Collaborative Research: BoCP-Design: US-Sao Paulo: The roles of stochasticity and spatial context in dynamics of functional diversity under global change

在理解、预测和应对全球变化影响的竞赛中，淡水生态系统面临的风险最大。然而，管理或减轻全球变化的影响需要三个要素：1)对生态系统如何运作的基本理解；2)一种估算气候变化如何转化为生态系统变化的方法；3)外推到未来气候情景的方法。这项研究包含了与河流生态系统有关的这些要素。先前的研究强调了流网络的物理结构对流功能的重要性。目前的项目扩展了这项工作，纳入了一个额外的元素：水生群落的规模。较小的物种群落由较小的种群组成。此外，这些小种群往往在重要的生命率上有更大的变化，比如出生、死亡和局部灭绝。最终，这种变异会转化为生态系统功能的变异。然而，相对于流网络的结构，社区的大小并不是随机的。更大的溪流提供了更多的栖息地，因此通常种群规模更大。本研究探讨群落规模与河流网络结构之间的关系如何影响河流生态系统的功能。最后，该项目将使用模型来推断这些调查的结果，以预测河流生态系统将如何应对未来的全球变化。该项目为研究生和本科阶段的生态学教育创造了独特的机会，包括来自代表性不足的群体，并允许学生参与到工作中固有的国际关系中。这项工作将明确地解决以下假设。首先，由于种群增长率和密度的温度依赖性差异，与温带河流相比，热带河流中形成群落的人口随机程度更高。其次，作为社区聚集驱动因素的人口随机性和环境选择之间的平衡取决于网络位置、社区规模和分散之间的相互作用。第三，热带河流中较高的随机群落组合和分散受限的源头导致了较高的功能组成变异性。为了了解不同气候条件下网络位置相互作用对群落规模的影响，我们将在河流网络的多个位置对居住和分散的大型无脊椎动物进行深入调查。这些调查将在美国和巴西同时进行。这种南北对比最终将允许对未来气候情景进行外推。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

In the race to understand, anticipate, and counter the effects of global change, no systems are more at-risk than freshwater ecosystems. However, managing or mitigating the effects of global change requires three elements: 1) a basic understanding of how an ecosystem functions; 2) a method for estimating how changes in climate can translate to changes in an ecosystem; and 3) a method for extrapolating to future climate scenarios. This research contains those elements with respect to stream ecosystems. Previous research has highlighted the importance of the physical structure of a stream network on a stream’s function. The current project extends that work to incorporate an additional element: the size of an aquatic community. Smaller communities of species are composed of smaller populations. Also, those small populations tend to have higher variation in important vital rates like births, deaths, and local extinctions. Ultimately, that variation can translate into variation in ecosystem functioning. However, the size of a community is not random with respect to the structure of stream networks. Larger streams provide more area for habitat, and thus generally larger population sizes. This research investigates how the relationship between community size and stream network structure affect the functioning of stream ecosystems. Finally, the project will use modeling to extrapolate the results of these investigations into predictions of how stream ecosystems will respond to future global change. This project creates unique opportunities for ecology education at the graduate and undergraduate levels, including from under-represented groups, and allows students to participate in the international relationships that are inherent in the work. This work will explicitly address the following hypotheses. First, owing to temperature-dependent differences in population growth rates and densities, the degree of demographic stochasticity in shaping community assembly is higher in tropical streams compared to temperate ones. Second, the balance between demographic stochasticity and environmental selection as drivers of community assembly depends on the interaction between network position, community size, and dispersal. Third, higher stochastic community assembly in tropical streams and dispersal-limited headwaters result in higher variability in functional composition. To understand how the community size by network position interaction functions in diverse climates, we will conduct intensive surveys of both resident and dispersing macroinvertebrates at multiple positions in a river network. These surveys will be performed in parallel in both the US and Brazil. This North versus South comparison will ultimately allow for extrapolation to future-climate scenarios.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.