Behavioral plasticity and the valence of indirect interactions

Behavioral plasticity in animals often transforms direct interactions between species, but its effects can spread through ecological networks in unexpected ways, creating indirect interactions that are difficult to predict. We present a theoretical framework to understand how species-level behavioral changes influence these indirect interactions and the overall dynamics of ecological networks. As an illustrative example, we analyze predators that feed on two types of prey, each of which temporarily transitions into a state of reduced activity and growth after evading an attack, to decrease vulnerability. Coarse-grained models show that this hiding behavior can shift the indirect interaction between prey species from apparent competition to mutualism or parasitism. These shifts occur when the predator's capture efficiency falls below a threshold, causing frequent hunting failures. This inefficiency leads to one prey species indirectly protecting the other by drawing predator attention, paradoxically increasing predator biomass due to reduced hunting success. Interestingly, empirical capture probabilities align with the range where such shifts are predicted. We describe these changes in the qualitative nature of species interactions as shifts in "interaction valence," emphasizing how routine animal behaviors can generate indirect effects that defy intuition and reshape community structure through cascading effects across the network.