Species often interact with multiple mutualistic partners that provide functionally different benefits and/or that interact with different life-history stages. These functionally different partners, however, may also interact directly with one another in other ways, indirectly altering net outcomes and persistence of the mutualistic system as a whole. We present a population dynamical model of a three-species system involving antagonism between species sharing a mutualist partner species with two explicit life stages. We find that, regardless of whether the antagonism is predatory or non-consumptive, persistence of the shared mutualist is possible only under a restrictive set of conditions. As the rate of antagonism between the species sharing the mutualist increases, indirect rather than direct interactions increasingly determine species’ densities and sometimes result in complex, oscillatory dynamics for all species. Surprisingly, persistence of the mutualistic system is particularly dependent upon the degree to which each of the two mutualistic interactions is specialized. Our work investigates a novel mechanism by which changing ecological conditions can lead to extinction of mutualist partners and provides testable predictions regarding the interactive roles of mutualism and antagonism in net outcomes for species’ densities.

物种经常与提供功能上不同利益和/或与不同生活史阶段相互作用的多个互惠伙伴互动。但是，这些功能不同的合作伙伴也可以其他方式直接彼此交互，从而间接改变净结果和整个互惠体系的持久性。我们提出了一个三物种系统的种群动力学模型，该系统涉及具有两个明确生命阶段的互惠伙伴物种之间的对抗。我们发现，无论对抗是掠夺性的还是非消费性的，只有在一套限制性条件下，共同互助主义者的坚持才有可能。随着共享共生主义的物种之间的对抗速度增加，间接而不是直接的相互作用越来越多地决定物种的密度，有时会导致所有物种复杂的振荡动态。出乎意料的是，互惠系统的持久性尤其取决于两个互惠互动中每一个的专业化程度。我们的工作探讨了一种新颖的机制，通过这种机制，生态条件的变化会导致互惠伴侣的灭绝，并就物种密度的净结果中的互惠和拮抗作用相互作用提供可验证的预测。