Transient invaders can induce shifts between stable states of microbial communities

Microbial dispersal often leads to the arrival of outsider organisms into
ecosystems. When their arrival give rise to successful invasions, outsider
species establish within the resident community, which can dramatically
alter the ecosystem. Seemingly less influential, the potential impact of
unsuccessful invaders that interact only transiently with the community
has remained largely ignored. Here, we experimentally demonstrate that
such transient invasions can perturb the stability of microbial ecosystems
and induce a lasting transition to an alternative stable state, even when
the invader species itself does not survive the transition. First, we
develop a mechanistic understanding of how environmental changes caused by
such transient invaders can drive a community shift in a simple, bistable
model system. Beyond this, we show that transient invaders can also induce
switches between stable states in more complex communities isolated from
natural soil samples. Our results demonstrate that short-term interactions
with an invader species can induce lasting shifts in community composition
and function.