Data from: Vegetation structure mediates a shift in predator avoidance behavior in a range-edge population

Where organisms encounter novel conditions during range expansion, behavioral changes suited to the new habitat can enhance survival. Behavioral changes that mitigate predation risk are particularly important for the persistence of range-edge populations, especially where plastic responses outpace genetic adaptation. We use a climate-driven spatial mismatch between the arboreal mangrove tree crab (Aratus pisonii) and its primary mangrove habitat to evaluate differences in predator avoidance behavior between populations in range-center mangroves and adjacent range-edge salt marshes. We expected that differences in vegetation stature and diameter mediate changes in Aratus behavior. We combined crab and vegetation surveys with tethering experiments and in situ behavioral trials to determine habitat-specific predation risk and predator avoidance via evasion and autotomy. Tethering trials revealed that predation risk was always greater from aquatic sources than terrestrial sources and that aquatic risk was enhanced in marsh habitat. Vegetation structural form constrained Aratus predator avoidance during in situ behavioral assays: in mangroves, Aratus escaped upward into the canopy, but short statured marsh grass restricted evasion to downward movement towards the higher risk aquatic environment. Given this restricted evasion route, Aratus in salt marsh were less likely to evade and showed more evidence of secondary escape via leg-dropping. Shifting predator avoidance behavior away from a fleeing escape strategy may ameliorate the fitness costs of reduced escape opportunities for Aratus in novel marsh habitat along the range-edge. Similar changes in behavior to match local habitat conditions could be integral to the persistence of many range-edge populations that encounter novel habitats.

当生物在种群扩张过程中遭遇全新环境时，适配新栖息地的行为变化可提升其生存概率。其中，能够降低捕食风险的行为改变对分布边缘种群的存续尤为关键，尤其是当表型塑性响应的速度超过遗传适应时。

我们以气候驱动的树栖红树林蟹（Aratus pisonii）与其主要红树林栖息地之间的空间错配为研究对象，对比分析分布中心红树林种群与邻近分布边缘盐沼种群的避敌行为差异。我们推测，植被高度与直径的差异会调控该蟹类的行为变化。

我们结合蟹类与植被调查、栓系实验（tethering experiments）以及原位行为试验，通过逃避与自切（autotomy）行为来评估不同栖息地的捕食风险与避敌策略。

栓系试验结果显示，水生来源的捕食风险始终高于陆生来源，且盐沼生境中的水生捕食风险更高。植被结构限制了该蟹类在原位行为试验中的避敌行为：在红树林生境中，它们可向上逃窜至树冠层；但低矮的盐沼草本植物将其逃避路径限制为朝向高风险水生环境的向下移动。鉴于逃避路径受限，盐沼生境中的该类蟹类更难实施逃避行为，且更多表现出通过断腿实现的次级逃逸策略。

放弃逃跑型逃避策略的避敌行为转变，可缓解分布边缘新生盐沼生境中该蟹类因逃逸机会减少带来的适合度成本。这类匹配当地生境条件的行为改变，或许是众多遭遇新生栖息地的分布边缘种群得以存续的核心机制。