Department of Ecology and Evolutionary Biology, University of California Santa Cruz, 130 McAllister Way, Santa Cruz, CA, 95060, USA.
East Bay Municipal Utility District, 1 Winemaster Way, Lodi, CA, 95240, USA.
Oecologia. 2021 Sep;197(1):89-100. doi: 10.1007/s00442-021-05008-4. Epub 2021 Aug 5.
Environmental conditions strongly affect antipredator behaviors; however, it is less known how migrating prey adjust antipredator behavior in migration corridors, in part, because active migrants are difficult to observe and study. Migrants are vulnerable and encounter many predators in the corridor, and their propensity to travel towards their destination ties antipredator behavior with movement. We evaluated how environmental risk cues in the migration corridor including in-water habitat structure (present, absent) and overhead shade (sun, shade), and salmon origin (hatchery, wild) affected how juvenile Chinook salmon (Oncorhynchus tshawytscha) reacted to a live predator. We measured how salmon react to predation risk as the difference in time to swim downstream through a 9.1-m long field enclosure with or without a live predatory largemouth bass (Micropterus salmoides). Shade significantly modified the reaction to the predator, and it did so in two ways. First, the magnitude of antipredator behavior was larger in shade compared to direct sun, which suggests salmon perceived shade to be a riskier environment than sun. Second, the escape tactic also varied; salmon slowed down to be cautious in shade and sped up in sun. Structure did not significantly affect behavior and hatchery and wild salmon behaved similarly. Our study suggests that environmental risk cues can shape the magnitude and tactics of how migrants react to predation risk and illustrates how these responses relate to movement with potential to scale up and affect migration patterns.
环境条件强烈影响着捕食者防御行为；然而，人们对于迁徙过程中的猎物如何调整捕食者防御行为知之甚少，部分原因是活跃的迁徙者难以观察和研究。迁徙者很脆弱，在迁徙走廊中会遇到很多捕食者，它们向目的地迁徙的倾向将捕食者防御行为与运动联系起来。我们评估了迁徙走廊中的环境风险线索，包括水中栖息地结构（存在、不存在）和头顶遮荫（阳光、遮荫）以及鲑鱼的来源（孵化场、野生）如何影响幼年奇努克鲑鱼（Oncorhynchus tshawytscha）对活体捕食者的反应。我们测量了鲑鱼在有或没有活体掠食性大口黑鲈（Micropterus salmoides）的情况下，通过 9.1 米长的野外围栏下游游的时间差异，来衡量鲑鱼对捕食风险的反应。遮荫显著改变了对捕食者的反应，而且有两种方式。首先，与直接阳光相比，在遮荫下鲑鱼的防御行为幅度更大，这表明鲑鱼认为遮荫环境比阳光更具风险。其次，逃避策略也有所不同；鲑鱼在遮荫下会减速以保持谨慎，而在阳光下会加速。结构对行为没有显著影响，孵化场和野生鲑鱼的行为相似。我们的研究表明，环境风险线索可以塑造迁徙者对捕食风险的反应的幅度和策略，并说明了这些反应如何与运动相关，具有潜在的放大和影响迁徙模式的能力。
