| NSF Org: |
DEB Division Of Environmental Biology |
| Recipient: |
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| Initial Amendment Date: | June 15, 2020 |
| Latest Amendment Date: | June 15, 2020 |
| Award Number: | 2015634 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Andrea Porras-Alfaro
aporrasa@nsf.gov (703)292-2944 DEB Division Of Environmental Biology BIO Directorate for Biological Sciences |
| Start Date: | October 1, 2020 |
| End Date: | September 30, 2024 (Estimated) |
| Total Intended Award Amount: | $387,505.00 |
| Total Awarded Amount to Date: | $387,505.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
1000 SPRING GARDEN ST GREENSBORO NC US 27412-5068 (336)334-5878 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1400 Spring Garden St. Greensboro NC US 27412-5013 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): |
Population & Community Ecology, Ecosystem Science |
| Primary Program Source: |
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| Program Reference Code(s): | |
| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.074 |
ABSTRACT
The origin of variation in food chain length - the number of feeding links from producers to apex consumers in a food web - has intrigued ecologists for decades. Understanding controls of food chain length is important because it influences energy flow through ecosystems and contaminant concentrations in top predators that humans often consume. The prevailing thought has held that food chain length is determined by the size of an ecosystem. Large ecosystems can provide greater amounts of basal resources, support larger population sizes of constituent species, and/or mitigate the impact of environmental changes. However, while ample empirical evidence for the ecosystem size hypothesis exists in spatially simple systems (e.g., oceanic islands and lakes), there is less clear support in more spatially complex systems, such as branching river networks. The mixed results for the ecosystem size hypothesis in spatially complex systems imply the existence of overlooked factors that control food chain length. The project will explore the role of ecosystem complexity that is emerging as a key factor in ecosystem dynamics. Specifically, researchers will focus on the branching complexity of river networks and investigate its importance in driving food chain length. The broader impacts of this project include the following components. First, researchers will participate in outreach events through formal partnerships with K-12 schools. Second, the project will provide research training opportunities for underrepresented minorities and a postdoctoral scientist. Lastly, researchers will distribute open-source software through online repositories to facilitate the application of research products.
The project will combine theoretical and empirical approaches to test the following hypotheses: (1) complex river networks, with greater levels of branching, support long food chains because having more branches (i.e., tributary systems) with distinct geological and/or climatic backgrounds may provide diverse habitats that buffer the impact of environmental fluctuations; (2) ecosystem size in rivers (watershed area) has weak effects on food chain length due to the context-dependent association between environmental heterogeneity and ecosystem size. Researchers will develop a series of mathematical models to generate predictions for the association between food chain length and branching complexity/ecosystem size. Theoretical predictions will be validated by meta-analyses of existing datasets of food chain length and environmental covariates across the globe. Overall, the project will provide important insights into how ecological communities are structured in spatially complex systems.
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.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
For decades, ecologists have been fascinated by what drives natural variation in food chain length, i.e., the number of feeding steps from producers to top predators in a food web. Understanding what governs food chain length is crucial, as it affects energy transfer within ecosystems and the buildup of contaminants in apex predators, many of which are consumed by humans. While many hypotheses have been developed, the dominant idea is that food chain length is primarily related to the size of an ecosystem (the ecosystem hypothesis). However, previous evaluations on FCL have lacked a robust framework for addressing the potential influence of spatial ecosystem complexity, a geometric characteristic distinct from ecosystem size. In this project, we used mathematical theory and meta-analysis to demonstrate that ecosystem complexity, rather than ecosystem size, plays a broader role in regulating food chains in rivers. Our theory predicted that the complex branching patterns of tributaries in river networks (ecosystem complexity) help buffer downstream areas from disturbances like floods, allowing longer food chains to persist. In contrast, the total size of a river system (ecosystem size, for example as represented by the total length of the river channel or other metrics) had no consistent impact on food chain length. A meta-analysis of global food chain data supported these theoretical findings: the complexity of river branching consistently had positive effects on riverine food chains worldwide, whereas the total river length showed no clear relationships. These findings challenge the prevailing view that larger ecosystems consistently support longer food chains. Instead, they reveal how the shape and complexity of an ecosystem influence its food web. This discovery provides a conceptual grounding for understanding the organization of food webs in ecosystems with complex spatial structures, improving our ability to design future conservation efforts.
This project has created meaningful broader impacts. Researchers engaged in outreach activities by collaborating with the regional science event at the University of North Carolina Greensboro, inspiring and educating the next generation of scientists. Additionally, the project provided research training opportunities to five undergraduate/graduate students and three postdoctoral scientists with diverse backgrounds, fostering diversity in science and supporting their professional development. To further extend its reach, the project distributed open-source R packages through online repositories, ensuring that the research products are widely accessible and easily applicable.
Last Modified: 01/26/2025
Modified by: Akira Terui
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