UPMC-Paris 6, UMR (CNRS) 7618, Laboratoire Biogéochimie et Ecologie des Milieux Continentaux, Ecole Normale Supérieure, 46 rue d'Ulm, 75230 Paris cedex 05, France.
Proc Biol Sci. 2010 Mar 22;277(1683):843-51. doi: 10.1098/rspb.2009.1724. Epub 2009 Nov 18.
Chronic social stress diverts energy away from growth, reproduction and immunity, and is thus a potential driver of population dynamics. However, the effects of social stress on demographic density dependence remain largely overlooked in ecological theory. Here we combine behavioural experiments, physiology and population modelling to show in a top predator (pike Esox lucius) that social stress alone may be a primary driver of demographic density dependence. Doubling pike density in experimental ponds under controlled prey availability did not significantly change prey intake by pike (i.e. did not significantly change interference or exploitative competition), but induced a neuroendocrine stress response reflecting a size-dependent dominance hierarchy, depressed pike energetic status and lowered pike body growth rate by 23 per cent. Assuming fixed size-dependent survival and fecundity functions parameterized for the Windermere (UK) pike population, stress-induced smaller body size shifts age-specific survival rates and lowers age-specific fecundity, which in Leslie matrices projects into reduced population rate of increase (lambda) by 37-56%. Our models also predict that social stress flattens elasticity profiles of lambda to age-specific survival and fecundity, thus making population persistence more dependent on old individuals. Our results suggest that accounting for non-consumptive social stress from competitors and predators is necessary to accurately understand, predict and manage food-web dynamics.
慢性社会压力会转移生物生长、繁殖和免疫的能量，因此是影响种群动态的一个潜在驱动因素。然而，社会压力对种群密度制约的影响在生态学理论中仍很大程度上被忽视。在这里，我们结合行为实验、生理学和种群模型，以顶级掠食者（梭鲈 Esox lucius）为例，表明单独的社会压力可能是种群密度制约的主要驱动因素。在受控猎物供应条件下，将实验池塘中的梭鲈密度增加一倍，并不会显著改变梭鲈的猎物摄入量（即不会显著改变干扰或掠夺性竞争），但会引起神经内分泌应激反应，反映出一种与体型相关的支配等级，使梭鲈的能量状态下降，身体生长速度降低 23%。假设使用针对英国温德米尔（Windermere）梭鲈种群的固定体型相关生存和繁殖功能参数化，应激诱导的体型变小会改变特定年龄的存活率，并降低特定年龄的繁殖力，这会导致 Leslie 矩阵中的种群增长率（lambda）降低 37-56%。我们的模型还预测，社会压力会使 lambda 对特定年龄的存活率和繁殖力的弹性曲线变平，从而使种群的持续生存更加依赖于老年个体。我们的研究结果表明，为了准确理解、预测和管理食物网动态，有必要考虑来自竞争者和捕食者的非消耗性社会压力。
