دانلود مقاله : Defensive posture and eyespots deter avian predators from attacking caterpillar mod

چکیده : 

Many lepidopteran caterpillars appear to gain protection from insect-eating birds because they possess

eyespots, a pair of conspicuous markings on the body generally thought to resemble the eyes of a

predator. Similarly, many caterpillars widen their anterior body segments when threatened, and this

defensive posture may also deter attack because it emphasizes the caterpillar’s eyes and/or allows the

caterpillar to resemble a snake more closely. Yet, given that this behaviour is not limited to caterpillars

with eyespots, it is possible that the defensive posture may serve as a predator deterrent in itself. To

disentangle the protective value of eyespots and widened anterior body segments, we created four types

of artificial caterpillar in a 22 factorial design and deployed them on tree branches in the field where

they were exposed to predation attempts by wild birds. The ‘survivorship’ of the artificial caterpillars was

monitored over 90 h in six locations.We found a clear survival advantage for artificial prey with eyespots

or a widened head shape. However, prey possessing both eyespots and a widened head did not survive

longer than prey with either characteristic alone, suggesting that the traits did not act synergistically to

deter attack. Interestingly though, only caterpillars in the eyespot-defensive posture treatment received

more pecks directed towards the anterior ‘head’ region. Collectively, this study demonstrates clearly that

caterpillars possessing either eyespots or widened anterior body segments are likely to experience

reduced predation by wild birds, even at northern latitudes where there are relatively few arboreal

snakes.