Geometric ecosystem complexity regulates food chains

Since Charles Elton's time, ecologists have been intrigued by the variation in food chain length across natural communities. A widely held belief is that the size of an ecosystem significantly influences food chain length, known as the ecosystem size hypothesis. However, discussions around food webs have often overlooked the potential role of spatial ecosystem complexity—a geometric feature that operates independently of ecosystem size. In this study, we combine theoretical modeling and meta-analysis to show that ecosystem complexity, rather than size, is a key factor in regulating food chains in rivers. Our spatial theory suggests that the intricate branching of tributaries helps to buffer downstream areas from disturbances like floods, thus supporting longer food chains. However, our theory suggests a vague relationship between food chain length and ecosystem size (measured as the total river length within a watershed), a prediction that contrasts sharply with the ecosystem size hypothesis. A meta-analysis of global food chain data strongly confirmed these theoretical insights. The complexity of river networks consistently had a positive impact on riverine food chains worldwide, while the total river length showed no consistent relationship. This study offers a conceptual framework for understanding the structure of food webs in ecosystems with complex spatial configurations.

Presentation Preference: Oral

Primary Presenter: Akira Terui, University of Tokyo (hanabi0111@gmail.com)

Authors:

Akira Terui, University of North Carolina at Greensboro  (hanabi0111@gmail.com)

Shota Shibasaki, National Institute of Genetics  (hanabi0111@gmail.com)

Justin Pomeranz, Colorado Mesa University  (jfpomeranz@gmail.com)

Mason Ibrahim, Duke University  (mni12202000@gmail.com)

Ethan Isaac, University of North Carolina at Greensboro  (eiisaac@uncg.edu)

Ashley LaRoque, University of North Carolina at Greensboro  (aalaroque@uncg.edu)

Dai Yamazaki, The University of Tokyo  (yamadai@rainbow.iis.u-tokyo.ac.jp)

Jacques Finlay, University of Minnesota  (jfinlay@umn.edu)