Abstract
Trait-mediated indirect mutualism, or more simply synergy, between predators exploiting a joint prey occurs when the attempt by a prey to escape a predator results in a higher sensitivity to another predator. Here, we extend synergies to any case when opposed, directional selection from consumers induce rapid trait change in their joint resource. Synergies have consistently been predicted to favor species coexistence and to participate in solving the paradox of complex but stable food webs. However, synergies have rarely been empirically described.
I will present long-term evidence for a synergy between a predator (pike, Esox lucius) and a pathogen exploiting a joint prey (perch, Perca fluviatilis) in Windermere (UK). By targeting small perch, pike favored large, fast growing perch which were preferentially infected by an invading pathogen. In turn, by selecting against large, fast growing perch, the pathogen increased predation efficiency of pike on perch and decreased perch competitive ability against pike. Pathogen-induced trait changes in perch strongly increased pike recruitment success and reversed the respective rank of pike and perch in the dominance hierarchy. Our results do support the view that synergies occur in nature, are potentially common, and can profoundly influence community functioning. In particular, synergies provide a mechanism through which invading pathogens and predators can durably integrate into an ecosystem.