Authors:W. Qi, X. Zhou, M. Ma, J. M. H. Knops, W. Li, and G. Du
Despite a long history of alpine meadows studies, uncertainty remains about the importance of environmental factors in structuring their assembly. We examined the functional and phylogenetic structure of 170 alpine Tibetan meadow communities in relation to elevation, soil moisture and shade. Functional community structure was estimated with both communityweighted mean (CWM) trait values for specific leaf area (SLA), plant height and seed mass and functional diversity (Rao’s quadratic index) for their traits individually and in combination (multivariate functional diversity). We found that shade induced by woody plants significantly increased the phylogenetic diversity and functional diversity of SLA of co-occurring species, suggesting that woody plants behave as “ecosystem engineers” creating a different environment that allows the existence of shade tolerant species and thereby facilitates the coexistence of plant species with different light resource acquisition strategies. We also found evidence for a clear decrease in phylogenetic diversity, CWM and functional diversity related to plant height in the two extreme, both the dry and wet, soil moisture conditions. This indicates that both drought and excess moisture may act as environmental filters selecting species with close phylogenetic relationships and similar height. Moreover, we detected significant decreases in both CWM and functional diversity for seed mass along elevational gradients, suggesting that low net primary productivity (NPP) limits seed size. Finally, because of different individual trait responses to environmental factors, the multivariate functional diversity did not change across environmental gradients. This lack of multivariate response supports the hypothesis that multiple processes, such as environmental filtering, competition and facilitation, may operate simultaneously and exert opposing effects on community assembly along different niche (e.g., water use, light acquisition) axes, resulting in no overall functional community structure change. This contrast between individual and multivariate trait patterns highlights the importance of examining individual traits linked with different ecological processes to better understand the mechanisms of community assembly.
Authors:A. Huertas Herrera, M. V. Lencinas, and G. Martínez Pastur
The comprehensive assessment of environmental gradients influencing species assemblages is important for implementing new conservation strategies under climate change. This study aims to determine the multi-scale effect of altitudinal and longitudinal gradients as drivers of richness and plant community assembly in mountain landscapes of Isla de los Estados (Argentina) to identify areas with greater conservation value in Southern Patagonia. We chose three fjords across the island that extends from West to East and we categorized landscapes into four ecosystem types according to their vegetation type (forests and open-lands) and elevation (lower lands, 0-100 m.a.s.l. and upper lands, 300-400 m.a.s.l.). Forest structure, soil cover (woody debris, rocky outcrop and bare soil) and vegetation cover (vascular and non-vascular), including richness and growthforms (trees, shrubs, prostrate and erect herbs, tussock and rhizomatous grasses, ferns and inferior plants) were measured in 60 sampling areas (3 fjords × 2 vegetation types × 2 elevations × 5 replicates). ANOVAs and multivariate methods were used to analyse heterogeneity in forest structure, plant richness, and life-form. In addition, species richness and the Simpson’s diversity index were calculated to understand plant assembly at multiple-scales (α, β and γ). Our results showed that environmental gradients (altitudinal and longitudinal) are more important drivers of change of ecosystem type than forest spatial structure. Furthermore, forest structure significantly varied with altitudinal and longitudinal gradients affecting most of the studied variables. A greater similarity (in richness and cover) between open-lands of lower and higher elevations was detected, as well as between forests. Fjords showed a West-East gradient, where the western and center fjords were more closely related to each other than to the eastern fjord. A multi-scale diversity approach may play central role in improving our understanding the main environmental drivers of richness and plant community assembly in these forests, both theoretical and empirical, and may be used to identify the spatial scale at which ecosystem types have greater conservation value. This study indicates that for southern forest conservation at regional level, efforts must cover all environmental gradients, including the different vegetation types to assure ful conservation of all the species assemblages.
