Linking plant and insect traits to understand multitrophic community structure in arid steppes

Summary 1. Animal ecology could benefit from a well-defined trait-based framework, mostly applied in plant ecology, to further develop predictions of animal communities under various environmental conditions. We extended the functional approach to a multitrophic system by combining plant and ant traits in relation to environmental conditions to study the relationships between these three components. 2. We sampled plant and ant abundances along an aridity gradient in grazed and ungrazed conditions in the arid steppes of eastern Morocco. We measured five plant functional traits related to water stress and grazing resistance and six ant functional traits related to body size, dispersal and behaviour. We related each component (environment, vegetation and ants) using Mantel partial correlations to uncover the causal structure between components and using a fourthcorner analysis to describe the effects of the environment and vegetation on ant communities. 3. Results indicated that vegetation had a direct effect on ant community composition while the environment only had an indirect effect on ant community composition through vegetation structure. This result was consistent when looking at both the taxonomic and functional composition of communities, but correlations were stronger when based on taxonomic composition. Aridity was the variable most significantly linked with ant functional traits 4. Synthesis. The use of functional traits in animal ecology is relatively new, and an increase in trait-based community ecology studies that include more than one trophic level would be beneficial in identifying trait-based patterns in multitrophic communities. This new approach could become very useful in identifying mechanistic explanations of multitrophic community assembly and making predictions about their evolution under changing environmental conditions. It could also be of practical use in conservation biology in assessing habitat quality.