Top-Down Control of Primary Production in Atlantic Salt Marshes

托普？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（顶部？向下的力量）和资源供应（底部？自然群落中的生产和分布格局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，而大多数系统占主导地位的维管植物已被假定为控制底部？向上的力量盐沼通常被用来作为教科书的例子，生态系统占主导地位的维管植物是由土壤因素和资源供应。在这里，我们提出的数据表明，放牧的蜗牛Littoraria alphorata控制主要生产的大型植物在西大西洋盐沼，灯心草互花米草。这种蜗牛在从新泽西到墨西哥湾的沼泽中很常见，经常在与垂死和衰老植物有关的中间沼泽海拔高度以高密度被发现。虽然它已被假定，这些地区代表了垂死的植物，吸引蜗牛食草动物补丁，我们的数据表明，蜗牛放牧可能会产生这些模式，因此，这些沼泽地是潜在的下顶？向下控制。在这项研究中，我们将检查的一般假设，沼泽蜗牛Littoraria可以发挥顶部？美国东南部沼泽地互花米草初级生产的控制权。特别是，我们研究的一般性，我们的初步结果格鲁吉亚沼泽的范例，沼泽控制底部？UP FORCES最初是在30多年前开发的。具体而言，我们建议检查以下假设，以阐明原因和后果的食草动物控制在这些系统。1）在哪里？东南部的沼泽地会出现蜗牛放牧来控制羽绒的现象吗？我们将测试的假设，蜗牛密度足以控制大米草生产发生在高幼虫交付和捕食者避难所吻合整个沼泽湿地。2）顶部在哪里？在东南部的沼泽地，通过蜗牛放牧来控制下降是可能的吗？我们将研究这样一个假设，即在沼泽景观的任何地方，草食动物都可以控制大米草的产量，因为蜗牛密度很高。3）东南部盐沼大米草的高产是营养级联的结果，在那里，蜗牛的捕食者，包括螃蟹、鱼和海龟，限制放牧蜗牛的密度，这些蜗牛能够限制绳草的产量。这项研究的结果可能会改变我们对北方最主要的海岸线生态系统之一的看法。美国参考如果这些沼泽地是潜在的消费者控制，假设，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.