Resistance and resilience to invasion is stronger in synchronous than compensatory communities
Wednesday, August 4, 2021
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Janette Davidson, Department of Botany, University of Wyoming, Laramie, WY and Lauren G. Shoemaker, Botany Department, University of Wyoming, Laramie, WY
Presenting Author(s)
Janette Davidson
Department of Botany, University of Wyoming Laramie, WY, USA
Background/Question/Methods Synchrony is a widespread phenomenon found in many ecological communities, where species’ abundances fluctuate in a positively correlated (synchronous) or negatively correlated (compensatory) manner across time due to underlying drivers such as environmental fluctuations and interspecific competition. However studies of synchrony, and especially theoretical understandings of its mechanisms, are rarely integrated with invasion ecology. Therefore, the objective of this research was to determine if the levels of synchrony in a community, and its underlying drivers, alter a community’s resistance and resilience to invasion. We test this with an integration of a theoretical approach, by developing a Lotka-Volterra competition model that we adapt from Loreau and de Mazencourt (2013), as well as with empirical studies, by simulating invasive events in protist microcosms. In both the model and microcosms, we created resident two-species communities operating under varying environmental and competitive strength, which elicited synchrony dynamics. We then tested the communities’ resistance and resilience by simulating or introducing the invasion of a third exotic species at different timesteps. Additionally, we simulated different invader parameters in the model, to test underlying effects of invader demography. The model projects community patterns after successful invasions, the results of which are tested against the microcosm data. Results/Conclusions Across 2,000 replicates of 500 timesteps each, our model yielded variance ratios ranging from 0 (compensatory) to 2 (highly synchronous) across parameter combinations. As species’ responses to environmental fluctuations increase, synchrony increases; conversely, as the degree of competition increases, so does compensation. Furthermore, we determined that synchronous communities were able to resist invasion 18.25% - 89.25% of the time, depending on the invader’s demographic rates. Compensatory communities were occasionally more resistant to invaders with low intrinsic growth rates, but were extremely vulnerable to good invaders, where they were never able to resist. Extending to resiliency, synchronous communities were better able to suppress growth of invaders, and were the only communities able to drive both good and bad invaders to extinction. Synchrony dynamics have been observed in protist microcosms after subjugation to environmental fluctuations and different competitive interactions between species, with variance ratios ranging between 0.9 to 1.22, and preliminary results show that synchronous communities had slightly higher invader growth rates. These results highlight that communities can be both resilient or susceptible to invasions at different points in time depending on demographic and environmental factors, and yields key insights into which communities are most at-risk for the establishment of novel species.