Moshe Zaguri, Dror Hawlena
Imagine walking near a swamp at night when suddenly the chirping frogs go quiet. Why do we immediately become more alert? We explain this sudden change in risk perception by hypothesizing that prey, when approaching an area that may harbor risks, use non-predatory species cues to moderate their fear (in this case, chirping frogs indicate a safe – predator-free – environment). As of today, conceptualization of the risk assessment process is primarily focused on information that reflects predator activity. We aimed to complement this unilateral view by testing whether prey also use ‘safety cues’ such as the odor of non-predatory species to update their risk perception.
We tested this novel hypothesis in the field by exposing desert isopods to excavated soil mounds that were accompanied by odors of predatory and non-predatory species and comparing their defensive reactions. Similar mounds are typically found outside the burrows of the isopods’ main predator (the Israeli golden scorpion) but are also created by many other animals that do not feed on isopods. Isopods react defensively to these mounds even in the absence of additional predator cues. This experimental system, therefore, provides an excellent opportunity to test whether the addition of olfactory cues from non-predatory species to an excavated soil mound serves as a safety cue and alleviates the isopods’ estimation of risk.
We showed that isopods treated the odorless control mounds with caution and intensified their defensive reactions toward soil mounds with odors of their scorpion predator. Isopods alleviated their defensive responses toward soil mounds supplemented with odors of non-predatory species, reflecting a reduced risk assessment. Interestingly, the responses of isopods to soil mounds supplemented with odors of carnivores that do not feed on isopods did not differ from the reactions to odorless control mounds. Our results suggest that prey animals do not rely solely on predator cues to update their risk assessments, but also use ‘safety cues’ from non-predatory species. These findings also question the customary use of odors or vocalization of non-predatory species as a control treatment to predator cues.