In the Light of Evolution Volume II: Biodiversity and Extinction (2008) / Chapter Skim
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7 Microbes on Mountainsides: Contrasting Elevational Patterns of Bacterial and Plant Diversity--JESSICA A. BRYANT, CHRISTINE LAMANNA, HÉLÈNE MORLON, ANDREW J. KERKHOFF, BRIAN J. ENQUIST, and JESSICA L. GREEN
7 Microbes on Mountainsides: Contrasting Elevational Patterns of Bacterial and Plant Diversity--JESSICA A. BRYANT, CHRISTINE LAMANNA, HÉLÈNE MORLON, ANDREW J. KERKHOFF, BRIAN J. ENQUIST, and JESSICA L. GREEN
Pages 127-148
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From page 127... ...
Although elevational patterns of plant and animal diversity have been studied for centuries, such pat terns have not been reported for microorganisms and remain poorly understood. Here, in an effort to assess the generality of elevational diversity patterns, we examined soil bacterial and plant diversity along an elevation gradient.
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From page 128... ...
. Elevational diversity studies that consider empirical patterns of macroorganisms and microorganisms in parallel are needed to provide a more unified framework for understanding diversity patterns in Earth's major environmental gradients and predicting systemwide ecological responses to climatic change.
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From page 129... ...
Here, in an effort to assess the generality of elevational diversity patterns and the forces that structure these patterns, we quantified both plant and soil bacterial diversity patterns along an elevational gradient in the Colorado Rocky Mountains. A parsimonious hypothesis is that if the forces structuring biodiversity across the gradient are the same for bacteria and plants, then the resulting taxon and phylogenetic biogeographic patterns will be similar for both groups.
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From page 130... ...
Assuming phylogenetic niche conservatism, phylogenetic clustering within a local assemblage is considered consistent with the hypothesis that selective filters (e.g., environmental conditions) cause local assemblages to comprise closely related taxa (Webb et al., 2002)
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lineages that are shared but ultimately lead to unshared taxa. One can test whether the phylogenetic similarity between two communities is solely a consequence of compositional similarity, or if it is also caused by a nonrandom structure of shared and unshared lineages.
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, whereas angiosperm richness and phylogenetic diversity patterns are hump-shaped (regression analysis, r2 = 0.53, PJBryant_Figure1_bw.tif respectively)
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Given the parsimonious hypothesis that closely related taxa are more ecologically similar (i.e., phylogenetic niche conservatism) , our results suggest that abiotic filtering tends to be a more prominent force in the structuring of bacterial communities along the gradient.
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From page 134... ...
Although our study was not designed to directly examine the environmental drivers of elevational diversity patterns, our results do illuminate their potential role in shaping biodiversity patterns across the gradient. The contrasting phylogenetic diversity patterns we observed in plants and microbes suggest a differing role in how abiotic forces structure communities across the gradient.
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. The slope of the decay of phylogenetic similarity between Acidobacteria communities is significantly steeper than predicted by a null model constrained by the decrease in taxon turnover (solid gray circles)
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0.132 –0.311* 0.030 –0.0001 0.116 –0.0009 phylogenetic diversity Plant phylogenetic 0.473*
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TABLE 7.2 Mantel Correlations Between Community and Environmental Similarities % % % Elevation Temperature pH Slope Aspect Nitrogen Carbon Moisture Acidobacteria compositional –0.57*
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Sampling bacteria at a spatial scale that more closely approaches the ‘‘ecologically equivalent'' grain of plants may result in convergent biodiversity patterns between these two groups. Taxonomic scale also influences biodiversity patterns.
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. To our knowledge the influence of sampling effort on phylogenetic biodiversity patterns has not been explored.
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FIGURE 7.5 Microbial NRI and NTI values across the elevational gradient at four different taxonomic resolutions. Observed community phylogenetic structures chance (P < 0.05)
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phylogenetic similarity of Acidobacteria communities at four taxonomic resolutions. The compositional and phylogenetic similarity between Acidobacteria communities significantly decreases with increasing elevational separation (Mantel test, P < 0.001)
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From page 142... ...
These data had a 15.24-cm resolution per pixel and a horizontal accuracy of 60–90 cm. Characterization of Acidobacteria Communities with 16S Clone Libraries At each site, the bacterial communities within the three soil samples collected adjacent to the middle quadrat and one soil sample adjacent to the lower and upper quadrats were characterized by using sequence analysis of clone libraries (five total)
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Only informative base positions were used to bin sequences into phylotypes and build the microbial phylogenetic tree. All diversity analyses were later repeated by using 97%, 94%, and 90% sequence similarity cutoffs (Figs.
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From page 144... ...
, we measured the extent to which co-occurring species in a community are phylogenetically related compared with what is expected by chance. With both indices, the phylogenetic structure of the observed community was compared to a null expectation obtained by randomly sampling the pool of all of the species identified in the study 1,000 times, while constraining both the number of taxa in the community and species occurrence across
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From page 145... ...
Using PhyloSor, one can test whether two communities are phylogenetically more or less similar than what is expected given their taxa similarity. This is done by comparing the phylogenetic similarity of the observed communities to a null expectation obtained by randomly sampling the pool of all of the species identified in the study while constraining the number of taxa in each community and the number of taxa shared by the two communities.
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From page 146... ...
The significance of results did not differ between repeated subsamples. Linking Diversity Measurements to Environmental Parameters To determine the correlation between elevation and potential environmental drivers with the observed diversity patterns, we used polynomial regression analysis.
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From page 147... ...
Logistical support was provided by National Science Foundation Grant DBI 0420919 (to Ian Billick)
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