Functionally redundant multimodal predator cues elicit changes in prey foraging behavior

Many prey species can assess the risk of predation from information acquired through different sensory systems. For many animals, this information is detected with sensory organs specialized for visual (sight) or chemical (smell or taste) stimuli. It is unclear; however, whether information acquired through multiple sensory systems is functionally redundant or interchangeable, especially if the message is the same. Here, we assess prey response to unimodal visual and chemical cues as well as multimodal (visual + chemical) cues. We specifically test if a foraging individual shows a stronger behavioral response to risk when they can perceive that risk through multimodal versus unimodal cues. To do this, we measured the functional response (prey abundance–foraging rate relationship) of Tibellus oblongus spiders foraging on midges while exposing them to visual stimuli, chemical stimuli, or a combination of both visual and chemical stimuli from potential predators. We then determined if the spider’s functional response for the multimodal treatment differed more strongly from a control treatment than from either unimodal treatment. We found that under any simulated predation risk (multimodal and both unimodal), T. oblongus spiders showed longer handling times than in control groups without risk. However, we saw no elevated anti-predator response in the multimodal treatment, suggesting that information from visual and chemical modalities is interchangeable and sufficient to indicate reliably predation risk.