Evolution of resource use along a gradient of stress leads to increased facilitation

Abstract

The stress‐gradient hypothesis (SGH) posits that the relative importance of facilitative interactions versus negative interactions increases as levels of abiotic stress increase. Originally formulated in empirical studies of plant populations, in recent years the SGH has been found to describe how interactions change in response to stress in a wide range of species including algae, mussels and moths. However, there has been little theory attempting to predict patterns from first principles in relation to different types of interactions. Here, we use mathematical models of microbial populations to investigate whether patterns consistent with the SGH arise when species interact through resource use and allelopathy. Evolution alters the degree to which competition for resource use versus facilitation (cross‐feeding) occurs. Our results are consistent with the SGH; species interactions evolve to be more facilitative as average stress intensifies. This occurs because at greater stress the species evolve to become specialists on either of the two resources thereby decreasing overlap in resource use and increasing facilitation through cross‐feeding. In addition, the production of toxic allelopathic compounds decreases as stress intensifies due to density‐dependent effects. Our results suggest that the SGH could arise through fundamental interactions that are common to many organisms and therefore that the SGH could be a more widespread phenomenon than previously recognised.

The key to complexity in interacting systems with multiple strains

“…The SGH predicts that positive interactions should be more prevalent in stressful environments, while more favourable environments should favour competition. This hypothesis has been supported and tested mainly in plant systems (Callaway et al, 2002;Eränen and Kozlov, 2008;Pugnaire and Luque, 2001), and more recently in microbial communities (Fetzer et al, 2015;Hoek et al, 2016;Lawrence and Barraclough, 2016;McCluney et al, 2012;Piccardi et al, 2019).…”

Integrating demography, dispersal and interspecific interactions into bird distribution models

“…As the residual correlations estimated by JSDMs simply indicate whether co‐occurrence is lower or higher than expected by chance given the environment, we can assume that current JSDM implementations will not allow unambiguous distinction of predator–prey (or consumer–resource) relationships and competitive or facilitative interactions, and will need further model development in this respect. Another challenge is that interspecific interactions are not constant in space and time (Callaway et al , Meier et al , He et al , Lawrence and Barraclough ), and it has thus been proposed that non‐stationarity in interaction coefficients should be considered in future research (Kissling et al , Wisz et al , Warton et al ) but hitherto only one worked example using multi‐species occupancy modelling exists (Rota et al ).…”

Predator coevolution and prey trait variability determine species coexistence

“…competitive exclusion is facilitated by evolutionary change in between-species interactions [13,[26][27][28], resulting in, crossfeeding [26] or a niche shift to underexploited resources [29 -31]. In most bacterial experiments, monoclonal isolates are assembled [13,21,23,26,32] and any evolutionary change is based on de novo mutations [33 -35], potentially imposing constraints on evolution [4].…”