Threat-sensitive preator avoidance behavior

The threat-sensitive predator avoidance hypothesis predicts that prey are able to assess the magnitude of predator threat and adjust their behavior accordingly. This hypothesis has been tested in classical predator-prey interactions between trophic levels but not in predator-predator interactions within a trophic level such as intraguild predation (IGP). IGP is defined as predation between potential competitors. Numerous recent studies revealed that IGP is common among plant-inhabiting predatory mites of the family Phytoseiidae. Most studies on IGP among phytoseiid mites focused on the predator`s part whereas information on the prey`s part, i.e. detection and avoidance of IG predators, is scarce. We propose to test the threat sensitive predator avoidance hypothesis in a phytoseiid guild, consisting of the diet-specialist Phytoseiulus persimilis and the diet-generalists Neoseiulus californicus and Amblyseius andersoni. All three species are predators of herbivorous spider mites and important biological control agents. Based on current knowledge we tentatively rank these species P. persimilis

Behaviors helping prey to avoid being killed by a predator are termed anti-predation behaviors. Every anti- predation behavior is energetically demanding and, thus, has not only benefits but also costs. The threat-sensitive predator avoidance hypothesis predicts that prey animals are able to assess the magnitude of predator threat and adjust their behaviors accordingly. Both overreacting and non-responding prey would incur a fitness decrease, i.e. decreased survival probabilities and/or reproduction. This concept has been supported by numerous observations of graded anti-predator responses from both vertebrates and invertebrates in classical predator-prey interactions but has never been tested for predator-predator interactions within a trophic level such as intraguild predation (IGP). We studied the predictions of the threat-sensitive predator avoidance hypothesis and the role of experience in shaping anti-predation behaviors in a natural guild of predatory mites, Phytoseiulus persimilis, Neoseiulus californicus and Amblyseius andersoni, co-occuring in the Mediterranean region. All three species prey on spider mites but differ greatly in diet specificity with P. persimilis being highly specialized, N. californicus being intermediate and A. andersoni being the least specialized. The ranking regarding their propensity to IGP is: A. andersoni > N. californicus > P. persimilis with the larvae being the most vulnerable to IGP, and the adult females being the most dangerous IG predators. In general, IGP risk of larvae may be reduced by the larvae themselves or by maternal oviposition site selection. Our experiments revealed that P. persimilis females reduced egg production in spider mite patches containing IG predator cues. Only experienced P. persimilis females responded in a threat- sensitive way and deposited nearly all eggs in the predator free spider mite patches. N. californicus females were threat-sensitive in egg laying irrespective of experience, whereas A. andersoni did not respond to predation risk. Similar threat-sensitivities were observed in larval IG prey. Larval IG prey of P. persimilis showed two different strategies when confronted with a low and high risk IG predator. In the presence of the low risk IG predator they responded with typical escape behavior, whereas they reduced activity in the presence of the high risk IG predator. To the best of our knowledge, our study is the first experimental documentation that IG prey and their mothers are able to discriminate IG predator species posing different risks and respond in threat-sensitive ways to reduce IGP risk. Since the three studied predators are important natural enemies of herbivorous mites and insects, the outcome of our project contributes to optimize their use in natural and biological control.