Mutualisms in a warming world: How increased temperatures affect the outcomes of multi‐mutualist interactions

Abstract

In nature, plant species simultaneously interact with many different mutualistic partners. These mutualists may influence one another through direct interference or indirectly by competing for shared reward resources or through alteration of plant traits. Together, these mutualists also may combine to affect plant hosts in ways that may not be predictable based on pairwise interactions. Given that the outcome of mutualistic interactions often depends on environmental conditions, multi‐mutualist effects on one another, and their plant hosts may be affected by global changes. Here, we grew focal plants under simulated global warming conditions and manipulated the presence of partner mutualists to test how warming affects the outcome of interactions between focal plants and their partners (nitrogen‐fixing rhizobia, ant defenders, and pollinators) and interactions among these partner mutualists. We find that warming alters the fitness benefits plants receive from rhizobium resource mutualists but not ant mutualists and that warming altered plant investment in all mutualists. We also find that mutualist partners interact, often by altering the availability of plant‐produced rewards that facilitate interactions with other partners. Our work illustrates that global changes may affect some but not all mutualisms, often asymmetrically (e.g., affecting investment in the mutualist partner but not plant host benefits) and also highlights the ubiquity of interactions between the multiple mutualists associating with a shared host.

Mutualisms in a warming world

“…While beyond the scope of the discussion here, we acknowledge that trait trade‐offs might exist among non‐mutualistic traits that can influence a species' resource investment into mutualism (e.g. see Magnoli et al, 2023). Lastly, we provide a summary illustration of how the TEM framework is complementary to the Y model (Figure 4d).…”

“…An important future direction for the TEM framework then might be considering MTPCs and MTPAs beyond mutualisms. These metrics can be extended by placing mutualism within a larger community context (Afkhami et al, 2020; Afkhami et al, 2021; Dunkley et al, 2020; Kordas et al, 2011; Magnoli et al, 2023). To that end, it may prove fruitful to expand our geometric interpretation of performance curves and performance areas to include performance volumes (e.g.…”