Disturbances can facilitate biological invasions, with the associated increase in resource availability being a proposed cause. Here, we experimentally test the effects of disturbance regime and resource abundance on invasion success. We invaded populations of the bacterium Pseudomonas fluorescens with two invader morphotypes in a factorial design containing five disturbance frequencies and three resource levels. As resident populations were altered by the treatments, we additionally tested their effect on invader success. Disturbance frequency and resource abundance interacted to affect the success of both invaders. For one, success was positively affected by disturbance under high resources but negatively under low. For the other, disturbance negatively affected success under high resource abundance but not under low or medium. Resident population changes did not alter invader success beyond direct treatment effects. Overall, how disturbance affects invasion success is dependent on community resource abundance, and this interaction acts differently on invaders with different life-histories.

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.