Considerations Used by Desert Isopods to Assess Scorpion Predation Risk

Abstract

Animals adjust behaviors to balance changes in predation risk against other vital needs. Animals must therefore collect sensory information and use a complex risk-assessment process that estimates risks and weighs costs and benefits entailed in different reactions. Studying this cognitive process is challenging, especially in nature, because it requires inferring sensory abilities and conscious decisions from behavioral reactions. Our goal was to address this empirical challenge by implementing psychophysical principles to field research that explores considerations used by desert isopods (Hemilepistus reaumuri) to assess the risk of scorpions that hunt exclusively from within their burrows. We introduced various combinations of chemical and physical cues to the vicinity of isopod burrows and recorded their detailed reactions on first encountering the cues. The isopods reacted defensively to scorpion odor but only when accompanied with excavated soil or other odors typically found near scorpion burrows. Isopods also reacted defensively to piles of excavated soil without scorpion olfactory cues, suggesting that isopods take precautions even against physical disturbances that do not necessarily reflect predator activity. Simultaneous presence of different cues provoked graded responses, possibly reflecting an additive increase in risk estimation. We conclude that wild isopods use defensive reactions toward environmental signals only when the integrated perceptual information implies an active scorpion burrow or when they lack data to refute this possibility.

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

“…Isopods have poor eyesight and use their antennae's contact chemoreceptors to locate food, recognize kin, identify their burrow‐specific scent and detect predation cues (Hoffmann, ; Linsenmair, ; Warburg, ). Therefore, perception distances are considered to be of antennae length from the isopod's body, preventing isopods from estimating the size of large objects (>2 cm) without further inspection (Zaguri et al, ). During July, isopods forage mostly during a short time‐window of approximately 2 hr after dawn and remain within their burrow for the rest of the day.…”

“…We added field‐trapped S. palmatus scorpions to 19 randomly chosen containers, and immediately fed each scorpion with a single field‐trapped isopod. In this way, we mimicked the composite olfactory signals expected to be found near an active scorpion burrow (Zaguri et al, ). To 19 additional containers we added field‐collected B. israelis scorpions.…”

“…Prey animals use costly defensive behaviours at the expense of other beneficial activities to mitigate predation risks (Lima & Bednekoff, ; Lima & Dill, ; Zaguri, Zohar, & Hawlena, ). Predation risks vary greatly over space and time (Palmer, Fieberg, Swanson, Kosmala, & Packer, ; Sih, ) forcing the prey to constantly adjust their antipredator behaviour to match those changes (Helfman, ; Lima & Bednekoff, ; Lima & Dill, ).…”

“…Predation risks vary greatly over space and time (Palmer, Fieberg, Swanson, Kosmala, & Packer, ; Sih, ) forcing the prey to constantly adjust their antipredator behaviour to match those changes (Helfman, ; Lima & Bednekoff, ; Lima & Dill, ). To avoid excessive costs of defensive overreaction or the mortal danger of underestimating predation, prey must accurately and reliably estimate the risk using updated perceptual information (Blumstein & Bouskila, ; Zaguri et al, ).…”

“…Nevertheless, experimental evidence shows that isopods respond defensively to these ambiguous cues even in the absence of additional predator cues, possibly reflecting overestimation of risk (Zaguri et al, ). When ‘confirmation cues’, such as scorpion odours, were experimentally added to the soil mounds, isopods intensified their anti‐predatory responses, possibly reflecting the enhanced risk estimation (Zaguri et al, ). This experimental system therefore, provides an excellent opportunity to take the next step and test whether adding olfactory cues from non‐predatory species to an excavated soil mound serves as a safety cue and alleviates the isopods’ overestimation of risk.…”