COS 145-5 - Emergent dual scaling of biodiversity in rivers

Wednesday, August 9, 2023

9:00 AM – 9:15 AM PDT

Location: B119

Presenting Author(s)

AT

Akira Terui

Assistant Professor
University of North Carolina at Greensboro
Greensboro, United States

Coauthor(s)

SK

Seoghyun Kim

University of Tennessee Knoxville, United States
CD

Christine Dolph

University of Minnesota, United States
TK

Taku Kadoya

National Institute of Environmental Studies, Japan
YM

Yusuke Miyazaki

Kindai University, Japan

Abstract: A prevailing paradigm suggests that ecosystem size (or area) dictates a diverse array of biodiversity patterns, including metapopulation stability, species richness (the species-area relationship), and food chain length (the ecosystem size hypothesis). These ubiquitous relationships have formed the foundation of many conservation strategies. In spatially complex ecosystems, however, the ecosystem size may not be the sole dimension to scale biodiversity

patterns because the scale-invariant complexity of fractal ecosystem structure may drive ecological dynamics in space. Rivers exemplify such complex ecosystems with fractal branching structures.

Here, we used theory and analysis of extensive fish community data to show that riverine biodiversity follows a robust scaling law along the two orthogonal dimensions of ecosystem size and complexity (i.e., the dual scaling law). In river networks, the recurrent merging of various tributaries forms fractal branching systems, where the prevalence of branching (ecosystem complexity) represents a macroscale control of the ecosystem’s habitat heterogeneity. In the meantime, ecosystem size dictates metacommunity size and total habitat diversity. Our theory predicted that larger and more branched “complex” networks support greater species richness due to increased space and environmental heterogeneity. The relationships were linear on logarithmic axes, indicating power law scaling by ecosystem size and complexity. In support of this theoretical prediction, the power laws have consistently emerged in riverine fish communities across distinct geographic regions (Hokkaido Island in Japan and the midwestern United States) despite hosting different fauna with distinct evolutionary histories.

The emergence of dual scaling law may be a pervasive property of branching networks with important implications for biodiversity conservation. While our work is limited to the horizontal biodiversity (species richness), the prevailing impact of branching complexity may be extended to the vertical dimension of biodiversity (i.e., food chain length); indeed, our spatially explicit simulations predicted a dual control of food chain length by ecosystem size and complexity in rivers. Further empirical studies are required to generalize our framework to other dimensions of biodiversity.