Summary 1.Trait-based approaches are increasingly being used to test mechanisms underlying species assemblages and biotic interactions across a wide range of organisms including terrestrial arthropods and to investigate consequences for ecosystem processes. Such an approach relies on the standardized measurement of functional traits that can be applied across taxa and regions. Currently, however, unified methods of trait measurements are lacking for terrestrial arthropods and related macroinvertebrates (terrestrial invertebrates hereafter). 2. Here, we present a comprehensive review and detailed protocol for a set of 29 traits known to be sensitive to global stressors and to affect ecosystem processes and services. We give recommendations how to measure these traits under standardized conditions across various terrestrial invertebrate taxonomic groups. 3. We provide considerations and approaches that apply to almost all traits described, such as the selection of species and individuals needed for the measurements, the importance of intraspecific trait variability, how many populations or communities to sample and over which spatial scales. 4. The approaches outlined here provide a means to improve the reliability and predictive power of functional traits to explain community assembly, species diversity patterns and ecosystem processes and services within and across taxa and trophic levels, allowing comparison of studies and running meta-analyses across regions and ecosystems. Ecology 2017Ecology , 31, 558-567 doi: 10.1111Ecology /1365Ecology -2435 5. This handbook is a crucial first step towards standardizing trait methodology across the most studied terrestrial invertebrate groups, and the protocols are aimed to balance general applicability and requirements for special cases or particular taxa. Therefore, we envision this handbook as a common platform to which researchers can further provide methodological input for additional special cases.

Functional ecology is the branch of ecology that focuses on various functions that species play in the community or ecosystem in which they occur. This accessible guide offers the main concepts and tools in trait-based ecology, and their tricks, covering different trophic levels and organism types. It is designed for students, researchers and practitioners who wish to get a handy synthesis of existing concepts, tools and trends in trait-based ecology, and wish to apply it to their own field of interest. Where relevant, exercises specifically designed to be run in R are included, along with accompanying on-line resources including solutions for exercises and R functions, and updates reflecting current developments in this fast-changing field. Based on more than a decade of teaching experience, the authors developed and improved the way theoretical aspects and analytical tools of trait-based ecology are introduced and explained to readers.

Predicted changes in soil water availability regimes with climate and land-use change will impact the community of functionally important soil organisms, such as macro-detritivores. Identifying and quantifying the functional traits that underlie interspecific differences in desiccation resistance will enhance our ability to predict both macro-detritivore community responses to changing water regimes and the consequences of the associated species shifts for organic matter turnover. Using path analysis, we tested (1) how interspecific differences in desiccation resistance among 22 northwestern European terrestrial isopod species could be explained by three underlying traits measured under standard laboratory conditions, namely, body ventral surface area, water loss rate and fatal water loss; (2) whether these relationships were robust to contrasting experimental conditions and to the phylogenetic relatedness effects being excluded; (3) whether desiccation resistance and hypothesized underlying traits could explain species distribution patterns in relation to site water availability. Water loss rate and (secondarily) fatal water loss together explained 90% of the interspecific variation in desiccation resistance. Our path model indicated that body surface area affects desiccation resistance only indirectly via changes in water loss rate. Our results also show that soil moisture determines isopod species distributions by filtering them according to traits underpinning desiccation resistance. These findings reveal that it is possible to use functional traits measured under standard conditions to predict soil biota responses to water availability in the field over broad spatial scales. Taken together, our results demonstrate an increasing need to generate mechanistic models to predict the effect of global changes on functionally important organisms.

Summary1. There is a growing consensus that the distribution of species trait values in a community can greatly determine ecosystem processes and services delivery. Two distinct components of community trait composition are hypothesized to chiefly affect ecosystem processes: (i) the average trait value of the species, quantified by community-weighted mean trait values (CWM; related to the mass ratio hypothesis) and (ii) the degree to which trait values differ between species in a community, quantified by different indices of functional diversity (FD; related to non-additive community effects). The uncertainty on the relative effect of these two components is stimulating an increasing number of empirical studies testing their effects on ecosystem processes and services delivery. 2. We suggest, however, that the interdependence between CWM and FD poses a challenge on disentangling their relative importance. We present a framework that allows designing experiments to decouple and assess the effects of these two community functional components on ecosystem processes and services. To illustrate the framework, we focused on leaf litter decomposition, as this is an essential process related to important ecosystem services. Using simulations, we applied the framework for plant leaf litter traits (litter nitrogen and phenolic content) that are related to litter decomposition. 3. CWM and FD generally showed a hump-shaped relationship (i.e. at more extreme CWM values, communities can have only low FD values). Within this relationship, we showed that it is possible to select quasi-orthogonal combinations of CWM and FD that can be treated statistically. Within these orthogonal CWM and FD combinations, it is also possible to select species assemblages controlling for other community parameters, such as total biomass, total density and species richness. 4. Synthesis. The framework provides a novel approach for designing experiments to decouple the effects of CWM and FD of communities on ecosystem processes, which otherwise cannot be easily disentangled. To apply the framework and design proper experimental layouts, it is essential to have a priori knowledge of the key traits by which species affect ecosystem processes and service delivery.

