COS 287-5 - Resistance and resilience of microbial communities to invasion: The role of community synchrony, competition, and environmental variability

Abstract: Synchrony is a widespread phenomenon found in many ecological communities, where species’ abundances may fluctuate in a positively correlated (synchronous) or negatively correlated (compensatory) manner across time, due to underlying drivers such as environmental fluctuations and interspecific competition. Previous theoretical simulations of ecological communities have shown that compensatory communities are more likely to be sensitive to invasion, but it remains unknown if these findings extend to empirical, non-simulated systems. Therefore, the objective of this research was to determine 1. How two-species communities react to environmental variation, and subsequently how these interactions impact the community’s degree of synchrony, and 2. How they respond to the introduction of an invader. We used ciliated protist species to create multiple replications of two-species resident communities, allowing them to establish for several days, before introducing the third species as the novel invader. We elucidated temporal synchrony dynamics by varying the environmental effect of light availability, and then tested the communities’ resistance and resilience by introducing the invader during different phases of synchrony. Through this, we were able to compare invader growth and suppression in microcosm communities across different dynamics. Across two treatments of constant and varying light availability, resident microcosms experienced either synchronous dynamics, with an average variance ratio of 1.19, or compensatory dynamics, with an average variance ratio of 0.82. To test community resistance, the invading protist was introduced with a stepwise process and resulted in differential invasion success between communities in different environmental conditions. In the varying light treatment, during periods when light availability decreased, the invader grew to higher abundances (N_initial = 20, N_final = 57.2±8.35) than during periods of increased light availability (N_initial = 20, N_final = 35.75±8.35). Microcosms where the invader grew more quickly had compensatory dynamics prior to their invasion. In testing long-term resilience, the introduction of the invader decreased synchrony of communities in both environmental treatments. Both resistance and resilience experimental tests parallel results of simulated models, indicating that compensatory communities can be more sensitive to invasion. Testing model predictions with empirical experiments elucidate which aspects of our theoretical model hold in a live system and which aspects need refining for the ultimate goal of predicting which communities are most vulnerable to invasion in natural systems.