Mutualisms in a warming world

Abstract

Predicting the impacts of global warming on mutualisms poses a significant challenge given the functional and life history differences that usually exist among interacting species. However, this is a critical endeavour since virtually all species on Earth depend on other species for survival and/or reproduction. The field of thermal ecology can provide physiological and mechanistic insights, as well as quantitative tools, for addressing this challenge. Here, we develop a conceptual and quantitative framework that connects thermal physiology to species' traits, species' traits to interacting mutualists' traits and interacting traits to the mutualism. We first identify the functioning of reciprocal mutualism‐relevant traits in diverse systems as the key temperature‐dependent mechanisms driving the interaction. We then develop metrics that measure the thermal performance of interacting mutualists' traits and that approximate the thermal performance of the mutualism itself. This integrated approach allows us to additionally examine how warming might interact with resource/nutrient availability and affect mutualistic species' associations across space and time. We offer this framework as a synthesis of convergent and critical issues in mutualism science in a changing world, and as a baseline to which other ecological complexities and scales might be added.

A framework for understanding climate change impacts through non‐compensatory intra‐ and interspecific climate change responses

“…There are many ways in which differing responses of mutualistic partners to climate change can lead to non-compensatory uptake rate effects, phenological mismatches, or other non-compensatory effects that alter the connecting rate with potential cascading effects for either or both mutualistic partners. In a recent review, Cruz et al (2023) highlighted how differing thermal performance curves of mutualistic partners in traits related to the interaction among partners can generate an overall mutualism thermal performance curve, making the mutualism itself temperature dependent.…”

“…In a recent review, Cruz et al. (2023) highlighted how differing thermal performance curves of mutualistic partners in traits related to the interaction among partners can generate an overall mutualism thermal performance curve, making the mutualism itself temperature dependent. Given that mutualistic interactions generally involve connections to rates such as uptake rates and extrinsic death rates, the temperature dependence of mutualisms generated by non‐compensatory effects can potentially lead to changes that could scale up to a non‐compensatory demographic effect and population growth or decline.…”

“…In this case, changes in the relative potential benefits of bacterivory and photosynthates from the algae with temperature generate a non‐compensatory effect on uptake rates that switches the presence of algae from beneficial to detrimental. Given the potential for the costs and benefits or symbioses to be environmentally dependent (Bronstein, 1994; Cruz et al., 2023; Hoeksema & Bruna, 2015; Johnson et al., 1997), non‐compensatory climate change effects may play a particularly important role in moving host‐symbiont relationships along the mutualism–parasitism continuum.…”

A framework for understanding climate change impacts through intra- and interspecific asymmetries in climate change responses

“…There are many ways in which differing responses of mutualistic partners to climate change can lead to uptake rate asymmetries, phenological mismatches, or other asymmetries that alter the mutualism connecting rate with potential cascading effects for either or both partners. In a recent review, Cruz et al (2023) highlighted how differing thermal performance curves of mutualistic partners in traits related to the interaction among partners can generate an overall mutualism thermal performance curve, making the mutualism itself temperature dependent. Given that mutualistic interactions generally involve connections to rates such as uptake rates and extrinsic death rates, the temperature dependence of mutualisms generated by asymmetric responses can potentially lead to changes that could scale up to a demographic asymmetry and population growth or decline.…”

“…In this case, changes in the relative potential benefits of bacterivory and photosynthates from the algae with temperature generate an asymmetric effect on uptake rates that switches the presence of algae from beneficial to detrimental. Given the potential for the costs and benefits or symbioses to be environmentally dependent (Bronstein 1994;Cruz et al 2023;Hoeksema & Bruna 2015;Johnson et al 1997), asymmetric climate change effects may play a particularly important role in moving hostsymbiont relationships along the mutualism-parasitism continuum.…”