Geographic variation in patterns of nestedness among local stream fish assemblages in Virginia

Area of Science:

• Ecology
• Zoology
• Biogeography

Background:

• Nestedness of faunal assemblages is a complex phenomenon influenced by multiple factors across scales.
• Previous studies indicated stream-based nestedness in fish assemblages due to colonization or extinction.
• Environmental gradients, such as temperature, may also drive nestedness patterns.

Purpose of the Study:

• To investigate the relationship between spatial scale, environmental gradients, and nestedness of freshwater fish assemblages.
• To determine how region size and topographic relief influence nestedness patterns.
• To explore the role of biotic and abiotic factors in structuring regional fish distribution.

Main Methods:

• Examined freshwater fish assemblages across a spatial hierarchy of regions in Virginia.
• Defined regions including river drainages, physiographic provinces, and subdrainages.
• Analyzed hydrologic variability and faunal turnover to assess colonization/extinction dynamics.

Main Results:

• Nestedness was significantly stronger in smaller spatial extents and regions with greater topographic relief.
• No evidence found that inter-annual colonization/extinction dynamics explained elevational differences in nestedness.
• Results indicate nestedness is influenced by interactions between biotic and abiotic factors at regional scales.

Conclusions:

• Strongest nestedness patterns in fish assemblages occur in smaller regions with pronounced environmental gradients.
• Biotic and abiotic interactions are key drivers of regional-scale nestedness.
• Spatial scale and environmental heterogeneity significantly shape faunal assemblage structure.