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

Invasions are commonly found to benefit from disturbance events. However, the importance of the relative timing of the invasion and disturbance for invader success and impact on community composition remains uncertain. Here, we experimentally test this by invading a five-species bacterial community on eight separate occasions—four before a disturbance and four after. Invader success and impact on community composition was greatest when the invasion immediately followed the disturbance. However, the subsequent invasions had negligible success or impact. Pre-disturbance, invader success and impact was greatest when the invader was added just before the disturbance. Importantly, however, the first three pre-disturbance invasion events had significantly greater success than the last three post-disturbance invasions. Moreover, these findings were consistent across a range of propagule pressures. Overall, we demonstrate that timing is highly important for both the success and impact on community composition of an invader, with both being lower as time since disturbance progresses.