The production and transfer of biomass through trophic relationships is a core ecosystem function. The movement of energy through the food web is mediated by organisms operating in their niche space. For generalists, the size of this niche space is inherently plastic and changes in response to available food sources. Therefore, this relationship between ecosystem productivity and niche size is an important determinant of ecosystem function. Competing theories about the nature of this relationship predict that as productivity increases niche size will either increase as species capitalize on a general increase in resource availability or decrease as it becomes viable to focus on preferred production channels. Here, we test these two competing theoretical frameworks using a novel approach to determine trophic niche size using stable isotope analysis and hypervolume metrics. Resource use is quantified in two generalist fish species at three productivity levels in a seagrass ecosystem. Niche size of both species was inversely related to seagrass productivity, consistent with the hypothesis that increasing productivity allows species to focus on a narrower diet. This pattern describes the relationship between ecosystem production and niche size and provides an empirical ecological explanation for the resource maximization behaviors commonly observed in nature.

中文翻译：

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营养生态位的大小和重叠程度随着生态系统生产力的提高而减小

通过营养关系生产和转移生物量是生态系统的核心功能。通过食物网的能量运动是由在其利基空间中运行的生物介导的。对于通才，此利基空间的大小本质上是可塑性的，并且会根据可用的食物来源而发生变化。因此，生态系统生产力与生态位大小之间的这种关系是生态系统功能的重要决定因素。关于这种关系的性质的竞争理论预测，随着生产力的提高，生态位的大小将随着物种利用资源的普遍增加而增加，或者随着专注于首选生产渠道而减少，生态位的大小将减少。这里，我们使用一种新颖的方法来测试这两个相互竞争的理论框架，从而使用稳定的同位素分析和超量度指标来确定营养位的大小。在海草生态系统中，在三种生产力水平上，对两种通才鱼物种的资源利用进行了量化。这两个物种的生态位大小与海草生产力成反比，这与提高生产力使物种专注于更窄饮食的假设相一致。这种模式描述了生态系统生产与生态位大小之间的关系，并为自然界中普遍观察到的资源最大化行为提供了经验性的生态解释。这两个物种的生态位大小与海草生产力成反比，这与提高生产力使物种专注于更窄饮食的假设相一致。这种模式描述了生态系统生产与生态位大小之间的关系，并为自然界中普遍观察到的资源最大化行为提供了经验性的生态解释。两种物种的生态位大小与海草生产力成反比，这与提高生产力使物种专注于更窄饮食的假设相一致。这种模式描述了生态系统生产与生态位大小之间的关系，并为自然界中普遍观察到的资源最大化行为提供了经验性的生态解释。