Top-down control inhibits spatial self-organization of a patterned landscape

Area of Science:

• Ecology
• Marine Biology
• Ecosystem Dynamics

Background:

• Self-organized spatial patterns in primary producers are common but their formation is poorly understood.
• The role of consumers, particularly herbivores, in influencing these patterns has not been studied.

Purpose of the Study:

• To investigate the impact of herbivore grazing on the self-organized spatial patterns of diatom-covered hummocks in an intertidal mudflat ecosystem.
• To determine if top-down trophic control by herbivores influences the development and maintenance of these primary producer patterns.

Main Methods:

• Observational study of spatial patterns and herbivore populations over time on a Dutch intertidal mudflat.
• Manipulative field experiment involving the exclusion of benthic herbivores from designated sediment plots.
• Quantification of diatom growth, hummock formation, and sediment bed level variation in experimental and control plots.

Main Results:

• Regular spatial patterns of diatom hummocks formed in spring but collapsed by summer.
• A significant increase in benthic herbivore abundance coincided with pattern collapse.
• Herbivore exclusion experiments demonstrated that herbivores actively inhibit diatom growth and hummock formation.

Conclusions:

• Benthic herbivores exert top-down control on self-organized spatial patterns in primary producers.
• Herbivore activity is a key factor in the seasonal dynamics and collapse of these biological-geomorphic patterns.
• Understanding trophic interactions is crucial for predicting the resilience and functioning of intertidal ecosystems.