of disturbance strength, type and history and implications for ecosystem functioning.
These aims were addressed through a combination of field surveys using rock pools as models systems and experimental studies using microcosms and dialysis bags. In general, bacterial community composition was determined either by terminal restriction fragment length polymorphism analysis or 454 pyrosequencing of the 16S rRNA gene. In the experimental studies we also measured a variety of different functional parameters, e. g. respiration, biomass production and carbon substrate utilisation profiles.
Key results:
-Several factors interact during community assembly.
-The importance of local and regional factors for bacterial community composition varies between seasons depending on the productivity in the metacommunity. It further differs between phylogenetic groups depending on their niche breadth.
-Bacterial community composition and many functions change gradually along disturbance intensity and frequency gradients
-Top predators (Daphnia magna) decrease beta-diversity in bacterial metacommunities.
-Historical environmental condition play an important role in determining bacterial community composition
Conclusions:
The project significantly advances our understanding about the mechanisms that regulate the spatial as well as temporal turnover of bacterial communities, so-called beta-diversity. Beta-diversity among local communities increases with increasing productivity in the metacommunity, due to the increased relative importance of local factors. On the contrary, regional factors seem to be of particular importance during the initial assembly of communities and at times when dispersal among local communities is high. We could also clearly show that the different assembly mechanisms are not exclusive, but instead co-occur and shape bacterial communities simultaneously. The results from the project clearly demonstrate that future studies need to take temporal variability in abiotic factors into account and stresses the importance to further investigate what traits lead to the prevalence of different assembly mechanisms among sub-units of the entire bacterial community. Furthermore, our results draw attention to the multifaceted approach needed to understand the response of bacterial communities and ecosystem functions to disturbances and environmental change.