Bachelot Benedicte, Lee Charlotte T
Am Nat. 2020 Mar;195(3):445-462. doi: 10.1086/707258. Epub 2020 Jan 30.
Ecosystems are under threat from anthropogenic and natural disturbances, yet little is known about how these disturbances alter mutualistic interactions. Many mutualistic interactions are highly context dependent and dynamic due to "ongoing" partner choice, impeding our understanding of how disturbances might influence mutualistic systems. Previously we showed that in the absence of additional known mechanisms of competitive coexistence, mutualistic fungi can coexist in a system where the plant community associates dynamically with two empirically defined arbuscular mycorrhizal fungal types: a cheap kind that provides low nutrient benefits, and an expensive type that provides high nutrient benefits. We built on this framework to ask how disturbances of different types, frequencies, amplitudes, and predictabilities alter ongoing partner choice and thereby influence the coexistence of mutualists. We found that the effects of disturbances depend on the type, amplitude, and predictability of disturbances and, to a lesser extent, on their frequency. Disturbance can disrupt mutualist coexistence by enabling hosts more efficiently to exclude partners that behave as parasites. Disturbance can also promote coexistence by altering the strength and direction of consumer-resource interactions. Predicting the effects of disturbance on the mutualist community therefore requires us to understand better the consumer-resource relationships under various environmental conditions. We show how, through such context-dependent effects, disturbance and ongoing partner choice can together generate relative nonlinearity and investment in future benefit, introducing fluctuation-dependent mechanisms of competitive coexistence. Our findings support a broadening of the conceptual framework regarding disturbances and competition to include fluctuation-dependent mechanisms alongside the spatiotemporal intermediate disturbance hypothesis.
生态系统正受到人为和自然干扰的威胁，但对于这些干扰如何改变互利共生相互作用，我们却知之甚少。由于存在“持续进行的”伙伴选择，许多互利共生相互作用高度依赖于环境且具有动态性，这阻碍了我们对干扰如何影响互利共生系统的理解。此前我们表明，在缺乏竞争共存的其他已知机制的情况下，互利共生真菌能够在这样一个系统中共存：植物群落与两种根据经验定义的丛枝菌根真菌类型动态关联，一种是提供低养分效益的低成本类型，另一种是提供高养分效益的高成本类型。我们在此框架基础上，研究不同类型、频率、幅度和可预测性的干扰如何改变持续进行的伙伴选择，进而影响互利共生者的共存。我们发现，干扰的影响取决于干扰的类型、幅度和可预测性，在较小程度上还取决于其频率。干扰可通过使宿主更有效地排除表现为寄生者的伙伴来破坏互利共生者的共存。干扰还可通过改变消费者 - 资源相互作用的强度和方向来促进共存。因此，预测干扰对互利共生群落的影响需要我们更好地理解各种环境条件下的消费者 - 资源关系。我们展示了干扰和持续进行的伙伴选择如何通过这种依赖于环境的效应共同产生相对非线性和对未来效益的投资，引入依赖于波动的竞争共存机制。我们的研究结果支持拓宽关于干扰和竞争的概念框架，将依赖于波动的机制与时空中间干扰假说一同纳入其中。
