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Aquifer microbial community assembly:do neutral processes dominate?
Presenter: Michael Strack (@mixtrak)
MQ SupervisorsGrant HoseAdam StowDavid Nipperess
UTS supervisorJohn Ellis
Structure1. Background – Groundwater & community ecology
2. Project overview
3. Evidence for dispersal limitation
4. Evidence for environmental selection
5. Conclusions & current work
Chand Baori, Rajasthan
Chennai, Tamil NaduWe rely on groundwater
Global liquid freshwater(Shiklomanov, 1998)
Groundwater Everything else
Wetlands rely on groundwater
Microbes regulate water quality
Processes structuring communities?
Theory of Community Ecology (TOCE)(Vellend, 2010)
Sampling design
Water chemistry & flora
ArchaeaBacteriaFungiEukarya generally
~
Dispersal limitation
Sampling design
~
Hypothesis• More DOC, higher richnessApproachMultiple linear regression (MLR): richness vs.• Total organic carbon (TOC)• Inorganic carbon (IC)• Nitrate (NO3)• Dissolved oxygen (DO)• Salinity (conductivity, “cond”)• Depth to water table (water.table)
If not dispersal, what about selection? (sensu Vellend)
Environmental structuring – richness MLRn = 36
Taxon Model p Adjusted R2Predictor variablesp < 0.05 (*), p < 0.01 (**), p < 0.001 (***)
Archaea < 0.001 0.5665 +NO3***, +cond**, -water.table***
Bacteria 0.001 0.2755 -IC**
Fungi 0.013 0.2016 -TOC**
Eukarya n.s. n.s. n.s.
Aggregate 0.016 0.1412 -TOC*
Compositional similarityHypothesis• More similar environments = more similar communities
Approach• Distance-based redundancy analysis• Multivariate extension of linear regression• How much variation in response variables is explained by predictors?• Response = matrix of Jaccard distances of communities (i.e. dissimilarity
matrix)• Predictors = environmental variables + region (factor) + richness• Constrained (canonical) ordination – significance testing etc.
Archaeap = 0.006R2 = 0.05
Bacteriap = 0.001R2 = 0.12
Fungip = 0.001R2 = 0.14
Eukaryap = 0.001R2 = 0.15
Summary
• Richness• Catchment
Taxon IC TOC NO3 Conductivity
Archaea + ++ +
Bacteria ++ +
Fungi ++ + +
Eukarya ++
Conclusions• Models significant (p < 0.01) BUT low R2 (< 0.16)• Experimental power? N = 36
OR
Selection & dispersal limitation weak forces in GW?• Oligotrophic - selection slow relative to other processes• Functional redundancy (i.e. small fitness differences)• Sparse populations & limited selective interactions• Resilience: metabolic flexibility, dormancy, resistant structures• Environmental stability, niche construction, refugia, micro-habitats Neutral ecosystem?
Current work
Thank you
Acknowledgements• Supervisors: Grant Hose, Adam Stow, David Nipperess, John Ellis• WRS: Martin Anderson, Peter Graham• Funding: ARC/MQ• Mentoring & molbio: Paulsen & Emma V labs
@mixtrak