Model Successfully Predicts Large River System Fish Diversity

While scientists have developed methods to predict aspects of fish diversity in specific river locations, a model to understand what factors may drive a comprehensive suite of fish biodiversity patterns in a large and complex system of rivers has been elusive.

Now a group of researchers, including University of Maryland ecologist William Fagan, reports success using a so-called "neutral model" to study fish diversity in the sprawling Mississippi-Missouri River System. Their study appears in the May 8 issue of Nature.

According to Nature , "That a simple model with a minimal set of parameters can capture the observed biodiversity patterns in complex landscapes suggests that effective monitoring of environmental change is possible, and could contribute to resource management and conservation strategies."

"The neutral model approach means that we do not need to have detailed knowledge about the competitive hierarchy or species interactions within a group of organisms to quantitatively reproduce a wide variety of biodiversity patterns in that system," said Fagan, co-principal investigator of the study. "This 'pattern oriented modeling,' in which we simultaneously reproduce a wide variety of empirical results using a single model fit, is a powerful approach for analyzing complex systems."

Controversial Method
Using the neutral model, in which all species are assumed to be functionally equivalent, to predict biodiversity has been controversial in ecology circles.

"Neutrality is a 'hot' topic in ecology, because it flies in the face of decades of detailed studies of how species interact among themselves on local scales," says Fagan. "The application of the neutral model to a complex, hierarchically structured spatial network like the Mississippi-Missouri River System is new.

"With a neutral model, we can suggest that a coarse assumption of equality is an excellent starting point for large scale investigations when little species-specific information is available."

M-M River System
The Mississippi-Missouri River System was a good study area, Fagan says, because it is the largest confluent drainage system covered by the NatureServe dataset.

"The fact that we can replicate key aspects of the spatial patterns of fish biodiversity from the Appalachians to the Rockies testifies to the robustness of this approach," said Fagan.

"One upshot from this work, still to be vetted in other systems, is the idea that some knowledge of the branching geometry of a river network, coupled with average runoff production, can provide crucial insights into the amount and spatial distribution of freshwater biodiversity and how that biodiversity may change as discharge patterns change."

Research Team
Co-principal investigator with Fagan was Ignacio Rodriguez-Iturbe of Princeton University . This study is one of several ongoing projects between the University of Maryland and Princeton, building on the theme that the geometry of river networks influences key aspects of biodiversity.

The Fagan lab helped develop the analytical approach of the study, which blends the U.S. Geological Survey geomorphic and hydrologic databases with a comprehensive dataset on fish biodiversity, and facilitated access to the fish biodiversity dataset.

Heather Lynch, a postdoctoral fellow in the Fagan lab, also worked on the study, along with lead author Rachata Muneepeerakul of Princeton and Enrico Bertuzzo and Andrea Rinaldo of the Universita di Padova, Italy .

The research was funded by a grant from the James S. McDonnell Foundation.

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