Skewed weak and Pareto-tailed strong interactions accompany community diversity and complexity

TL;DR

This study reveals that ecological communities exhibit a skewed distribution of interaction strengths with many weak and few strong links, which correlates with community diversity and complexity.

Contribution

The paper uncovers the SWAPS distribution as a new interaction signature in ecological communities, linking it to community diversity and taxonomic constraints.

Findings

Interaction strengths follow skewed weak and Pareto-strong tails (SWAPS).

SWAPS distribution is taxon-specific and conserved within taxa.

Emergence of SWAPS correlates with increased community diversity and complexity.

Abstract

Ecological communities are often characterized by many weak and few strong interspecific interactions, yet their quantitative structure, generative basis, and links to community-level properties remain poorly understood. Using two empirical datasets of plant--animal networks, we show that both trophic and mutualistic interaction strengths distribute skewed weak and Pareto-strong tails (SWAPS), as quantified by positive skewness and extreme value theory, respectively. We further find that interaction strengths are taxon-specific and largely constrained within taxa. In community assembly simulations based on a generalized Lotka--Volterra model, this taxonomic conservatism, together with multiple interaction types beyond trophic and mutualistic ones, is required for the emergence of SWAPS distribution. Notably, SWAPS distribution emerges not only at the species level but also across lineages, and its emergence accompanies increases in community diversity and complexity. Together, these results identify SWAPS distribution as a previously unrecognized interaction signature of ecological communities and provide a new perspective on the organization of community-level properties.