A dynamic model of facilitation on environmental stress gradients

Abstract

Theories based on competition for resources in animals and other non‐sessile organisms rarely consider the role of facilitative interactions. Yet these interactions are important for community assembly, especially under stressful environments (e.g. the stress‐gradient hypothesis, SGH). To make an explicit link between species interaction theory and SGH patterns, I used a classic resource competition model promoting coexistence between a beneficiary and its facilitator sharing a common resource along a stress gradient. I compared model outcomes for two fundamentally different mechanisms of facilitation (alleviation of resource versus non‐resource stress), and also tested the effect of a reciprocal cost of facilitation from the beneficiary. I then tested model's biological relevance using experimental data from two tuber moth species (Lepidoptera, Gelechiidae) for which facilitation in resource access was previously established. Simulation outcomes revealed that both the mode of facilitation and the incorporation of facilitation costs affected the shape of the facilitation–stress relationship. These predictions are in line with current SGH observations and experiments on both plants and animals and reconcile the frequently reported variability of this relationship in nature. Moreover, a sensitivity analysis of model's parameters confirmed the robustness of the modelling framework to uncover the mechanisms responsible for observed species interaction–stress patterns. Finally, when parameterized with tuber moth demographic data, model's results corresponded to observed interaction outcomes along resource stress gradients. Overall, having a common model for plants and animals may simplify assumptions in SGH studies, allow contrasting the shapes of different consumer–resource relationships and specifying the conditions that favour one type of interaction outcome over another.

Indirect facilitation drives species composition and stability in drylands

“…different c values for each species), according to the competition/defence trade off (Bazzaz et al, 1987;Viola et al, 2010). Then, the cost would be density dependent as in the study of Dangles (2019). Our results on facilitation cost indicates that a better understanding of the effects of facilitation on the benefactor necessitates to scale up studies from the individual plant to the community and ecosystem level.…”

“…Indirect facilitation through grazing increases the density of the protegee until it reaches a sufficient density to progressively exclude the nurse. The question of the nurse cost is relatively new in plant facilitation research (Schöb et al, 2014;García et al, 2016;Dangles, 2019). Previous studies showed that a beneficiary species can have a negative effect on the reproductive output of its benefactor (Schöb et al, 2014;García et al, 2016).…”

Mixed-species bird flocks re-assemble interspecific associations across an elevational gradient

“…Understanding how communities respond to environmental change is one of the essential aims of ecology [1,2]. Three non-exclusive mechanisms can summarize these responses, including the alteration of community assemblages (i.e.…”

Modeling the continua in the outcomes of biotic interactions

“…In interspecific interactions resources are entire individuals or part of them that are exploited by the interacting partners. C‐R models have proven very useful to describe the behavior of many different types of interactions, such as predator–prey interactions (Turchin, 2003), plant‐herbivore interactions (Feng & DeAngelis, 2018), host–parasite interactions (Roberts, 1995), mutualistic interactions (Holland & DeAngelis, 2009, 2010) and facilitation‐competition interactions (Dangles, 2019).…”