Abstract
Anthropogenic activities expose many ecosystems to multiple novel
disturbances simultaneously. Despite this, how biodiversity responds to
simultaneous disturbances remains unclear, with conflicting empirical
results on their interactive effects. Here, we experimentally test how
one disturbance (an invasive species) affects the diversity of a
community over multiple levels of another disturbance regime (pulse
mortality). Specifically, we invade stably coexisting bacterial
communities under four different pulse frequencies, and compare their
final resident diversity to uninvaded communities under the same pulse
mortality regimes. Our experiment shows that the disturbances
synergistically interact, such that the invader significantly reduces
resident diversity at high pulse frequency, but not at low. This work
therefore highlights the need to study simultaneous disturbance effects
over multiple disturbance regimes as well as to carefully document
unmanipulated disturbances, and may help explain the conflicting results
seen in previous multiple-disturbance work.