Fig. 6. Role for environmental stress in destabilization of microbial networks.

Communities in high-stress environments (right) compared to communities in low stress environments (left) have less stable network properties. Communities under high stress are less species rich (a), less modular (b), and are less dominated by negative associations (lower negative:positive cohesion, c). The consequences for microbiomes (d) are that the reduction or loss of a taxon in response to an environmental disturbance (lightning bolt) can more easily propagate to the rest of the community (impacted taxa in black, unimpacted in gray). Positive associations (blue) are important pathways through which the effects on one taxon can cascade to impact other taxa in the community because: (1) the loss of a facilitator reduces the facilitated taxon’s fitness and/or (2) positively associated taxa are likely to be impacted by the same environmental factors (i.e., their niches strongly overlap).