When cheating turns into a stabilizing mechanism of mutualistic networks

Abstract

Mutualistic interactions, such as plant-mycorrhizal or plant-pollinator interactions, are widespread in ecological communities and frequently exploited by cheaters, species that benefit from interactions without providing commodities in return. Cheating is often thought to negatively affect the fitness of the cheated individuals, but its effect at community level remains poorly studied. Here, we describe two different kinds of cheating in mutualistic networks and show that they have very different consequences for the ecological stability of the community. Conservative cheating is when a species cheat on their mutualistic partners to escape the cost of mutualistic interactions. In contrast, innovative cheating occurs when a species cheats with partners that it would otherwise not have access to. Using a theoretical model, we found that network persistence is negatively affected by conservative cheating but can be enhanced by innovative cheating. Innovative cheating becomes a stabilizing mechanism when cheaters have few mutualistic partners, cheat at low or intermediate frequency and when the cost associated with mutualism is not too high. In this case, the negative effects of cheating on partner persistence are overcompensated at the community level by the positive feedback loops arising in mutualistic networks. Using an empirical dataset of plant-bird interactions, we found that observed cheating patterns are highly consistent with theoretical cheating patterns that increase network persistence. This result suggests that eco-evolutionary dynamics tend to produce cheating patterns that increase the ecological stability of communities. Thus, cheating observed in nature could contribute to stabilize mutualistic communities instead of destabilizing them.

A probabilistic view of forbidden links: their prevalence and their consequences for the robustness of mutualistic networks

“…It is important to note that we studied forbidden links in terms of mutualistic interactions because we excluded cheating interactions in which hummingbirds pierce the corolla or use an existing hole to rob the nectar. These interactions can allow species to have access to unavailable partners (Duchenne et al 2023;Rojas-Nossa et al 2016), and thus blur the limit between forbidden and possible interactions. However, these interactions are likely to be antagonistic rather than mutualistic because plants pay the cost of nectar production but do not get pollinated, suggesting that these interactions remain forbidden for mutualism.…”

Integrating ecological feedbacks across scales and levels of organization

“…Such changes of the emergent biotic feedbacks ultimately affect the stability of communities (e.g., Kondoh 2012, Coyte et al 2015). Duchenne et al (2023) recently suggested that when cheaters emerge among pollinators, they reduce the community-level positive feedback between mutualistic species, which can negatively impacts community persistence.…”