Insights into how predator diversity, population density and habitat type may affect defensive behaviour in a Mediterranean lizard

Various factors may alter anti-predatory responses among conspecifics. Here we assess some of these factors using three populations of a Mediterranean lizard (<i>Acanthodactylus schreiberi</i>) in Cyprus that differ in their habitat type, predator diversity and population density. We expected that predation would affect flight initiation distance (FID; the approach distance allowed to an observer before the lizard flees), escape distance (ED; the distance covered by the lizard from the point an escape attempt starts to the first place the lizard stops) and tail autotomy (autotomy rates, economy of autotomy, post-autotomy tail movement). We also predicted that juveniles, being more exposed to predators, would be more effective in their defensive responses. Our findings suggest that predation and population density appear to be associated with most autotomy traits but were not associated with FID and ED, which are better explained by refuge availability. The only ontogenetic difference was detected in the economy of autotomy: juveniles are more prone to autotomise, possibly because they do not experience such high costs as tailless adult individuals. Our results suggest that anti-predatory responses are influenced by a variety of factors. Unravelling the compound effects of all the factors involved should be the focus of future research.

多种因素可改变同种个体间的反捕食响应。本研究以塞浦路斯境内的三种地中海蜥蜴种群——<i>Acanthodactylus schreiberi</i>——为研究对象，这些种群在生境类型、捕食者多样性以及种群密度上存在差异，借此评估其中部分影响因素。我们预测捕食压力会影响逃逸起始距离（flight initiation distance, FID，即观察者逼近至蜥蜴逃逸时的最大距离）、逃逸距离（escape distance, ED，即蜥蜴从开始逃逸到首次停下时所移动的距离）以及尾部自断行为（包括自断率、自断经济性以及自断后尾部摆动行为）。我们还预测：由于幼体面临更高的捕食暴露风险，其防御响应会更为高效。研究结果显示，捕食压力与种群密度似乎与多数尾部自断相关性状存在关联，但与FID和ED无显著相关性，而后两者更易由避难所可获得性来解释。仅在自断经济性上发现了显著的个体发育差异：幼体更易发生尾部自断，这可能是因为幼体无需像无尾成体那样承担高昂的断尾代价。本研究结果表明，反捕食响应受多种因素共同调控，解析所有相关因素的复合效应应成为未来研究的核心方向。