Reciprocal subsidies between freshwater and terrestrial ecosystems structure consumer resource dynamics

Area of Science:

• Ecology
• Ecosystem Science
• Biogeochemistry

Background:

• Cross-ecosystem resource exchange, especially across the freshwater-land interface, is crucial for understanding ecosystem dynamics.
• Freshwater ecosystems often receive substantial external subsidies, potentially boosting secondary production compared to terrestrial systems.

Purpose of the Study:

• To quantify the magnitude and direction of resource subsidies across the freshwater-land interface.
• To assess the impact of these subsidies on recipient animal communities.

Main Methods:

• A meta-analytic approach was employed to synthesize data from multiple studies.
• Stable isotope analysis was used to infer the contribution of subsidies to animal carbon.

Main Results:

• Aquatic ecosystems receive significantly larger subsidies than terrestrial ecosystems.
• Despite magnitude differences, subsidy contribution to animal carbon did not differ between ecosystem types, likely due to varying subsidy quality.
• Allochthonous subsidies most significantly impacted primary consumers and predators.

Conclusions:

• Resource subsidy quality, not just quantity, is critical in determining its impact on food webs.
• External subsidies play a significant role in structuring food webs through both bottom-up and top-down effects.
• Future research should incorporate food web dynamics and indirect interactions to fully understand subsidy effects.