Fearless distasteful butterflies and timid mimetic butterflies: comparison of flight initiation distances in Papilioninae

Prey are expected to flee from an approaching predator when the cost of remaining (i.e. being captured) exceeds the cost of fleeing. In species where individuals experience less predation pressure, delayed escape responses to predatory threats are predicted. Therefore, non-chalant behaviour should be observed in unpalatable and Batesian mimetic prey while rapid escape behaviour may be displayed in palatable and non-mimetic prey from closely related species. This study compared the flight initiation distances (FIDs; the distances at which a prey starts to flee during a standardized human approach) of several sympatric swallowtail butterflies (Papilionidae) in two areas with different temperate zones. As predicted, it was found that unpalatable species had significantly shorter FIDs than palatable species in both areas. By contrast, FIDs of Batesian mimic species were significantly longer than those of unpalatable model species and were not significantly different from those of palatable species. FIDs were not significantly different between mimetic and non-mimetic forms of the intraspecific polymorphic species Papilio polytes. The mimetic species or form may reduce the risk of revealing their identity (i.e. palatability) through early escape behaviour. These findings have implications for the selective forces that affect the escape tendency of prey.

Escape behaviour of aposematic (Oophaga pumilio) and cryptic (Craugastor sp.) frogs in response to simulated predator approach

Crypsis and aposematism are common antipredator strategies that can each be coupled with behaviours that maximize predator deterrence or avoidance. Cryptic animals employ camouflage to conceal themselves within their environment and generally rely on immobility to avoid detection by predators. Alternatively, aposematic animals tend to rely on an association between conspicuous colouration and secondary defence to deter potential predators, and tend to exhibit slow movements in response to predators. The goal of the present study was to determine how cryptic Craugastor sp. and aposematic Oophaga pumilio respond to simulated human and bird model predators. Oophaga pumilio responded more often with movement to both the human (17/22) and bird (9/25) predators than Craugastor sp. (human: 2/21; bird: 0/21). The increased movement resulted in a greater average flight initiation distance, latency to move, and distance fled in O. pumilio. These findings suggest that cryptic Craugastor sp. rely on immobility to avoid detection, whereas aposematic O. pumilio utilize movement, possibly as a mechanism to increase the visibility of their warning signals to potential predators. Furthermore, O. pumilio exhibited greater movement in response to humans, suggesting that they actively avoid trampling by large threats, rather than considering them predators.

Fleeing to refuge: Escape decisions in the race for life

Economic escape theory that predicts that flight initiation distance (FID=predator-prey distance when a prey begins to flee from an approaching predator) increases as predation risk increases has been overwhelmingly supported. However, the vast majority of empirical tests have focused on effects of single predation risk factors. Even studies that have included multiple risk factors have not predicted how they jointly affect FID. I present a model that predicts joint effects of several predation risk factors that affect the outcome of a race between predator and prey to the prey's refuge. As a prey's distance to refuge and predator attack speed increase, and as the prey's location forces it to flee more toward a predator to reach refuge, FID increases. A published model proposed and experiment showed that FID is longer when prey flee directly toward than directly away from a predator to a refuge. We present a new geometric model that predicts FID for all angles between the prey's and predator's paths to refuge, distance of the prey from refuge when escape begins, predator and prey speeds, and a margin of safety allowing the prey to reach refuge before the predator. The model provides many new, testable predictions about relationships among its variables and FID. Most notably, it predicts that FID increases sigmoidally as the angle between predator and prey paths to refuge increases. Although the model is not economic (cost-benefit), we discuss its relationship to economic escape theory.