On the sensitivity of food webs to multiple stressors

Abstract

Evaluating the effects of multiple stressors on ecosystems is becoming increasingly vital with global changes. The role of species interactions in propagating the effects of stressors, although widely acknowledged, has yet to be formally explored. Here, we conceptualise how stressors propagate through food webs and explore how they affect simulated three‐species motifs and food webs of the Canadian St. Lawrence System. We find that overlooking species interactions invariably underestimate the effects of stressors, and that synergistic and antagonistic effects through food webs are prevalent. We also find that interaction type influences a species’ susceptibility to stressors; species in omnivory and tri‐trophic food chain interactions in particular are sensitive and prone to synergistic and antagonistic effects. Finally, we find that apex predators were negatively affected and mesopredators benefited from the effects of stressors due to their trophic position in the St. Lawrence System, but that species sensitivity is dependent on food web structure. In conceptualising the effects of multiple stressors on food webs, we bring theory closer to practice and show that considering the intricacies of ecological communities is key to assess the net effects of stressors on species.

Interactive effects of multiple stressors vary with consumer interactions, stressor dynamics and magnitude

“…Our inclusion of a consumer-resource model supports recent calls for research examining interactions at higher levels of biological organisation (Orr et al, 2020), supporting previous work demonstrating that species interactions can change stressor interaction types (Beauchesne et al, 2021;Thompson et al, 2018). Indeed, species interactions can amplify or dampen the sensitivity of natural systems to stressors.…”

Predators mitigate the destabilising effects of heatwaves on multitrophic stream communities

“…For example, Kordas et al (2017) found that a key mechanism driving this pattern in rocky intertidal communities was the action of herbivores modifying the spatial variability of algal community structure. Our findings suggest predator effects on spatial variability occur indirectly through their effects on macroinvertebrate herbivores, highlighting the importance of both direct and indirect ecological interactions in providing resistance against heatwaves and climate warming more generally (Goldenberg et al, 2018;Kordas et al, 2017;Zarnetske et al, 2012; see also Beauchesne et al, 2021).…”

Ranking species based on sensitivity to perturbations under non-equilibrium community dynamics

“…In order to avoid the loss of biodiversity and ecosystem services under these circumstances, it is crucial to understand not only the response of the whole community to perturbations, but also the response of its constituent species. Individual species may vary in their sensitivity to perturbations—that is, how much their abundance change after a perturbation—and such sensitivity may be linked to their role in the community (Beauchesne et al ., 2021, Dirzo et al ., 2014, Estes et al ., 2011). For instance, keystone species such as apex predators can be highly sensitive to perturbations and also crucial to maintain community functioning (Estes et al ., 2011).…”

“…Following these theoretical developments, indicators such as species abundance or rate of decline are routinely used to characterize the behavior of populations and determine extinction risks, serving as crucial management and conservation tools (Mace et al ., 2008). More recently, several studies have incorporated information on species interactions to further explore how individual species respond to perturbations (Arnoldi et al ., 2018, Beauchesne et al ., 2021, Ives et al ., 1999, Medeiros et al ., 2021, Saavedra et al ., 2011, Weinans et al ., 2019) and, in turn, how individual species can inform us about whole-community changes (i.e., best-indicator or sensor species) (Aparicio et al ., 2021, Dakos, 2018, Ghadami et al ., 2020, Lever et al ., 2020, Patterson et al ., 2021). These studies often rely on the assumption of a population dynamics model under a stable equilibrium to which the community returns after a small perturbation on abundances.…”