Animal functional traits: Towards a trait-based ecology for whole ecosystems

1. Functional traits and associated trait-based concepts have driven rapid innovation in ecology over recent years, with most progress based on insights from plants. However, plants are almost entirely restricted to a single trophic level, and an over-reliance on plant traits therefore neglects the complexity and importance of biotic interactions across trophic levels. 2. The need to expand the focus of trait-based ecology to account for trophic complexity has led to an upsurge in attention on animal functional traits and the emergence of new concepts relevant to community ecology, macroecology and ecosystem science. Recent progress in the compilation of global trait datasets for some animal taxa has opened up new possibilities for testing ecological theory. 3. In this Special Focus, we explore how trait-based ecology can expand the scope of investigation from single to multiple trophic levels, how insights from these investigations can be used to upscale understanding from local communities to biogeographical patterns and how this can ultimately help to predict the impacts of global change on ecosystem functions. To address these key questions, we showcase studies on diverse animal taxa ranging in size from springtails to crocodiles and spanning multiple trophic levels from primary consumers to apex predators. 4. This collection of studies shows how precise measurements of morphological or physiological traits can increase mechanistic understanding of community assembly across trophic levels, particularly of the mechanisms underpinning large-scale biodiversity patterns. Furthermore, a clearer picture is emerging of systematic animal responses to environmental change that shape the trait composition of ecological communities and affect ecosystem functioning. 5. The articles in this volume highlight the need to move trait-based ecology beyond the limits of taxonomic boundaries. The integration of trait data and concepts across trophic levels opens up new possibilities for identifying general ecological mechanisms that shape patterns and processes operating at different scales. The identification of key functional traits and their interplay across trophic levels can underpin the development of a trait-based ecology for whole ecosystems, which could eventually enable predictions of the ecosystem-level consequences of biodiversity loss.