Interplay of trophic relaxation and directional selection shapes eco-evolutionary responses to selective harvest in predator-prey systems

Fisheries-Induced Evolution (FIE) describes the evolutionary changes in life-history traits exhibited by target species in response to selective fishing pressures. Current studies predominantly focus on single-species contexts, often assuming stationary natural selection and neglecting the impact of interacting species. In this study, using an eco-evolutionary predator-prey model, we demonstrate that the presence of interacting species can fundamentally modify, or even reverse, the evolutionary responses of target species to fisheries. Specifically, we show that target species can evolve to exhibit larger body sizes, even when fisheries preferentially target large individuals. A novel mechanism is proposed to elucidate this counterintuitive outcome. Fisheries influence the evolutionary adaptation of target species through both direct and indirect pathways. The direct pathway, termed “directional selection”, occurs when fisheries selectively target individuals with specific characteristics, thereby distorting the fitness landscape, akin to processes observed in single-species systems. The indirect pathway, referred to as “trophic relaxation”, depicts that fisheries weaken the predator-prey trophic link, subsequently altering the coevolutionary dynamics between predator and prey. These pathways can operate concurrently, leading to either antagonistic or synergistic evolutionary outcomes, which depend on the coevolutionary dynamics of the predator-prey system, harvest patterns, and the selectivity of fishing gear. Our findings highlight that the evolutionary responses of target species to fisheries selection are variable and significantly influenced by both the interactions among species and fishing activities.

Methods
In this study, we create an eco-evolutionary predator-prey system with mathematical analysis to investigate the evolutionary responses of target species to selective harvesting under the influence of non-target species.

Here, we provide our simulation code, written with R, and simulation data. With the code and data, our result can be reproduced.