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In multitrophic systems, top predators influence the abundance and biomass of lower trophic levels. Top-down control through predation is important for regulating ecosystems. In addition to consumption, predators also alter the behaviour, life-history, and morphology of prey species. This trait-mediated interaction is a response to predation risk and can indirectly reduce reproductive fitness as prey species change patterns of energy uptake and allocation. These combined direct and indirect predator-control pathways are understood to be widespread. Here, we investigated the role of trait-mediated interactions in a marine tri-trophic food chain: an echinoderm top predator (Crossaster papposus) and echinoderm mesopredator (Asterias rubens), and a molluscan basal prey species (Mytilus edulis). We exposed the mesopredator to cues from the top predator and the prey species and analysed movement patterns in a mesocosm experiment. We found no statistically significant differences between different cue combinations (control, top predator only, prey only, combined predator and prey cues). This suggests that trait-mediated interactions can be context-dependent, and that “fear effects” may not always be the primary driver of movement, though caution is warranted when extrapolating beyond the present experimental conditions.
Smith et al. (Mon,) studied this question.