Understanding patterns and processes in models of trophic cascades

Area of Science:

• Ecology
• Ecosystem Dynamics
• Food Web Theory

Background:

• Global changes in nutrient enrichment and apex predator declines are altering ecosystems.
• Trophic cascades significantly impact food webs, with varying strengths across ecosystems.
• Existing food chain models do not fully explain the variability in cascade strength.

Purpose of the Study:

• To investigate the necessary conditions for generating realistic trophic cascades in food web models.
• To determine the role of model formulation, specifically density dependence, in reproducing observed cascade effects.
• To test the applicability of findings from simple food chains to more complex marine food web models.

Main Methods:

• Development and analysis of simple food chain models incorporating density-dependent regulation.
• Mathematical modeling of consumer uptake and mortality rates.
• Application of conclusions to a complex marine food web model with varying nutrient inputs and harvesting rates.

Main Results:

• Inclusion of density-dependent regulation is essential for realistic top-down cascades.
• Realistic bottom-up cascades require density dependence, particularly mortality regulation (e.g., disease, intraguild predation).
• These findings hold true for both simple food chains and complex marine food web models.

Conclusions:

• Density dependence is a key factor in the strength and realism of trophic cascades.
• Model formulation significantly influences the accurate representation of ecosystem dynamics.
• Understanding these mechanisms is vital for predicting and managing ecosystem responses to environmental change.