Trait‐Based Functional Groups of Testate Amoebae: Classification and Ecological Implications

ABSTRACT Trait‐based approaches are increasingly used in ecology to better understand species' functional roles and adaptations. Testate amoebae, a diverse group of microbial eukaryotes driving important ecological functions, are particularly suited for trait‐based analysis due to their considerable morphological variability. However, traditional classifications of testate amoebae rely primarily on morphology, potentially overlooking ecologically relevant information. This study developed a novel system of functional groups for testate amoebae based on 18 functional traits and assessed its ecological significance. We used hierarchical clustering on a trait database encompassing 372 species from the Northern Holarctic realm. Our analysis identified seven distinct functional groups, which reflect adaptive strategies linked to shell size, aperture traits, and feeding modes: large‐bodied predators (Groups 1 and 2), medium‐sized bacterivores (Groups 3–5), patelliform generalists (Group 6), and small, highly adaptable taxa (Group 7). A case study in the Eastern European Plain revealed that organic soils harbored greater functional diversity, with species spanning all groups, while mineral soils were dominated by Group 5 (hemispheric, drought‐tolerant bacterivores). Functional space ordination highlighted habitat‐driven divergence, with organic soil communities characterized by traits optimizing resource exploitation (e.g., straight terminal apertures, idiosome shells) and mineral soils favoring desiccation‐resistant morphologies (central ventral apertures, compact shells). The new functional classification provides a more comprehensive understanding of the testate amoebae's ecological functions and improves our ability to predict their responses to environmental change.