Unravelling the Enigma of Soil Animal Diversity: An Integrated Perspective from Functional Traits to Evolutionary History

Ting-Wen Chen 

Why does a single square meter of forest soil harbour thousands of animal species? Fifty years after Jonathan M. Anderson raised this question, soil ecology still struggles with a fragmented view on the coexistence of species. Researchers often study taxonomy, functional traits, and phylogeny in isolation. Each approach adds insight but leaves gaps in the picture of soil biodiversity. In this paper, I propose a Community-Trait-Phylogenetic Ecology framework which links evolutionary and ecological views, and explains how soil animal communities form and persist. The framework combines three research fields: 1. Biogeography describes species composition across local, regional, and global scales. 2. Functional traits divided into α‑niche traits (resource use) and β‑niche traits (environmental tolerance), showing whether resource partitioning or filtering by environment drives community assembly. 3. Phylogeny shapes trait expression and defines the pool of species. Evidence from springtails (Collembola, Hexapoda) and oribatid mites (Oribatida, Acari) shows the value of this framework. Global data synthesis reveals a mismatch between density and diversity, which challenges traditional biogeographic predictions. Trait analyses show that environmental filtering occurs at global scales. At regional and local scales, cryptic species that diverged millions of years ago coexist with distinct habitat preferences. In addition, ancient and recent lineages coexist across elevations. Morphological and physiological traits usually follow phylogenetic constraints. In contrast, trophic traits show high flexibility, which allows closely related species to coexist. This integrative view shifts soil animal ecology from describing patterns to understanding the mechanisms responsible for them. It also supports predictions of community responses to climate change and land‑use change. Finally, it guides conservation strategies that protect trait, functional, and evolutionary diversity along with species richness.