Data from: Trophic niche size and overlap decreases with increasing ecosystem productivity

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.

通过营养关系实现的生物量生产与传递，是核心生态系统功能之一。能量经由食物网的流动，由占据其生态位空间的生物所介导。对于广食性物种而言，其生态位空间的大小本质上具有可塑性，并会随可获取食物资源的变化而发生改变。因此，生态系统生产力与生态位大小之间的这种关联，是决定生态系统功能的关键因素。针对这一关联的本质，存在两种竞争性理论预测：随着生产力提升，生态位大小要么因物种可利用的资源总量普遍增加而扩大，要么因聚焦于偏好的资源利用渠道变得可行而缩小。本研究采用基于稳定同位素分析与超体积（hypervolume）指标的创新方法来测定营养生态位大小，以此检验这两种竞争性理论框架。研究者在海草生态系统的三个生产力水平下，对两种广食性鱼类的资源利用情况进行了量化分析。结果显示，两种鱼类的生态位大小均与海草生产力呈负相关，这与“生产力提升可促使物种聚焦于更狭窄的食谱”的假说相符。该模式阐明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测到的资源最大化行为提供了经验性生态学解释。