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 (Acanthodactylus schreiberi) 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3个舒氏棘趾蜥（Acanthodactylus schreiberi）种群为研究对象，这些种群在生境类型、捕食者多样性及种群密度上存在差异，借此评估部分相关影响因素。我们推测捕食作用会对逃逸起始距离（flight initiation distance, FID，即观察者接近至蜥蜴逃逸前的最大距离）、逃逸距离（escape distance, ED，即蜥蜴从启动逃逸至首次停下的位点间所移动的距离）以及断尾自割行为（自割率、自割经济性、自割后尾部运动情况）产生影响。我们同时预测，由于幼体更易遭遇捕食者，其防御响应会更为高效。研究结果显示，捕食作用与种群密度似乎与多数断尾自割性状相关，但与逃逸起始距离和逃逸距离并无关联，后两者更易受避难所可获得性的解释。仅在断尾自割经济性上发现了个体发育差异：幼体更倾向于发生断尾自割，这可能是因为它们不会像无尾成体那样承受高昂的代价。本研究结果表明，反捕食响应受多种因素共同影响。未来研究应聚焦于厘清所有相关因素的复合效应。