Burrowing animals can profoundly influence the structure of surrounding communities, as well as the performance of individual species. Changes in the community structure of burrowing animals or plants together with changing abiotic parameters could shift the influence of burrowers on surrounding habitats. For example, prior studies in salt marshes suggest that fiddler crabs stimulate cordgrass production, but leaf-grazing crabs suppress cordgrass production. Unfortunately, testing this prediction and others are impeded because few studies have examined crab impacts on the plant community and across multiple sites, multiple years, or both. This challenges our ability to predict how burrowing animals will influence plant community structure, and when and where these impacts will occur. We manipulated the densities of the dominant burrowing crabs in plant assemblages dominated by Pacific cordgrass (Spartina foliosa) and perennial pickleweed (Sarcocornia pacifica) at three sites in southern California for three years (2016, 2017, 2018). Crab impacts on plant community structure differed among each of our three sites. In contrast to our predictions, 1) leaf-grazing crabs (Pachygrapsus crassipes) had positive effects on cordgrass cover at one site and no effect on cordgrass production at a nearby site in the same marsh, and 2) fiddler crabs (Uca crenulata) did not stimulate cordgrass production at another marsh. Because crabs affected traits of cordgrass, but not pickleweed, in the direction consistent with changes in cordgrass cover, we propose that marsh-specific crab effects on community structure were largely mediated through changes in cordgrass, as opposed to pickleweed. Importantly, crabs facilitated cordgrass during marsh-wide cordgrass loss, suggesting that crabs may mitigate environmental stress for this ecologically important plant. Because cordgrass abundance can be a critical measure of marsh functioning and is often a restoration target, we suggest that managing cordgrass populations would benefit from additional information about crab populations and their impacts among years, and among and within marshes.

中文翻译：

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穴居蟹对植物群落结构影响的局部和区域差异

穴居动物可以深刻影响周围群落的结构，以及单个物种的表现。穴居动物或植物群落结构的变化以及非生物参数的变化可能会改变穴居动物对周围栖息地的影响。例如，先前在盐沼中进行的研究表明，招潮蟹会刺激禾本科植物的生产，但食叶蟹会抑制禾本科植物的生产。不幸的是，测试这一预测和其他预测受到阻碍，因为很少有研究检查螃蟹对植物群落和跨多个地点、多年或两者的影响。这挑战了我们预测穴居动物将如何影响植物群落结构以及这些影响将在何时何地发生的能力。我们在加利福尼亚南部的三个地点对以太平洋草（Spartina foliosa）和多年生泡菜（Sarcocornia pacifica）为主的植物组合中的主要穴居蟹的密度进行了三年（2016年、2017年、2018年）。螃蟹对植物群落结构的影响在我们三个地点中的每一个中都不同。与我们的预测相反，1) 食叶蟹 (Pachygrapsus crassipes) 对同一沼泽中一个地点的草履虫覆盖有积极影响，而对同一沼泽附近地点的草履虫产量没有影响，2) 招潮蟹 (Uca crenulata)不刺激另一个沼泽地的禾本科植物生产。因为螃蟹影响了草的性状，而不是泡菜，所以在与草覆盖变化一致的方向上，我们认为沼泽特有的螃蟹对群落结构的影响主要是通过禾本科植物的变化来调节的，而不是酸菜。重要的是，在整个沼泽地的禾本科植物损失期间，螃蟹促进了禾本科植物的生长，这表明螃蟹可以减轻这种具有重要生态意义的植物的环境压力。由于禾草丰度可以是沼泽功能的关键衡量标准，并且通常是恢复目标，因此我们建议管理禾草种群将受益于有关螃蟹种群及其在多年间以及沼泽之间和沼泽内的影响的额外信息。