Jaime Uria‐Diez

Aims: Spatial environmental heterogeneity has been considered an important co‐existence mechanism because environmental variation enables different species to co‐occur. We predict that if functional differences are important for co‐existence, then both species and functional diversity should be positively related to environmental heterogeneity.Location: Thirty three dry calcareous grassland sites in Estonia.Methods: In each site, we established a transect (10.0 m × 0.1 m), consisting of 100 quadrats (10 cm × 10 cm). In each quadrat, we recorded species richness and composition, and measured soil depth, moisture and light availability. We collected data on eight traits from most of the species found across the sites. We calculated functional diversity (FD) at the quadrat scale, and compared the observed FD to that expected at random using two null models. The first null model used all the species that occurred in the transect in the randomizations to determine environmental filtering from the transect to the quadrat. The second null model restricted the species used in the randomizations to those species whose trait range was within the range of the observed values in the quadrat, to detect evidence for niche partitioning. Quadrat mean trait values and variability in functional composition were then related to small‐scale mean environmental conditions and heterogeneity, respectively.Results: We found convergent patterns in biomass, specific leaf area, specific root length and clonality compared to randomized communities that included all species occurring in the transect, and found divergence in height and leaf area using the range‐restricted null model. Hence, we found patterns consistent with environmental filtering and niche partitioning depending on the traits considered. Quadrat mean traits were significantly correlated with the measured environmental variables, with the main trend being a positive relationship between size‐related traits and soil resources, and a negative relationship between these traits and light availability. Trait variability in height, leaf area, leaf dry matter content, specific root length and clonality was positively related to soil depth heterogeneity. There was a trend for species richness to be negatively related to environmental heterogeneity.Conclusions: Co‐occurring species were more similar in several traits partly due to micro‐environmental filtering in response to variability in soil depth. While environmental heterogeneity increased trait variability, negative relationships with species richness were observed. Hence, niche partitioning does not appear to be important for the maintenance of high small‐scale species richness in these grasslands.

Questions: What are the prevailing types of intraspecific spatial distributions and interspecific association patterns at species and life stage levels of trees in a tropical rain forest? Which ecological processes could structure these patterns? Possible processes include dispersal limitation, self‐thinning, facilitation and competition between species and life stages.Location: A tropical broad‐leaved forest in north‐central Vietnam.Methods: We used univariate and bivariate pair‐correlation functions to investigate the spatial distribution and association patterns of 18 abundant tree species. To disentangle first‐ and second‐order effects, we used a scale separation approach with the heterogeneous Poisson process as null model.Results: (1) Sixteen of 18 species had aggregated patterns at various scales and regardless of their abundance. (2) Significant and aggregated patterns were found in 64% of all specific life stages. (3) At scales up to 15 m, 12.4% species pairs showed significant associations, among that 71% were spatial attractions, 5% were spatial repulsions and 24% were non‐essential interactions. (4) In different life stage associations, attractions (81%) predominated over repulsions (19%) at small scales of up to 15 m.Conclusions: Our findings provide evidence that dispersal limitation may regulate the spatial patterns of tree species. Moreover, positive spatial associations between tree species and life stages suggest the presence of species herd protection and/or facilitation in this forest stand, while the persistence of intraspecific aggregation through life stages suggests a very late onset or even absence of self‐thinning. Habitat heterogeneity plays an important role for species distribution patterns, and the spatial segregation occurs at a scale around 15 m in this forest.