Phenotypic plasticity in anti-intraguild predator strategies: mite larvae adjust their behaviours according to vulnerability and predation risk

Interspecific threat-sensitivity allows prey to maximize the net benefit of antipredator strategies by adjusting the type and intensity of their response to the level of predation risk. This is well documented for classical prey-predator interactions but less so for intraguild predation (IGP). We examined threat-sensitivity in antipredator behaviour of larvae in a predatory mite guild sharing spider mites as prey. The guild consisted of the highly vulnerable intraguild (IG) prey and weak IG predator Phytoseiulus persimilis, the moderately vulnerable IG prey and moderate IG predator Neoseiulus californicus and the little vulnerable IG prey and strong IG predator Amblyseius andersoni. We videotaped the behaviour of the IG prey larvae of the three species in presence of either a low- or a high-risk IG predator female or predator absence and analysed time, distance, path shape and interaction parameters of predators and prey. The least vulnerable IG prey A. andersoni was insensitive to differing IGP risks but the moderately vulnerable IG prey N. californicus and the highly vulnerable IG prey P. persimilis responded in a threat-sensitive manner. Predator presence triggered threat-sensitive behavioural changes in one out of ten measured traits in N. californicus larvae but in four traits in P. persimilis larvae. Low-risk IG predator presence induced a typical escape response in P. persimilis larvae, whereas they reduced their activity in the high-risk IG predator presence. We argue that interspecific threat-sensitivity may promote co-existence of IG predators and IG prey and should be common in predator guilds with long co-evolutionary history.