Understanding how climate and local stressors interact is paramount for predicting future ecosystem structure. The effects of multiple 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 grazer 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 augment environmental stress. These findings have important implications for predicting future ecosystem structure and managing natural ecosystems.

中文翻译：

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长期数据表明，食草动物密度介导盐沼的气候压力


了解气候和当地压力源如何相互作用对于预测未来的生态系统结构至关重要。通常在小规模和短期现场实验中检查多种压力源的影响，限制了对研究结果的空间和时间普遍性的理解。利用美国东南部盐沼植物和食草动物丰度 22 年的观测数据集，我们分析了干旱和食草动物密度的变化如何共同影响植物生物量。我们发现：（1）干旱严重程度增加和蜗牛密度增加均与植物生物量降低相关； (2)干旱和蜗牛效应交互作用相加； (3) 蜗牛效应有一个阈值，只有当蜗牛以高密度存在时，才会出现自上而下的附加效应。这些结果表明，多种压力效应的出现可能与密度有关，并且它们验证了消费者可以增加环境压力的短期实验证据。这些发现对于预测未来生态系统结构和管理自然生态系统具有重要意义。