Local and collective transitions in sparsely-interacting ecological communities

Area of Science:

• Ecology
• Theoretical Ecology
• Network Theory

Background:

• Natural communities exhibit heterogeneous interactions, often modeled as sparse interaction networks.
• Understanding community structure is crucial for predicting ecological dynamics.

Purpose of the Study:

• To investigate the consequences of sparse competitive interactions in a theoretical community assembly model.
• To determine how interaction strength influences community structure and stability.

Main Methods:

• A theoretical model of community assembly from a species pool.
• Analysis of community structure across varying interaction strengths.

Main Results:

• Communities exhibit different regimes based on interaction strength: strong interactions lead to fragmented networks, while weaker interactions result in larger, more complex networks encompassing all species.
• Decreasing interaction strength drives the emergence of new allowed subgraphs, causing sharp changes in diversity and community properties.
• Two collective transitions occur at weaker interactions: a percolation transition and a transition between unique and multiple alternative equilibria.

Conclusions:

• Community structure is determined by allowed subgraphs at a given interaction strength and their arrangement across the community.
• Modifying interaction strength alone, without heterogeneity in interactions or species number, can traverse different community regimes.