Baptista JDC

Curtis TP

Davenport RJ

Pholchan MK

Sloan WT

Views of community assembly have traditionally been based on the contrastingperspectives of the deterministic niche paradigm and stochastic neutral models. Thisstudy sought to determine if we could use empirical interventions conceived from aniche and neutral perspective to change the diversity and evenness of the microbialcommunity within a reactor treating wastewater and to see if there was any associatedchange in the removal of endocrine disrupting compounds (EDCs).The systematic removalof EDCs and micropollutants from biological treatment systems is a major challengefor environmental engineers. We manipulated pairs of bioreactors in an experiment inwhich “niche” (temporal variation in resource concentration and resource complexity) and“neutral” (community size and immigration) attributes were changed and the effect on thedetectable diversity and the removal of steroidal estrogens was evaluated. The effects ofmanipulations on diversity suggested that both niche and neutral processes are importantin community assembly. We found that temporal variation in environmental conditionsincreased diversity but resource complexity did not. Larger communities had greaterdiversity but attempting to increase immigration by adding soil had the opposite effect.The effects of the manipulations on EDC removal efficiency were complex. Decreases indiversity, which were associated with a decrease in evenness, were associated with anincrease in EDC removal. A simple generalized neutral model (calibrated with parameterstypical of wastewater treatment plants) showed that decreases in diversity should leadto the increase in abundance of some ostensibly taxa rare. We conclude that neitherniche and neutral perspectives nor the effect of diversity on putative rare functionscan be properly understood by na\uefve qualitative observations. Instead, the relativeimportance of the key microbial mechanisms must be determined and, ideally, expressedmathematically

Microbial community assembly, theory and rare functions

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