MacLeod Colin D, Luong Lien T
Department of Biological Sciences, University of Alberta, CW405 Biological Sciences Building, Edmonton, AB, T6G 2E9, Canada.
Oecologia. 2025 May 6;207(5):79. doi: 10.1007/s00442-025-05722-3.
The presence of natural enemies can cause organisms to change habitat use, foraging behavior, and/or resource allocation in response to a perceived risk, responses that may come at the cost of other fitness-related traits. Since most species encounter multiple natural enemies in nature, defensive behaviors against one attacker may make the focal organism more vulnerable to attack by a different natural enemy. Anti-predator behaviors can lead to trait-mediated indirect effects, such as an increased risk of parasitism and vice versa. Few empirical studies have examined the response of a single focal species to the risk of attack by multiple species. Our experiments provided the cactiphilic fly Drosophila nigrospiracula with opportunities to prioritize either anti-predator (e.g., reduced activity) or anti-parasite behavior (e.g., increased activity) at the cost of increased infection or predation, respectively. We experimentally show that when flies were exposed to ectoparasitic mites, in the presence of predator (jumping spider) cues, flies incurred increased levels of infection compared to flies without predator cues. The mean infection prevalence increased by 80% and the infection intensity increased by 180%. However, the presence of parasite cues had no analogous effect on predation rates, which suggests that flies prioritized predation risk over parasite defense at the cost of increased infection. We provide empirical evidence that the presence of multiple threats can lead to trait-mediated indirect effects, with important consequences for host-parasite and food web dynamics, and the ecology of fear.
天敌的存在会使生物体为应对感知到的风险而改变栖息地利用方式、觅食行为和/或资源分配，这些反应可能会以牺牲其他与适应性相关的特征为代价。由于大多数物种在自然界中会遇到多种天敌，针对一种攻击者的防御行为可能会使目标生物体更容易受到另一种天敌的攻击。反捕食者行为会导致性状介导的间接影响，例如寄生虫感染风险增加，反之亦然。很少有实证研究考察单一目标物种对多种物种攻击风险的反应。我们的实验为嗜仙人掌果蝇Drosophila nigrospiracula提供了机会，使其能够分别以增加感染或被捕食的代价来优先选择反捕食者行为（例如降低活动水平）或抗寄生虫行为（例如增加活动水平）。我们通过实验表明，当果蝇暴露于体外寄生螨时，在有捕食者（跳蛛）线索的情况下，与没有捕食者线索的果蝇相比，果蝇的感染水平会增加。平均感染率增加了80%，感染强度增加了180%。然而，寄生虫线索的存在对捕食率没有类似影响，这表明果蝇以增加感染为代价，将捕食风险置于寄生虫防御之上。我们提供了实证证据，证明多种威胁的存在会导致性状介导的间接影响，这对宿主 - 寄生虫和食物网动态以及恐惧生态学具有重要影响。
