Abstract: Classifying species by shared life-history traits is important if common ecological response groups are to be identified among different species. We investigated how habitat area, local and regional factors shape plant communities in small isolated closed depressions, and how the species richness is related to the interplay between environmental factors and specific life-history trait combinations. In Central-Western Europe, 169 closed depressions were completely Surveyed for plant presence in two highly contrasted landscapes (forested and open landscapes). All species were clustered into 9 Emergent Groups based oil 10 life-history traits related to plant dispersal, establishment and persistence. Habitat areas were related to species presence using logistic regressions. Most Emergent Groups were more area-dependent in open than in forested landscapes, owing to heterogeneous light levels in forest weakening the species-area relationship. In open landscapes, Floating Hydrophytes were severely underrepresented in very small depressions, owing to the absence of waterfowl poulation. Local environmental and regional factors were related to species richness using Generalized Linear Models. In open landscapes, local environmental factors such as water conductivity or soil productivity are respectively the main predictors. In forested landscapes, the abundance of most Emergent Groups Was better predicted by regional factors, i.e., habitat connectivity and distance to the forest edge. Forested landscapes strongly impeded the closed depressions' colonization by the less mobile Emergent Groups Such as Large-seeded Perennials. (C) 2009 Elsevier Masson SAS. All rights reserved.

Abstract: In the understory of pristine Guianese forests, the myrmecophyte Hirtella physophora almost exclusively shelters colonies of the plant-ant Allomerus decemarticulatus in its leaf pouches. We experimentally tested three non-mutually exclusive hypotheses concerning phenomena that can determine the species specificity of this association throughout the foundation stage of the colonies: (1) interspecific competition results in the overwhelming presence of A. decemarticulatus queens or incipient colonies; (2) exclusion filters prevent other ant species from entering the leaf pouches; and (3) host-recognition influences the choice of founding queens, especially A. decemarticulatus. Neither interspecific competition, nor the purported exclusion filters that we examined play a major role in maintaining the specificity of this association. Unexpectedly, the plant trichomes lining the domatia appear to serve as construction material during claustral foundation rather than as a filter. Finally, A. decemarticulatus queens are able to identify their host plant from a distance through chemical and/or visual cues, which is rarely demonstrated in studies on obligatory ant-plant associations. We discuss the possibility that this specific host-recognition ability could participate in shaping a compartmentalized plant-ant community where direct competition between ant symbionts is limited. (C) 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 90-97.

Abstract: Though it is recognized that both stochastic and deterministic processes structure all communities, empirical assessments of their relative importance are rare, particularly within any single community. In this paper, we quantify the dynamic effects of dispersal assembly and niche assembly on the seedling layer in a diverse neotropical rain forest. The two theories make divergent predictions regarding the roles of seed arrival and environmental heterogeneity in generating community structure. Put simply, dispersal assembly posits that the stochasticity inherent to seed arrival structures communities, whereas niche assembly suggests that heterogeneity in post-dispersal environmental conditions is more important. We experimentally sowed 15,132 seeds of eight tree species at varying levels of density and diversity. Every six months we censused the seedlings that germinated and assessed the abiotic and biotic conditions of each plot. We assessed the density, diversity, and species composition of three nested subsets of the seedling layer: seedlings germinated from sown seeds, all seedlings germinated between July 2003 and 2004, and all woody seedlings. We partitioned the variance in density and diversity of each subset of the seedling layer into components representing seed-addition treatments and environmental conditions at 6- to 12-month intervals. Seed additions initially explained more variance in the density and diversity than did environmental heterogeneity for seven of eight sown species, but explained little variance in the density or diversity of the entire seedling layer. Species composition was better explained by seed-addition treatments than by environmental heterogeneity for all three subsets and in all time periods. Nevertheless, the variance in community structure explained by seed-addition treatments declined over the two years following germination, presaging shifts in the relative importance of dispersal assembly and niche assembly. Our study quantifies how dispersal assembly and niche assembly may vary among the components of an ecological community and shift dynamically through time.

Abstract: Diversity is positively correlated with water availability at global, continental and regional scales. With the objective of better understanding the mechanisms that drive these relationships. we investigated the degree to which variation in water availability affects the performance (recruitment, growth a rid survival) of juvenile trees. Precipitation was supplemented throughout two dry seasons in a seasonal moist forest in south-eastern Peru. Supplementing precipitation by 160 mm mo(-1), we increased soil moisture by 17%. To generate seedling communities or known species composition, we sowed 3840 seeds of 12 species. We monitored the fates of the 554 seedlings recruited from the sown seeds. as well as 1856 older non-sown seedlings (10 cm <= height < 50 cm), and 2353 saplings (> 1 m tall). Watering significantly enhanced young seedling growth and survival, increasing stern density and diversity. Watering diminished the recruitment of species associated with upland forests, but increased the survival of both upland- and lowland-associated species. Though supplemental watering increased the growth of older seedlings. their density and diversity were unaffected. Sapling performance was insensitive to watering. We infer that variation in dry-season water availability may affect seedling community structure by differentially affecting recruitment and increasing overall survival. These results suggest that differential seedling recruitment and survival may contribute to the observed relationships between water availability, habitat associations and patterns of tree species richness.

Abstract: Land use and climate changes induce shifts in plant functional diversity and community structure, thereby modifying ecosystem processes. This is particularly true for litter decomposition, an essential process in the biogeochemical cycles of carbon and nutrients. In this study, we asked whether changes in functional traits of living leaves in response to changes in land use and climate were related to rates of litter potential decomposition, hereafter denoted litter decomposability, across a range of 10 contrasting sites. To disentangle the different control factors on litter decomposition, we conducted a microcosm experiment to determine the decomposability under standard conditions of litters collected in herbaceous communities from Europe and Israel. We tested how environmental factors ( disturbance and climate) affected functional traits of living leaves and how these traits then modified litter quality and subsequent litter decomposability. Litter decomposability appeared proximately linked to initial litter quality, with particularly clear negative correlations with lignin-dependent indices ( litter lignin concentration, lignin : nitrogen ratio, and fiber component). Litter quality was directly related to community-weighted mean traits. Lignin-dependent indices of litter quality were positively correlated with community-weighted mean leaf dry matter content (LDMC), and negatively correlated with community-weighted mean leaf nitrogen concentration (LNC). Consequently, litter decomposability was correlated negatively with community-weighted mean LDMC, and positively with community-weighted mean LNC. Environmental factors ( disturbance and climate) influenced community-weighted mean traits. Plant communities experiencing less frequent or less intense disturbance exhibited higher community-weighted mean LDMC, and therefore higher litter lignin content and slower litter decomposability. LDMC therefore appears as a powerful marker of both changes in land use and of the pace of nutrient cycling across 10 contrasting sites.