AimThe drivers of species assembly, by limiting the possible range of functional trait values, can lead to either convergent or divergent distributions of traits in realized assemblages. Here, to evaluate the strengths of these species assembly drivers, we partition trait variance across global, regional and community scales. We then test the hypothesis that, from global to community scales, the outcome of co-occurring trait convergence and divergence is highly variable across biomes and communities.Location Global: nine biomes ranging from subarctic highland to tropical rain forest. MethodsWe analysed functional trait diversity at progressively finer spatial scales using a global, balanced, hierarchically structured dataset from 9 biomes, 58 communities and 652 species. Analyses were based on two key leaf traits (foliar nitrogen content and specific leaf area) that are known to drive biogeochemical cycling.Results While 35% of the global variance in these traits was between biomes, only 15% was between communities within biomes and as much as 50% occurred within communities. Despite this relatively high within-community variance in trait values, we found that trait convergence dominated over divergence at both global and regional scales through comparisons of functional trait diversity in regional and community assemblages against random (null) models of species assembly. Main conclusionsWe demonstrate that the convergence of traits occurring from global to regional assemblages can be twice as strong as that from regional to community assemblages, and argue that large differences in the nature and strength of abiotic and biotic drivers of dominant species assembly can, at least partly, explain the variable outcome of simultaneous trait convergence and divergence across sites. Ultimately, these findings stress the urgent need to extend species assembly research to address those scales where trait variance is the highest, i.e. between biomes and within communities.

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1. It has long been recognized that leaf traits exert a crucial control on litter decomposition, a key process for nutrient cycling, and that invading species can greatly alter such soil processes via changes in mixed litter trait composition. Trait effects on ecosystem processes are hypothesized to operate via changes in either dominant trait values in the community (often calculated as community-weighted mean trait values; CWM) or trait functional diversity (dissimilarity between species trait values; FD). Few have studied the effects of these community trait components in tandem due to their interdependence. 2. We studied litter mixture decomposition using three exotic and six native European tree species with a range in litter decomposability, to disentangle the unique and combined roles of CWM and FD in explaining net litter mixture mass loss. 3. We showed that while CWM exerted the strongest effect on mass loss, FD modulated its effects, increasing mass loss in mixtures with low mean decomposability and decreasing mass loss in mixtures with high mean decomposability. Litter species identity and native/exotic status explained relatively little additional variation in mass loss after accounting for CWM and FD. We further showed that alterations to CWM and FD were more important than the replacement of a native species with an exotic counterpart in predicting mass loss. 4. Synthesis: Our results indicate that the effect of adding an exotic or losing a native species on litter decomposition rate can be predicted from how a species alters both CWM and FD trait values. This supports the idea that the repercussions of exotic species on ecosystem processes depends on the extent that introduced species bear novel traits or trait values and so on how functionally dissimilar a species is compared to the existing species in the community.

Traditionally, trait‐based studies have explored single‐trait‐fitness relationships. However, this approximation in the study of fitness components is often too simplistic, given that fitness is determined by the interplay of multiple traits, which could even lead to multiple functional strategies with comparable fitness (i.e. alternative designs). Here we suggest that an analytical framework using boosted regression trees (BRT) can prove more informative to test hypotheses on trait combinations compared to standard linear models. We use two published datasets for comparisons: a botanical garden dataset with 557 plant species (Herben, 2012, Journal of Ecology, 100, 1522) and an observational dataset with 83 plant species (Adler, 2014, Proceedings of the National Academy of Sciences, 111, 740). Using the observational dataset, we found that BRTs predict the role of traits on the relative importance of survival, growth and reproduction for population growth rate better than linear models do. Moreover, we split species cultivated in different habitats within the botanical garden and observed that seed and vegetative reproduction depended on trait combinations in most habitats. Our analyses suggest that, while not all traits impact fitness components to the same degree, it is crucial to consider traits that represent different ecological dimensions. Synthesis. The analysis of trait combinations, and corresponding alternative designs via BRTs, represent a promising approach for understanding and managing functional changes in vegetation composition through measurement of suites of relatively easily measurable traits.