Trait concepts, categories, and databases in soil invertebrates ecology – ordering the mess

The trait-based approach is increasingly used for soil invertebrates. Complementary to the taxonomy based approach, the trait-based approach can provide a more mechanistic understanding of the responses of organisms to environmental disturbances and of their effects on soil functioning. However, the application of the trait-based approach across studies is limited by the lack of conceptual consensus among researchers due to the historical development of the idea. There is a large ambiguity and variability in using the term ‘functional traits’ by zoologists and ecologists working on soil invertebrates. In this study, we used a questionnaire and literature scanning to review the practical use of functional traits concept in soil ecology over the last decade. We clarified and expanded the functional trait definition as ‘A functional trait is a measurable characteristic of an individual organism or its colony that has a link to the organism‘s fitness and/or its effect on other organisms and/or the environment’. We also reviewed existing trait databases showing a high amount, but also high heterogeneity and low accessibility of data on the functional traits of soil invertebrates. We suggest synthesising existing trait data and databases, using the functional trait-based approach consistently and reproducibly, and disseminating it to facilitate research in soil ecology.