Abstract
Considerable emphasis has been placed recently on the importance of incorporating non‐trophic effects into our understanding of ecological networks. Interaction modifications are well‐established as generating strong non‐trophic impacts by modulating the strength of interspecific interactions.For simplicity and comparison with direct interactions within a network context, the consequences of interaction modifications have often been described as direct pairwise interactions. The consequences of this assumption have not been examined in non‐equilibrium settings where unexpected consequences of interaction modifications are most likely.To test the distinct dynamic nature of these “higher‐order” effects, we directly compare, using dynamic simulations, the robustness to extinctions under perturbation of systems where interaction modifications are either explicitly modelled or represented by corresponding equivalent pairwise non‐trophic interactions.Full, multi‐species representations of interaction modifications resulted in a greater robustness to extinctions compared to equivalent pairwise effects. Explanations for this increased stability despite apparent greater dynamic complexity can be found in additional routes for dynamic feedbacks. Furthermore, interaction modifications changed the relative vulnerability of species to extinction from those trophically connected close to the perturbed species towards those receiving a large number of modifications.Future empirical and theoretical research into non‐trophic effects should distinguish interaction modifications from direct pairwise effects in order to maximize information about the system dynamics. Interaction modifications have the potential to shift expectations of species vulnerability based exclusively on trophic networks.
Highlights
There is a building appreciation that to improve our understanding of population dynamics within ecological communities, it is necessary to move beyond studies that focus on a single interaction process at a time (Kéfi et al, 2012; Levine, Bascompte, Adler, & Allesina, 2017)
Interaction modifications are potent forces that introduce distinct dynamics to ecological networks. This distinctive nature of interaction modifications is of relevance for dynamic systems in many fields that make use of networks (Strogatz, 2001) since our
Despite long‐standing calls for the inclusion of non‐ trophic effects (NTEs) into the mainstream of ecological network science that has been long dominated by food webs (Ings et al, 2009), and the publication of the first empirical community level non‐trophic network (Kéfi et al, 2015), there remains a great number of significant unknowns about the role of NTEs at the network scale
Summary
There is a building appreciation that to improve our understanding of population dynamics within ecological communities, it is necessary to move beyond studies that focus on a single interaction process at a time (Kéfi et al, 2012; Levine, Bascompte, Adler, & Allesina, 2017). It has been empirically demonstrated that many strong non‐ trophic effects (NTEs) are caused by such processes, with large implications for community structure and dynamics (Ohgushi, Schmitz, & Holt, 2012; Preisser, Bolnick, & Benard, 2005; Werner & Peacor, 2003). It has been repeatedly shown that interaction modifications can cause qualitatively distinct responses to perturbations than may otherwise be expected (Barbosa, Fernandes, Lewis, & Morris, 2017; Donohue et al, 2017; Matassa, Ewanchuk, & Trussell, 2018; van Veen, van Holland, & Godfray, 2005)
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