Data from: Disturbance-mediated consumer assemblages determine fish community structure and moderate top-down influences through bottom-up constraints

Disturbance is a strong structuring force that can influence the strength
of species interactions at all trophic levels, but controls on the
contributions to community structure of top-down and bottom-up processes
across such gradients remain poorly understood. Changes in the composition
of predator and consumer assemblages, and their associated traits, across
gradients of environmental harshness (e.g., flooding) are likely to be a
particularly important influence on the strength of top-down control and
may drive bottom-up constraints. We examined how consumers with particular
traits, and the predators that consumed them, varied across a gradient of
stream flooding disturbance and used experiments to assess the predation
impact on those contrasting consumer communities (ultimately quantifying
how flood disturbance altered the strength of top-down control). Consumer
community composition and mobility were strongly related to flood
disturbance; the biomass and drift of protected primary consumers (i.e.,
those with morphological defences) decreased with increasing flood
disturbance. Predatory fish species had different disturbance niches, and
path analysis identified that both direct flood-disturbance effects and
indirect bottom-up constraints of flood-disturbance on consumers
influenced predatory fish composition and biomass. Fishes generally fed
most effectively on consumer types associated with their particular niche,
but all fishes were strongly size-selective when feeding on protected
consumers. Although protected consumers did not grow large enough to
escape predation, an in situ experiment showed protected consumers were at
a reduced risk of predation as disturbance increased compared to
unprotected consumers. Overall, top-down control declined with flood
disturbance, but the effect depended on consumer traits. Predatory fishes
were only capable of exerting top-down control on protected consumers in
benign habitats but impacted unprotected consumers across a larger range
of the disturbance gradient. Collectively our findings suggest that a
shift towards a more disturbed state will probably result in reduced
predator impacts and a weakening of top-down control. Moreover, predicted
increases in the frequency and intensity of climatic events causing
disturbance, such as flooding, are likely to result in a community shift
that disproportionately impacts protected consumers and the predators that
utilise them as prey through the subsequent bottom-up constraints.