title: Evaluating Functional Diversity: Missing Trait Data and the Importance of Species Abundance Structure and Data Transformation.
abstract: Functional diversity (FD) is an important component of biodiversity that quantifies the difference in functional traits between organisms. However, FD studies are often limited by the availability of trait data and FD indices are sensitive to data gaps. The distribution of species abundance and trait data, and its transformation, may further affect the accuracy of indices when data is incomplete. Using an existing approach, we simulated the effects of missing trait data by gradually removing data from a plant, an ant and a bird community dataset (12, 59, and 8 plots containing 62, 297 and 238 species respectively). We ranked plots by FD values calculated from full datasets and then from our increasingly incomplete datasets and compared the ranking between the original and virtually reduced datasets to assess the accuracy of FD indices when used on datasets with increasingly missing data. Finally, we tested the accuracy of FD indices with and without data transformation, and the effect of missing trait data per plot or per the whole pool of species. FD indices became less accurate as the amount of missing data increased, with the loss of accuracy depending on the index. But, where transformation improved the normality of the trait data, FD values from incomplete datasets were more accurate than before transformation. The distribution of data and its transformation are therefore as important as data completeness and can even mitigate the effect of missing data. Since the effect of missing trait values pool-wise or plot-wise depends on the data distribution, the method should be decided case by case. Data distribution and data transformation should be given more careful consideration when designing, analysing and interpreting FD studies, especially where trait data are missing. To this end, we provide the R package "traitor" to facilitate assessments of missing trait data.
authors.affiliation: Department of Soil Science, Faculty of Natural Sciences, Comenius University, Bratislava, Slovak Republic.|Department of Botany, Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic.
authors.forename: Maria
authors.initials: M
authors.lastname: Májeková
authors.affiliation: Institute of Ecology and Earth Sciences, University of Tartu, Tartu, Estonia.
authors.forename: Taavi
authors.initials: T
authors.lastname: Paal
authors.affiliation: Institute of Entomology, Biology Centre CAS, České Budějovice, Czech Republic.|Department of Zoology, Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic.
authors.forename: Nichola S
authors.initials: NS
authors.lastname: Plowman
authors.affiliation: Institute of Soil Biology, Biology Centre CAS, České Budějovice, Czech Republic.|Department of Ecosystem Biology, Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic.
authors.forename: Michala
authors.initials: M
authors.lastname: Bryndová
authors.affiliation: Institute of Ecology and Earth Sciences, University of Tartu, Tartu, Estonia.
authors.forename: Liis
authors.initials: L
authors.lastname: Kasari
authors.affiliation: Department of Biosciences, University of Helsinki, Helsinki, Finland.
authors.forename: Anna
authors.initials: A
authors.lastname: Norberg
authors.affiliation: Institute of Entomology, Biology Centre CAS, České Budějovice, Czech Republic.
authors.forename: Matthias
authors.initials: M
authors.lastname: Weiss
authors.affiliation: Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool, United Kingdom.|Centre for Invasion Biology, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa.
authors.forename: Tom R
authors.initials: TR
authors.lastname: Bishop
authors.affiliation: School of Biological Sciences, University of East Anglia, Norwich, United Kingdom.|Department of Zoology, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Sarah H
authors.initials: SH
authors.lastname: Luke
authors.affiliation: Institute of Entomology, Biology Centre CAS, České Budějovice, Czech Republic.|Department of Zoology, Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic.
authors.forename: Katerina
authors.initials: K
authors.lastname: Sam
authors.affiliation: Department of Botany, Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic.|Area de Biodiversidad y Conservación, Departamento de Ciencias, Escuela Superior de Ciencias Experimentales y Tecnología, Universidad Rey Juan Carlos, C/ Tulipán s/n, Móstoles, Spain.
authors.forename: Yoann
authors.initials: Y
authors.lastname: Le Bagousse-Pinguet
authors.affiliation: Department of Botany, Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic.|Institute of Entomology, Biology Centre CAS, České Budějovice, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Lepš
authors.affiliation: Institute of Botany, Biology Centre CAS, Třeboň, Czech Republic.
authors.forename: Lars
authors.initials: L
authors.lastname: Götzenberger
authors.affiliation: Department of Botany, Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic.|Institute of Botany, Biology Centre CAS, Třeboň, Czech Republic.
authors.forename: Francesco
authors.initials: F
authors.lastname: de Bello
mesh_terms: D044822:Biodiversity; D019655:Quantitative Trait, Heritable; D013045:Species Specificity