Data/code from: Long-term data reveal that grazer density mediates climatic stress in salt marshes

Understanding how climate and local stressors interact is paramount for predicting future ecosystem structure. The effects of stressors are often examined in small-scale and short-term field experiments, limiting understanding of the spatial and temporal generality of the findings. Using a 22-year observational dataset of plant and grazer abundance in a Southeastern US salt marsh, we analyzed how changes in drought and snail density combined to affect plant biomass. We found: (1) increased drought severity and higher snail density both correlated with lower plant biomass; (2) drought and snail effects interacted additively; and, (3) snail effects had a threshold, with additive top-down effects only occurring when snails were present at high densities. These results suggest that the emergence of multiple stressor effects can be density-dependent, and they validate short-term experimental evidence that consumers can exacerbate environmental stress. These findings have important implications for predicting future ecosystem structure and managing natural ecosystems. The data and code included here can be used to replicate all analyses and figures in our manuscript.厘清气候与本地胁迫因子的相互作用机制，对预测未来生态系统结构至关重要。现有研究多通过小型、短期的野外实验探究胁迫因子的影响，这导致我们对研究结果的空间与时间普适性认知不足。本研究依托美国东南部盐沼中长达22年的植物与植食者丰度观测数据集，分析了干旱胁迫与螺类密度的联合变化如何影响植物生物量。本研究得到如下结论：(1) 干旱胁迫加剧与螺类密度升高均与植物生物量降低呈显著相关；(2) 干旱与螺类的影响呈加性交互作用；(3) 螺类的影响存在阈值效应，仅当螺类密度较高时，才会出现加性自上而下调控效应。上述结果表明，多重胁迫因子影响的显现可能具有密度依赖性，同时验证了短期实验得出的结论：消费者可加剧环境胁迫。本研究结果对预测未来生态系统结构以及自然生态系统管理均具有重要指导意义。 本数据集附带的代码与原始数据可用于复现本文手稿中的所有分析与图表绘制。