Odours of non-predatory species help prey moderate their risk assessment

Prey use contemporary information to update their risk estimation, and accordingly, optimize their anti-predator reactions. Conceptualization of this process is largely focused on information that reflects predator activity. We aimed to complement this unilateral view by testing whether prey also use cues of non-predatory species to update their risk perception. We focused our investigation on the desert isopod Hemilepistus reaumuri that reacts defensively to excavated soil mounds even in the absence of direct predator cues. We located in the field 19 isopod burrows and surrounded each with six soil mounds. One mound remained odourless and the other five were supplemented by odours of a major isopod predator, the golden scorpion, and four sympatric species that do not prey on isopods but excavate soil. Isopods augmented their defensive responses towards mounds supplemented by scorpion odours and lessened their anti-predator reactions towards mounds with odours of herbivore rodents. Isopods’ responses to the odours of the two insectivorous species that do not eat isopods were similar to the reaction towards the odourless control mounds. Our results suggest that prey use non-predatory species cues to moderate their risk estimation. Therefore, we need to consider this potentially important source of information in studies of predator–prey interactions. Our findings also indicate that odours or vocalization of non-predatory species may not be adequate as control treatments to predator cues. A free Plain Language Summary can be found within the Supporting Information of this article.