Journal of Vegetation Science 23 (2012) 176–186 Individual-based trait analyses reveal assembly patterns in tree sapling communities Marcos B. Carlucci, Helena Streit, Leandro D.S. Duarte & Vale ´ rio D. Pillar Keywords Araucaria angustifolia; Assembly rules; Biotic interactions; Campos grassland; Environmental filtering; Limiting similarity; Niche partitioning; Trait convergence; Trait divergence Abbreviations CL = presence of compound leaves; LA = mean leaf area; SLA = specific leaf area; SP = presence of spines; TCAP = trait-convergence assembly patterns; TDAP = trait-divergence assembly patterns; TLM = presence of toothed leaf margin; TR = presence of leaf trichomes Nomenclature The International Plant Names Index (2011). Received 26 May 2011 Accepted 2 August 2011 Co-ordinating Editor: Alicia Acosta Carlucci, M.B. (corresponding author, marcos.carlucci@gmail.com), Streit, H. (lennastreit@gmail.com), Duarte, L.D.S. (duarte.ldas@gmail.com) & Pillar, V.D. (vpillar@ufrgs.br): Programa de Po ´ s-Graduac ¸a ˜o em Ecologia, Universidade Federal do Rio Grande do Sul, Av Bento Gonc ¸ alves 9500, CP 15007, Porto Alegre, RS, 91501-970, Brazil Abstract Question: Are trait-convergence assembly patterns (TCAP) and/or trait- divergence assembly patterns (TDAP) of tree sapling communities related to microhabitat gradients in forest patches? If so, which traits are related to such patterns? What are the niche mechanisms potentially responsible for commu- nity assembly? Location: Grassland–forest mosaic in Serra do Sudeste region, southern Brazil (ca. 30.8°S, 53.1°W). Methods: We used individual-based trait information of 1132 tree saplings in 40 plots along gradients of canopy openness and grazing intensity in forest patches in southern Brazil. We used a trait-based approach, bypassing taxo- nomic identification, as a first assessment of sapling community assembly in forest patches. Results: Both TCAP and TDAP indicate niche mechanisms underlying assembly of tree sapling communities. Specific leaf area (SLA), mean leaf area (LA) and relative abundance of toothed leaf margin (TLM) maximized TCAP. SLA and TLM tended to increase under more closed canopies, whereas LA had higher val- ues at intermediate canopy openness. SLA and LA maximized TDAP and tended to vary more in more closed canopies, whereas SLA and presence of spines, which also maximized TDAP, showed higher variation under lower grazing intensity. Conclusion: The taxon-free approach was very useful to infer niche mecha- nisms of tree sapling assembly in forest patches. By adopting an individual-based trait approach, we assumed that both intra-specific and intra-population trait variability were relevant for revealing assembly patterns. We highlight that the use of individual-based trait data in a metacommunity framework is an excellent way to evaluate TCAP and TDAP at the metacommunity scale, since it takes into account the entire variation of traits throughout communities. Introduction Niche theory is based on two research programmes with distinct philosophies: the first evaluates to what extent members of the same community tend to exhibit similarity in their functional traits (environmental filtering), whereas the second emphasizes that differences in func- tional attributes of organisms enable their co-existence (limiting similarity). Basically, starting from a regional or local pool of species (Zobel 1997) having different types of traits, the action of environmental filters constrains the types and values of traits that will compose local communities (van der Valk 1981; Keddy & Weiher 1999). Considering that only organisms having similar traits will remain in a given site, environmental filtering causes trait- convergence assembly patterns (TCAP) (Weiher & Keddy 1995; Grime 2006; Funk et al. 2008). As a contrary force, competition is expected to cause trait-divergence assembly patterns (TDAP), since co-existing organisms having high similarity in ecological requirements are likely to face com- petitive exclusion (MacArthur & Levins 1967; Wilson 1999). As a consequence of the two opposing forces, local communities may exhibit both TCAP and TDAP (Grime 2006; Pillar et al. 2009). In synthesis, niche theories are Journal of Vegetation Science 176 Doi: 10.1111/j.1654-1103.2011.01339.x © 2011 International Association for Vegetation Science