Abstract
Some animals show multiple behavioral responses after detection of chemical cues indicating a predation threat. Individuals of the high intertidal periwinkle, Littorina sitkana, showed two contrasting anti-predation responses, immobile cautiousness and active fleeing, against the predatory crab, Hemigrapsus sanguineus. This study examined the combined effects of chemical cues of predation threat (crab, crushed conspecific, mixed crab and crushed conspecific, and control), body size, and time (morning, mid-day and late-evening) on the anti-predation behaviors of L. sitkana. The cautious response of L. sitkana was strongest under the crab treatment, with the earliest fleeing response appearing when presented with the mixed chemical cue of crabs and crushed conspecifics. Time of day also affected the anti-predation responses, with a longer cautious response during late-evening than mid-day under control conditions, and no significant difference between late-evening and mid-day in response to the three types of chemical cues of predation threat. The fleeing response occurred more rapidly during late-evening than mid-day for the four types of chemical conditions; there was no significant difference between morning and mid-day under the control condition; and it occurred more rapidly during morning than mid-day under the three predation threat conditions. Larger individuals showed longer cautious responses for all conditions and remained submerged in seawater for longer under the three predation threat conditions. It is suggested that the level of predation risk may be assessed by L. sitkana and used to elicit the appropriate of the two contrasting anti-predation responses.
