When Do Trait-Based Higher Order Interactions and Individual Variation Promote Robust Species Coexistence?

Area of Science:

• Ecology
• Evolutionary Biology
• Theoretical Ecology

Background:

• Ecological models often simplify interactions to pairwise competition.
• Higher-order interactions (HOIs), where a third species affects a pairwise interaction, are increasingly recognized but their structure is poorly understood.
• HOIs could be mediated by species traits, potentially creating structured interaction patterns.

Purpose of the Study:

• To investigate the impact of trait-mediated higher-order interactions (HOIs) on species diversity, community structure, and coexistence.
• To compare models of competition alleviated by trait distance versus hierarchical competition.
• To analyze the role of individual variation and trait-based HOIs in community dynamics.

Main Methods:

• Developed models incorporating both pairwise and trait-mediated HOIs.
• Considered two classes of HOIs: trait distance-dependent competition and hierarchical competition.
• Integrated evolutionary dynamics using quantitative genetics.
• Analyzed the impact on species diversity, community patterns, and robustness of coexistence.

Main Results:

• Trait-mediated HOIs generally hinder, rather than promote, species coexistence, with exceptions noted.
• Communities structured by competitive trait hierarchies are vulnerable to perturbations, irrespective of HOIs.
• Trait-based HOIs with distance-dependent competition yield the most robust communities, with less impact from individual variation.
• Both individual variation and HOIs lead to a more even distribution of species traits.

Conclusions:

• Trait-mediated HOIs promote coexistence only under specific conditions.
• The effective interaction kernel, shaped by pairwise and HOI terms, predicts community outcomes.
• Future research should explore if multi-trait HOIs are necessary to positively influence coexistence in competitive communities.