Disturbance Regimes Predictably Alter Diversity in an Ecologically Complex Bacterial System.

Sean M Gibbons,Monika Scholz,Maureen L Coleman,Alan L Hutchison,Jack A Gilbert,Aaron R Dinner,Mary Ann Moran

doi:10.1128/mbio.01372-16

Abstract

ABSTRACTDiversity is often associated with the functional stability of ecological communities from microbes to macroorganisms. Understanding how diversity responds to environmental perturbations and the consequences of this relationship for ecosystem function are thus central challenges in microbial ecology. Unimodal diversity-disturbance relationships, in which maximum diversity occurs at intermediate levels of disturbance, have been predicted for ecosystems where life history tradeoffs separate organisms along a disturbance gradient. However, empirical support for such peaked relationships in macrosystems is mixed, and few studies have explored these relationships in microbial systems. Here we use complex microbial microcosm communities to systematically determine diversity-disturbance relationships over a range of disturbance regimes. We observed a reproducible switch between community states, which gave rise to transient diversity maxima when community states were forced to mix. Communities showed reduced compositional stability when diversity was highest. To further explore these dynamics, we formulated a simple model that reveals specific regimes under which diversity maxima are stable. Together, our results show how both unimodal and non-unimodal diversity-disturbance relationships can be observed as a system switches between two distinct microbial community states; this process likely occurs across a wide range of spatially and temporally heterogeneous microbial ecosystems.

Highlights

Diversity is often associated with the functional stability of ecological communities from microbes to macroorganisms
The intermediate disturbance hypothesis (IDH) postulates that these peaks in diversity at intermediate levels of disturbance stem from the coexistence of organisms with different life history traits, such as those defined by competition-colonization tradeoffs, along a successional gradient [21, 22, 27, 28]
Throughout the course of the experiment, a single cyanobacterial operational taxonomic unit (OTU) closely related to Synechococcus elongatus comprised ~80% of sequence reads in the undisturbed controls, and the remaining ~20% of reads represented a diverse, heterotroph community dominated by Proteobacteria (Fig. 1; see Text S1 in the supplemental material)

Summary

Introduction

Diversity is often associated with the functional stability of ecological communities from microbes to macroorganisms. Our results show how both unimodal and non-unimodal diversity-disturbance relationships can be observed as a system switches between two distinct microbial community states; this process likely occurs across a wide range of spatially and temporally heterogeneous microbial ecosystems. Similar to what has been found in large-scale ecosystems [3], diversity in microbial systems is often linked to ecological function and stability. In order to predict how disturbance might impact ecosystem function, it is important to determine whether there are general rules governing the relationship between microbial community diversity and environmental change. Recent laboratory work has shown that multispecies microbial community responses to disturbance depend on intensity and on the frequency of disturbance application [34, 36], suggesting that a simple universal relationship between diversity and disturbance may not exist. Together our experimental and modeling results suggest conditions under which a variety of unimodal and non-unimodal DDRs can be observed, in microbial systems, but potentially in macroscale ecosystems as well

Methods

Results

Conclusion