Disturbances can facilitate prior invasions more than subsequent invasions in microbial communities

Abstract

Invasions by microorganisms are commonly found to benefit from disturbance events. However, the importance of the relative timing and order of the invasion and disturbance for invader success remains uncertain. Here, by invading a stably coexisting community of five bacterial species at four different propagule pressures on eight separate occasions - four pre-disturbance and four post-disturbance - we experimentally tested the importance of timing and order for the invaders success. Furthermore, we quantified the impact of the invader on the composition of the resident community. Across a range of invader densities, both pre- and post-disturbance invader success was greatest the closer in time to the disturbance. While the greatest invasion success occurred when the invasion immediately followed the disturbance, invasion resistance rapidly recovered, such that the three subsequent invasions had negligible success. As a consequence, overall invader success was greatest pre-than post-disturbance. We found that invasion day as well as success significantly affected resident diversity, such that it was lowest in communities invaded immediately after the disturbance, but was overall lower in communities invaded pre-disturbance. Overall, these results demonstrate that invading immediately after a disturbance is highly beneficial for invader success and results in the biggest change to community composition. Importantly however, they also show that this window of opportunity is very brief, and that, on average, an invader will have a greater success and effect on community composition if it invades before a disturbance.