Mathematical insights into mechanisms leading to coexistence and competitive exclusion among mutualist guilds

In the last decades, microbial inoculants have been used as organic fertilizers worldwide. One of the most widely used commercial products are arbuscular mycorrhizal (AM) fungi, as these fungi can associate with a vast variety of crops cultivated in agriculture. Despite the potential benefits for soil quality and crop yield associated with the use of AM fungi, experiments assessing the effective establishment of the fungi in the field have given inconsistent results. Additionally, it is not yet clear whether the introduction of commercial inoculants could lead to a biodiversity loss in the native fungal community, and ultimately have a negative impact on plant growth. Here I develop a series of ordinary and partial differential equation models to discuss the establishment and regional spread of the inoculants in the field from a theoretical point of view. I use linear and nonlinear stability analysis and extensive numerical simulations to study the spatio-temporal dynamics of a guild of mutualists (the fungal species) sharing a resource provided by the same partner (the host plant), constituting a shared resource for all fungi. My results shed light on the discordant experimental observations found in the literature, and allow to assess the risks and benefit of inoculation. I identify under which conditions inoculation can effectively boost productivity, when it has no significant effect on plant growth and on the native fungal community, and when it represents an invasion risk. More generally, the models provide important ecological insights into the mechanisms responsible for coexistence and competitive exclusion among mutualist guilds, and constitute a framework to predict the consequences of species manipulation in mutualist communities. Indeed, the models I have developed are simple enough to apply to a broad range of mutualisms found in nature, such as pollination or seed dispersal.Arts and Sciences, Irving K. Barber School of (Okanagan)Computer Science, Mathematics, Physics and Statistics, Department of (Okanagan)Graduat