Institut de Recherche pour le Développement, Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS, Université de Montpellier, Université Paul Valéry, Montpellier, EPHE, IRD, Montpellier, France
Department of Ecology and Evolutionary Biology, Cornell University, Corson Hall, Ithaca, NY, USA.
Proc Biol Sci. 2018 Aug 22;285(1885):20180983. doi: 10.1098/rspb.2018.0983.
Understanding the variation in species interactions along environmental stress gradients is crucial for making robust ecological predictions about community responses to changing environmental conditions. The facilitation-competition framework has provided a strong basis for predictions (e.g. the stress-gradient hypothesis, SGH), yet the mechanisms behind patterns in animal interactions on stress gradients are poorly explored in particular for mobile animals. Here, we proposed a conceptual framework modelling changes in facilitation costs and benefits along stress gradients and experimentally tested this framework by measuring fitness outcomes of benefactor-beneficiary interactions across resource quality levels. Three arthropod consumer models from a broad array of environmental conditions were used including aquatic detritivores, potato moths and rainforest carrion beetles. We detected a shift to more positive interactions at increasing levels of stress thereby supporting the application of the SGH to mobile animals. While most benefactors paid no significant cost of facilitation, an increase in potato moth beneficiary's growth at high resource stress triggered costs for benefactors. This study is the first to experimentally show that both costs and benefits function simultaneously on stress gradients for animals. The proposed conceptual framework could guide future studies examining species interaction outcomes for both animals and plants in an increasingly stressed world.
理解物种相互作用沿环境胁迫梯度的变化对于对群落对环境条件变化的反应做出稳健的生态预测至关重要。促进-竞争框架为预测提供了坚实的基础（例如，胁迫梯度假说，SGH），然而，关于动物在胁迫梯度上相互作用模式的机制在很大程度上尚未得到探索，特别是对于移动动物。在这里，我们提出了一个概念框架，该框架模拟了沿胁迫梯度促进成本和收益的变化，并通过测量不同资源质量水平下受益者-援助者相互作用的适应度结果来实验验证该框架。我们使用了广泛环境条件下的三种节肢动物消费者模型，包括水生碎屑食者、马铃薯蛾和雨林腐肉甲虫。我们发现，随着胁迫水平的增加，相互作用变得更加积极，从而支持将 SGH 应用于移动动物。虽然大多数援助者没有付出显著的促进成本，但在高资源胁迫下，马铃薯蛾受益体的生长增加引发了援助者的成本。这项研究首次实验表明，对于动物来说，成本和收益在胁迫梯度上同时起作用。所提出的概念框架可以指导未来的研究，在一个压力越来越大的世界中，同时研究动植物的种间相互作用结果。
