Early View (EV): 1-EV A combination of functionally different plant traits provides a means to quantitatively predict a broad range of species assemblages in NW Europe J. C. Douma, R. Aerts, J. P. M. Witte, R. M. Bekker, D. Kunzmann, K. Metselaar and P. M. van Bodegom J. C. Douma (bob.douma@ecology.falw.vu.nl), R. Aerts, J. P. M. Witte and P. M. van Bodegom, Dept of Systems Ecology, Inst. of Ecological Science, VU Univ. Amsterdam, De Boelelaan 1085, NL-1081 HV Amsterdam, the Netherlands. JPMW also at: KWR Watercycle Research Inst., PO Box 1072, NL-3430 BB Nieuwegein, the Netherlands. – R. M. Bekker, Community and Conservation Ecology Group, Univ. of Groningen, PO Box 14, NL-9750 AA Haren, the Netherlands. – D. Kunzmann, Inst. of Landscape Ecology and Consulting, Lerchenstrasse 20, DE-26215 Wiefelstede, Germany. – K. Metselaar, WUR, Earth Sciences Group, Droevendaalsesteeg 4, NL-6708 PB Wageningen, the Netherlands. Assembly theory predicts that iltering processes will select species by their attributes to build a community. Some il- ters increase functional similarity among species, while others lead to dissimilarity. Assuming converging processes to be dominant within habitats, we tested in this study whether species assemblages across a wide range of habitats can be distinguished quantitatively by their mean trait compositions. In addition, we investigated how many and which traits are needed to describe the diferences between species assemblages best. he approach has been applied on a dataset that included 12 plant traits and 7644 vegetation relevés covering a wide range of habitats in the Netherlands. We demonstrate that due to the dominant role of converging processes 1) the functional composition can explain up to 80% of the loristic diferences between species assemblages using seven plant traits, showing that plant trait combinations provide a powerful tool for predicting the occurrence of species assemblages across diferent habitats; 2) to achieve a high performance, traits should be taken from diferent strategy components, i.e. traits that are functionally orthogonal, which does not necessarily coincide with low trait-trait correlations; 3) the diferent strategy components identiied in this study correspond to the strategy components of some conventional plant ecological strategy schemes (PESS) – schemes to describe the variation between individual species. However, some PESS merge traits into one strategy component that are shown to be function- ally diferent when predicting species assemblages. If such PESS is used to predict assemblages, this leads to a loss in predic- tive capacity. Potentially, our new approach is globally applicable to quantify community assembly patterns. However this needs to be tested. Plant species have various physiological and morphological adaptations to cope with the three most important challenges they face during their life cycle: how to disperse, how to establish and how to persist (Weiher et al. 1999). Although these challenges are common among all species, the range of biotic and abiotic conditions in which they can disperse, establish or persist difers between species. herefore it has been proposed that these abiotic and biotic conditions act as a ilter, retaining over time those species that have speciic combinations of traits that allow adaptation to the speciic local situation (Keddy 1992, Ordoñez et al. 2009, Elser et al. 2010). Generally it is argued that abiotic factors reduce the range of viable plant strategies, leading to a functional simi- larity of species within a habitat (trait convergence; Keddy 1992, Cornwell et al. 2006), while competition leads to competitive exclusion of functionally similar species and thus to trait divergence (Cornwell et al. 2006). Other biotic processes such as facilitation and mutualism can either have a diverging or a converging efect on traits (Valiente-Banuet and Verdu 2007, Sargent and Ackerly 2008). Several recent studies show that converging processes are dominant over diverging processes at the assemblage level, as species within assemblages were functionally more simi- lar than expected by random assembly from the trait pool (Cornwell et al. 2006, Kraft et al. 2008, de Bello et al. 2009). If, in any habitat, converging processes are dominant at the scale of species assemblages, loristic diferences among spe- cies assemblages of diferent habitats may be described by diferences in functional trait composition of the species assemblage, given that species are limited in trait plasticity (Ackerly and Cornwell 2007). his would allow predicting the occurrence of speciic species assemblages in diferent environments by their mean trait values. As species assemblages are subject to multiple environ- mental ilters acting on multiple traits, the average functional composition of a species assemblage can best be described by Ecography 000: 001–010, 2011 doi: 10.1111/j.1600-0587.2011.07068.x © 2011 he Authors. Journal compilation © 2011 Ecography Subject Editor: Janet Franklin. Accepted 4 May 2011