In the Light of Evolution Volume II: Biodiversity and Extinction (2008) / Chapter Skim
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8 Resistance, Resilience, and Redundancy in Microbial Communities--STEVEN D. ALLISON and JENNIFER B. H. MARTINY
8 Resistance, Resilience, and Redundancy in Microbial Communities--STEVEN D. ALLISON and JENNIFER B. H. MARTINY
Pages 149-166
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From page 149... ...
Other studies demonstrate that changes in composition are often associated with changes in ecosystem process rates. Thus, changes in microbial communi ties due to disturbance may directly affect ecosystem processes.
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From page 150... ...
. As a result, the abundance, diversity, and interactions of microorganisms are often assumed to be unimportant to ecosystem processes, particularly in terrestrial ecosystem models.
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From page 151... ...
The model is used to illustrate how empirical data could be used to predict microbial process rates under disturbance, even for relatively diverse communities. Because it is not feasible to add a parameter for each microbial population in a community, we consider when coarse information about microbial composition, such as the relative abundance of a few key clades within a functional group, could help decrease uncertainty about predictions of ecosystem processes.
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From page 152... ...
These traits and others associated with microbes -- such as high abundances, widespread dispersal, and the potential for rapid growth rates -- have also led to the suggestion that microbial communities will be resilient to change (Fenchel and TABLE 8.1 Summary of Definitions Used in This Chapter Term Definition Functional group All organisms that directly contribute to the rate of a particular functional process in an ecosystem Functional redundancy The ability of one microbial taxon to carry out a process at the same rate as another under the same environmental conditions Functional similarity The ability of two microbial communities to carry out a functional process at a similar rate, regardless of differences in composition Microbial composition The richness, relative abundance, and phylogenetic structure of taxa in an assemblage Microbial taxon A group of phylogenetically related microbes Resilience The rate at which microbial composition returns to its original composition after being disturbed Resistance The degree to which microbial composition remains unchanged in the face of a disturbance Physiological trait A physiological characteristic that determines the contribution of a microbial taxon to a functional process Physiological response curve The function describing the relationship between the process contribution of a microbial taxon and disturbance intensity
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From page 153... ...
Alternatively, if the community is sensitive and does change, it could be resilient and quickly recover to its initial composition. Finally, a community whose FIGURE 8.1 A schematic of how disturbance can change microbial composition and thereby affect ecosystem processes versus when disturbance would not have this effect (when the microbial community is resistant, resilient, or functionally redundant)
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From page 154... ...
Only if community composition is sensitive to a disturbance, not resilient, and functionally dissimilar to the original community do changes in community composition matter for predicting ecosystem process rates. In addition, the degree to which a community is resistant, resilient, and functionally similar will influence the degree to which community composition matters to a particular process.
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From page 155... ...
Papers from this search included studies that targeted composition broadly such as with phospholipid fatty acid analysis, which targets bacteria and fungi. In contrast, other studies examine narrower functional guilds within the Bacteria by PCR-amplifying a functional gene followed by a fingerprinting technique (such as denaturing gradient gel electrophoresis or terminal restriction fragment length polymorphism)
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From page 156... ...
Thus, even if the relative abundance of some taxa decreased initially, these taxa might physiologically acclimate to the new abiotic conditions over time and return to their original abundance. Finally, if physiological adaptation is not possible, then the rapid evolution (through mutations or horizontal gene exchange)
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From page 157... ...
FUNCTIONAL REDUNDANCY OF MICROBIAL COMPOSITION Our literature survey clearly indicates that microbial communities are sensitive to disturbance and often do not rapidly recover to their original state. These responses beg the question of whether compositional shifts will affect ecosystem processes -- will the disturbed community be functionally similar to the original community?
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From page 158... ...
A number of approaches can be used to disentangle compositional versus environmental effects on ecosystem processes. In one approach, process rates are measured before and after a disturbance manipulation but before microbial composition changes.
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From page 159... ...
They transplanted soil microbial communities across a climate gradient and demonstrated that community composition affected process rates independent of climate. Furthermore, they used phospholipid fatty acid data to correlate process rates with specific members of the microbial community and concluded that nitrification potential and N2O flux were likely driven by Gram-negative bacteria.
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From page 160... ...
, then we can define these communities as functionally similar, although they may contain taxa that are not functionally redundant. To predict how microbial processes will respond to disturbance, we also need to know the physiological responses of each taxon to disturbance.
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From page 161... ...
Given that microbial composition is usually assessed with phylogenetic markers, this information could be used to predict how members of a functional group influence ecosystem process rates. As an illustration of this approach, consider the functional group in Fig.
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H Martiny FIGURE 8.3 A stylized illustration comparing the phylogenetic relationship of physiological traits versus process responses to disturbance among taxa.
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From page 163... ...
Then, predictions of process rates could be estimated based on the abundances of relatively broad phylogenetic groups. However, we currently lack the empirical evidence necessary to establish which microbial processes show a strong correspondence between phylogeny and physiology.
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From page 164... ...
of different taxa, we note that changes in body size distributions within or across taxonomic groups could also affect ecosystem process rates as suggested by metabolic scaling theory (Enquist et al., 2003)
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From page 165... ...
Although this hypothesis is currently difficult to test, recent studies suggest that the taxa in many microbial communities are probably not functionally redundant and different communities are not functionally similar. How can the information that microbial composition affects ecosystem functioning be used to improve predictions of ecosystem process rates under disturbance?
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From page 166... ...
Greater efforts toward improving culture techniques and assessing the physiological responses of microbial populations under controlled conditions would be especially useful. Once explicitly incorporated into models, this information could greatly enhance our ability to predict ecosystem responses to global change.
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