Predator type, not body condition, influences positioning within whirligig groups

摘要

The anti-predator responses of an animal may depend on the species of predator attacking. For example, ground-dwelling monkeys respond with different warning calls in response to attacks from hawks from above vs attacks from leopards at the side. In grouping animals, it has usually been assumed that the best anti-predator behavior against most predators is to move toward the center of a group. However, little work has been done to study positioning of individuals in response to different predators and whether it might be influenced by gender or body condition. An optimality model is developed that gives predictions for how the needs of predator avoidance, drafting, and foraging could lead to one optimal location within the group. We then conducted a laboratory experiment with individually marked whirligig beetles (Coleoptera: Gyrinidae). We exposed them to an aerial (bird) or aquatic (fish) attack and determined changes in their distance to the front of groups at different speeds of water. We found that female whirligigs occupied the front of a group in response to a fish attack in fast water, but the back after an aerial bird attack, while the reverse was true for males. In slow water, different results were found; in response to a bird attack, females were more likely to be found in the front compared with males. Body condition was not correlated to the front/back position of either males or females before or after attacks in our study. Keywords Grouping - Optimality - State-dependent - Sexual segregation - Predator avoidance - Gyrinidae Communicated by D. Gwynne