DDR Experiments 2013

Diversity 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 types,
which gave rise to transient diversity maxima when community types 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.