DOI: 10.5061/dryad.612jm642j
title: Including intraspecific trait variability to avoid distortion of functional diversity and ecological inference: lessons from natural assemblages

description: 1. Functional diversity assessments are crucial and increasingly used for
 understanding ecological processes and managing ecosystems. The functional
 diversity of a community is assessed by sampling traits at one or more
 scales (individuals, populations, species) and calculating a summary index
 of the variation in trait values. However, it remains unclear how the
 scale at which traits are sampled and the indices used to estimate
 functional diversity may alter the patterns observed and inferences about
 ecological processes. 2. For 40 plant and 61 ant communities, we assess
 functional diversity using six methods – encompassing various mean-based
 and probabilistic methods – chosen to reflect common scenarios where
 different levels of detail are available in trait data. We test whether
 including trait variability at different scales (from individuals to
 species) alter functional diversity values calculated using volume-based
 and dissimilarity-based indices, Functional Richness (FRic) and Rao,
 respectively. We further test whether such effects alter the functional
 diversity patterns observed across communities and their relationships
 with environmental drivers such as abiotic gradients and occurrences of
 invasive species. 3. Intraspecific trait variability strongly determined
 FRic and Rao. Methods using only species’ mean trait values to calculate
 FRic (convex hulls) and Rao (Gower-based dissimilarity) distorted the
 patterns observed when intraspecific trait variability was considered.
 These distortions generated Type I and Type II errors for the effects of
 environmental factors structuring the plant and ant communities. 4. The
 high sensitivity of FRic to individuals with extreme trait values was
 revealed in comparisons of different probabilistic methods including
 among-individual and among-population trait variability in functional
 diversity. By contrast, values and ecological patterns in Rao were
 consistent among methods including different scales of intraspecific trait
 variability. 5. Decisions about where traits are sampled and how trait
 variability is included in functional diversity can drastically change the
 patterns observed and conclusions about ecological processes. We recommend
 sampling the traits of multiple individuals per species and capturing
 their intraspecific trait variability using probabilistic methods. We
 discuss how intraspecific trait variability can be reasonably estimated
 and included in functional diversity in the common circumstance where only
 limited trait data are available.
description: The dataset includes: Functional
 traits measurements for ants (described in Wong et al. 2020 Oikos, 129,
 585-597) Functional traits measurements for vascular
 plants (described in Carmona et al. 2015 Functional Ecology, 29,
 579-588) Community composition (sites x species
 matrices) both for plants and ants Environmental
 information associated to each site, both for plants (water availability)
 and ants (invasion status and percentage ground cover)
 Scripts to perform all analyses and figures contained in the
 paper