plantXfungi.tex from Diversity within mutualist guilds promotes coexistence and reduces the risk of invasion from an alien mutualist

Biodiversity is an important component of healthy ecosystems, and thus understanding the mechanisms behind species coexistence is critical in ecology and conservation biology. In particular, few studies have focused on the dynamics resulting from the co-occurrence of mutualistic and competitive interactions within a group of species. Here we build a mathematical model to study the dynamics of a guild of competitors who are also engaged in mutualistic interactions with a common partner. We show that coexistence as well as competitive exclusion can occur depending on the competition strength and on strength of the mutualistic interactions, and we formulate concrete criteria for predicting invasion success of an alien mutualist based on propagule pressure, alien traits (such as its resource exchange ability) and composition of the recipient community. We find that intra guild diversity promotes the coexistence of species that would otherwise competitively exclude each other, and makes a guild less vulnerable to invasion. Our results can serve as a useful framework to predict the consequences of species manipulation in mutualistic communities.

生物多样性（Biodiversity）是健康生态系统的重要组成部分，因此阐明物种共存背后的机制在生态学与保护生物学领域至关重要。目前鲜有研究聚焦于一类物种内同时存在互利共生与竞争相互作用时所产生的动态过程。本文构建了一个数学模型，用以探究同时与同一共同伙伴存在互利共生关系的竞争类群的动态变化。研究表明，物种共存与竞争排除均可发生，具体取决于竞争强度与互利作用强度；我们还推导了具体的判定准则，可基于繁殖体压力、外来物种性状（如资源交换能力）以及接收群落的组成，预测外来互利共生物种的入侵成功率。我们发现，类群内部的多样性能够促进原本会互相竞争排除的物种实现共存，并降低整个类群遭受入侵的脆弱性。本研究结果可为预测互利共生群落中物种调控所带来的影响提供实用的理论框架。