Network structure and species connectivity drive asymmetric fitness outcomes in coevolving antagonistic communities

Pablo Gallarta Sáenz , Santiago Lamata Otín, Jesús Gómez Gardeñes, Cecilia S. Andreazzi

Antagonistic interactions are fundamental drivers of ecological community structure, generating strong reciprocal selective pressures that shape the evolution of functional traits across interacting species. Despite their ecological importance, the coevolutionary dynamics of antagonistic communities remain far less understood than those of mutualistic systems. Here, we develop a trait-based coevolutionary model in which exploiters and victims evolve under symmetric dynamical equations governed by two additive selective forces: a stabilising component directed towards a species-specific environmental optimum, and a directional component arising from antagonistic interactions within the ecological network. Using this framework alongside a trait-based fitness measure, we show that connectivity shapes fitness asymmetrically across guilds: generalist exploiters outperform specialists under weak interaction-driven selection while the advantage reverses under strong selection, whereas victim fitness is buffered by exposure to multiple exploiters through selective dilution. A principal component analysis of structural network descriptors further reveals that global network architecture predicts community-level exploiter fitness only under regimes of reciprocal antagonistic selection, while victim fitness remains largely insensitive to network structure. Together, these results demonstrate that antagonistic coevolutionary asymmetries are emergent consequences of the interplay between opposing selective pressures and the ecological networks through which they propagate, with implications for predicting the eco-evolutionary consequences of anthropogenic change.