Top-Down Control of Primary Production in Atlantic Salt Marshes

最高?大西洋盐沼初级生产的下降控制理解消费者的相对重要性(上？向下的力量)和资源供应(底部？在控制自然群落的生产和分布模式方面的上作用力一直是群落生态学的基本问题之一。许多水生群落已被证明有强大的顶部？向下控制，而大多数由维管植物主导的系统被认为是由底部控制的？部队。盐沼通常被用作维管植物主导的生态系统的教科书范例，受土壤因素和资源供应的控制。在这里，我们提供的数据表明，蜗牛的放牧控制了西大西洋盐沼中主要的大型植物——互花米草的初级生产。这种蜗牛在从新泽西到墨西哥湾的沼泽中很常见，经常在与死亡和衰老植物相关的中等沼泽高度高密度地发现。虽然人们一直认为这些地区是垂死植物的斑块，吸引了蜗牛的食腐动物，但我们的数据表明，蜗牛的放牧可能会产生这些模式，因此这些沼泽可能处于顶部以下？控制。在本研究中，我们将检验沼泽蜗牛Littoraria可以施加top？对美国东南部沼泽互花米草初级生产的控制。特别地，我们检查了我们对乔治亚沼泽的初步结果的普遍性，其中沼泽是由底部控制的范式？向上作用力最初是在30多年前开发的。具体来说，我们建议研究以下假设，以阐明这些系统中食草动物控制的原因和后果。1)在哪里？东南沼泽地区是否发生过以蜗牛为食的下降控制？我们将测试这样一种假设，即蜗牛密度足以控制网草的生产，这种密度发生在幼虫产量高和捕食者避难所重合的沼泽景观上。2)顶端在哪里？东南沼泽可能通过吃蜗牛来控制下降吗？我们将检验这样一种假设，即在沼泽景观上任何可以保持高蜗牛密度的地方，食草动物都可以控制网麻草的生产。3)东南盐沼的网麻草产量高是营养级联的结果，在那里，蜗牛捕食者，包括螃蟹、鱼和海龟，限制了能够限制网麻草产量的食草蜗牛的密度。这项研究的结果可能会改变我们对北美最主要的海岸线生态系统之一的看法。如果这些沼泽是潜在的消费者控制，正如假设的那样，我们如何管理、恢复和思考这些社区的生态和进化将需要重新思考。

Top?Down Control of Primary Production in Atlantic Salt MarshesUnderstanding the relative importance of consumers (top?down forces) and resource supply (bottom?up forces) in controlling the production and distribution patterns in natural communities has long been one of the fundamental questions of community ecology. Many aquatic communities have been shown to have strong top?down control, while most systems dominated by vascular plants have been assumed to be controlled by bottom?up forces. Salt marshes are generally used as textbook examples of ecosystems dominated by vascular plants that are controlled by edaphic factors and resource supplies. Here we present data that suggests grazing by the snail Littoraria irrorata controls primary production of the dominant macrophyte in western Atlantic salt marshes, the cordgrass Spartina alterniflora. This snail is common in marshes from New Jersey to the Gulf of Mexico and often is found at high densities at intermediate marsh elevations associated with dying and senescing plants. While it has been assumed that these areas represent patches of dying plants that attract snail detritivores, our data suggest that snail grazing may generate these patterns and thus that these marshes are potentially under top?down control.In this study, we will examine the general hypothesis that the marsh snail Littoraria can exert top?down control over the primary production of Spartina alterniflora on marshes in the southeastern United States. In particular, we examine the generality of our preliminary results on Georgia marshes where the paradigm that marshes are controlled by bottom?up forces was originally developed over 30 years ago. Specifically, we propose to examine the following hypotheses to elucidate the causes and consequences of grazer control in these systems.1) Where does top?down control by snail grazing occur on southeastern marshes? We will test the hypothesis that snail densities sufficient to control cordgrass production occur where high larval delivery and predator refuges coincide across marsh landscapes.2) Where is top?down control by snail grazing possible in southeastern marshes? We will examine the hypothesis that grazer control of cordgrass production is possible anywhere on the marsh landscape that high snail densities can be maintained.3) The high production of cordgrass in southeastern salt marshes is the consequence of a trophic cascade, where snail predators, including crabs, fish and turtles, limit the densities of grazing snails that are capable of limiting cordgrass production.The results of this study may change the way we view one of the most dominant shoreline ecosystems in North America. If these marshes are potentially consumer controlled, as hypothesized, how we manage, restore and think about these communities ecologically and evolutionarily will need to be rethought.