Cross-ecosystem bottlenecks alter reciprocal subsidies within meta-ecosystems

Area of Science:

• Ecology
• Ecosystem Dynamics
• Meta-ecosystem Studies

Background:

• Ecosystems are linked by reciprocal subsidies, but energy transfer can be limited by organisms that do not cross ecosystem boundaries.
• Understanding how different subsidy types and predator presence affect energy flow is crucial for meta-ecosystem functioning.

Purpose of the Study:

• To investigate the influence of terrestrial insect and leaf subsidies on reciprocal energy flows in freshwater pond mesocosms.
• To determine the role of top predators in mediating these cross-ecosystem energy transfers.

Main Methods:

• A 2x2x2 factorial experiment was conducted over 18 months using freshwater pond mesocosms.
• Treatments included the addition of terrestrial insect larvae and willow leaves, with and without the presence of predatory fish (upland bullies).
• Reciprocal energy flow was measured by the emergence of aquatic insects.

Main Results:

• Terrestrial insect subsidies significantly increased reciprocal energy flow, indicated by higher aquatic insect emergence.
• Leaf subsidies had a dampening effect on reciprocal energy flow.
• The presence of fish and snails created a bottleneck, retaining energy within the aquatic ecosystem and limiting cross-ecosystem subsidy transfer.

Conclusions:

• The type of subsidy (insects vs. leaves) critically affects reciprocal energy flow in meta-ecosystems.
• Consumers without terrestrial life stages can act as bottlenecks, impeding energy transfer across ecosystem boundaries.
• Altering species composition in donor or recipient food webs can significantly modify reciprocal subsidies.