Although species interactions are often assumed to be strongest at small spatial scales, they can interact with regional environmental factors to modify food web dynamics across biogeographic scales. The Eastern oyster (Crassostrea virginica) is a widespread foundational species of both ecological and economic importance. The oyster and its associated assemblage of fish and macroinvertebrates is an ideal system to investigate how regional differences in environmental variables influence trophic interactions and food web structure. We quantified multiple environmental factors, oyster reef properties, associated species and trophic guilds on intertidal oyster reefs in ten estuaries along 900 km of the southeastern United States. Geographical gradients in Fall water temperature and mean water depth likely influenced regional variation in oyster reef food web structure. Variation in the biomass of mud crabs, an intermediate predator, was mostly (84.1%) explained by reefs within each site, and did not differ substantially among regions; however, regional variation in the biomass of top predators and of juvenile oysters also contributed to biogeographic variation in food web structure. In particular, region explained almost half (40.2%) of the variation in biomass of predators of blue crab, a top predator that was prevalent only in the central region where water depth was greater. Field experiments revealed that oyster mortality due to predation was greatest in the central region, suggesting spatial variation in the importance of trophic cascades. However, high oyster recruitment in the middle region probably compensates for this enhanced predation, potentially explaining why relatively less variation (17.9%) in oyster cluster biomass was explained by region. Region also explained over half of the variation in biomass of mud crab predators (55.2%), with the southern region containing almost an order of magnitude more biomass than the other two regions. In this region, higher water temperatures in the fall corresponded with higher biomass of fish that consume mud crabs and juvenile and forage fish, whereas these intermediate predators had lower biomass than in the other two regions. Collectively, these results show how environmental gradients interact with trophic cascades to structure food webs associated with foundation species across biogeographic regions.

中文翻译：

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区域环境变化和当地物种相互作用影响牡蛎礁生物地理结构

虽然物种相互作用通常被认为在小空间尺度上最强，但它们可以与区域环境因素相互作用，从而改变生物地理尺度上的食物网动态。东方牡蛎（Crassostrea virginica）是一种广泛存在的基础物种，具有生态和经济重要性。牡蛎及其相关的鱼类和大型无脊椎动物组合是研究环境变量的区域差异如何影响营养相互作用和食物网结构的理想系统。我们量化了美国东南部 900 公里十个河口潮间带牡蛎礁上的多种环境因素、牡蛎礁特性、相关物种和营养类群。秋季水温和平均水深的地理梯度可能影响牡蛎礁食物网结构的区域变化。泥蟹是一种中间捕食者，其生物量的变化主要（84.1%）由每个地点的珊瑚礁解释，并且在区域之间没有显着差异；然而，顶级捕食者和幼牡蛎生物量的区域差异也导致了食物网结构的生物地理差异。特别是，区域解释了青蟹捕食者生物量变化的近一半（40.2%），青蟹是一种仅在水深较大的中部地区普遍存在的顶级捕食者。现场实验表明，由于捕食导致的牡蛎死亡率在中部地区最大，这表明营养级联重要性的空间变化。然而，中部地区牡蛎的大量补充可能弥补了这种增强的捕食行为，这可能解释了为什么牡蛎群生物量的变化相对较小（17.9%）是按地区来解释的。该地区还解释了泥蟹捕食者生物量变化的一半以上（55.2%），南部地区的生物量几乎比其他两个地区高一个数量级。在该地区，秋季较高的水温对应于消耗泥蟹、幼鱼和饲料鱼的鱼类生物量较高，而这些中间捕食者的生物量低于其他两个地区。总的来说，这些结果显示了环境梯度如何与营养级联相互作用以构建与跨生物地理区域的基础物种相关的食物网。