A unifying theory for top-heavy ecosystem structure in the ocean

Area of Science:

• Ecology
• Marine Biology
• Ecosystem Dynamics

Background:

• Ecosystem structure is typically dictated by body size, with biomass decreasing at higher trophic levels.
• Inefficient energy transfer traditionally results in bottom-heavy ecological pyramids.

Purpose of the Study:

• To investigate how generalist predatory behavior and lower trophic feeding in large animals alter ecosystem biomass and structure.
• To determine if these behaviors can shift ecosystems from bottom-heavy pyramids to top-heavy hourglass structures.

Main Methods:

• The study theoretically models ecosystem structure based on body size and feeding strategies.
• It analyzes the impact of generalist predation and trophic level on biomass distribution.

Main Results:

• Generalist predatory behavior and feeding lower on the trophic web by large animals increase overall ecosystem biomass.
• These behaviors shift ecosystem structure from a bottom-heavy pyramid to a top-heavy hourglass, with large animals comprising the most biomass.
• These effects are predicted to be particularly significant in marine ecosystems.

Conclusions:

• Deviations from simple size-based predictions, such as generalist feeding in large animals, can fundamentally alter ecosystem biomass and structure.
• The findings offer a new framework for predicting and understanding ocean ecosystem structure historically and in the future without invasive methods.