Ephemeral rain pools contain diverse assemblages of protists and small
metazoans. Rain pool organisms survive periods of desiccation as dorm
ant cysts or resting stages, and become active shortly after the pools
fill with water. Non-equilibrium mechanisms related to the frequent d
rying of pools could promote the observed coexistence of over 15 speci
es of ecologically similar microorganisms. We used dormant organisms f
rom the substrate of a well-characterized ephemeral pool to create 20
microcosms that experienced two different disturbance regimes. Undistu
rbed microcosms held a constant volume of medium over the entire 30-d
study period. Disturbed microcosms dried periodically, at approximatel
y five-d intervals, and were then refilled with medium to initiate new
rounds of community development. Daily monitoring of the presence or
absence of active organisms provided information about the number and
identity of species in disturbed and undisturbed microcosms. Undisturb
ed microcosms contained a greater number of active species, primarily
because some predatory species only became active after at least five
to ten d of uninterrupted community development. Species composition d
iverged rapidly after the first drying episode as communities in undis
turbed and disturbed microcosms developed along different successional
trajectories. If non-equilibrium mechanisms contribute to diversity i
n this system, their contribution must occur over more episodes of dis
turbance than we observed.