Authors:S. Fanfard, F. Charles, J. Coston-Guarini, C. Nozais, and J.-M. Guarini
The ecological process of community assembly is described as the succession of three phases: colonization, regulation and segregation. Early colonization remains the least studied and quantified phase of assembly. In order to fill this gap, an approach combining in situ experiments and modelling was proposed to study colonization by a benthic macrofauna community in open microcosms containing a single, non-limiting resource. The experiment was three months long. A total of 51 taxa were observed in the microcosms, but data analyses of the species composition and abundances revealed that five species, Capitella spp., Gammaropsis maculata, Erichtionus punctatus, Nereiphylla paretti and Harmothoe mariannae, explained most of the observed variation in the assembly process. The population dynamics of these species were simulated taking into account functional traits that govern individual interactions. The dynamic model simulated a demographic stochasticity due to low population densities that result from the small size of the experimental microcosms. Using this combined approach of experiments and modelling, we showed that predation interactions alone can account for the abundances and species composition of primary consumers during the transient phase of early colonization.
Authors:V. Marcilio-Silva, V. D. Pillar, and M. C. M. Marques
Changes in species composition during the succession of ecological communities potentially reflect the differential effects of environmental filters and limiting similarity on structuring communities. As ecological succession can represent community assembly in action, understanding how successional time affects the functional and phylogenetic structure of communities can reveal the influence of different factors on the assembly process. We analysed functional patterns of multiple traits related to the succession of tropical forests to answer if there are trait convergence and/or divergence with regeneration age, and if functional and phylogenetic diversity can be predicted by forest age. We compiled checklists from studies of 23 successional forests in Brazilian Atlantic Forest, ranging from 4 to 120 years old. We also compiled functional traits for a total of 355 species. We analysed the data by a method that includes scaling-up trait-based data to the community level and matrix correlations of multiple traits. We built linear models to show the relationship between each trait and diversity (taxonomic, functional and phylogenetic) with successional time. We found no phylogenetic signal at the species pool and metacommunity levels, but significant trait divergence (tree guild, leaf slenderness, leaf area, pollination entomophilous generalist and pollination by vertebrate) and trait convergence (arboreal habitus, tree guild, leaf compoundness, pollination entomophilous generalist) patterns related to the successional gradient. Also, functional diversity increased during succession, with a significant increase in leaf slenderness and zoochoric dispersal and decrease in tree guild. Phylogenetic diversity also increased along the successional gradient. We found that the communities in the studied successional gradient are structured by both environmental (measured by trait convergence) and biotic (measured by trait divergence) filtering. The species turnover and diversification at taxonomic level are followed by well-defined patterns of trait turnover, revealing that community assembly is constrained by environmental filters at the beginning and by limiting similarity at the advanced stages of the succession.
Authors:V. J. Debastiani, S. C. Muller, J. M. Oliveira, F. S. Rocha, M. C. Sestren-Bastos, and L. D. S. Duarte
The phylogenetic relationship among species may influence the mechanisms controlling local community assembly in ecological time. We analyzed the degree of recurrence of phylogenetic structure patterns in woody plant communities distributed along grassland-forest ecotones, across different vegetation types in southern Brazil, and the effect of phylogenetic pool size used to assess such patterns. Species frequency in quadrats distributed along grassland-forest ecotones was surveyed in different phytogeographic regions, where forests tend to expand over grasslands. We used principal coordinates of phylogenetic structure (PCPS) to evaluate the structure within vegetation quadrats divided into three habitat categories: grassland, forest edge and forest interior. Furthermore, phylogenetic structure measures were computed using different phylogenetic pool sizes. Our analyses showed consistent patterns in relation to habitat categories and to different phylogenetic pool sizes. Basal clades of angiosperms were associated with forest areas, while late-divergence clades were associated with grasslands. These results suggest that grasslands act as phylogenetic habitat filters to forest woody species, independently of species composition at each site and the phylogenetic pool. Rosanae and Asteranae act as vanguards of forest expansion over grasslands, while Magnolianae species tend to be restricted to forest. Our results shed light on the organization of ecological systems, providing evidence of recurrent phylogenetic structure patterns in ecotone plant communities at regional scale.
Authors:F. Bello, J. Lepš, S. Lavorel, and M. Moretti
Measurements of trait community composition are known to be sensitive to the way species abundance is assessed, but not to what extent. This was investigated by considering two of the most commonly used indices of community trait composition, trait averages and functional diversity, in bee communities along a post-fire environmental gradient. The indices were computed using three different species abundance measurements (log and unlog number of individuals and species occurrence only) and 5 traits. For certain traits, the responses of the indices to fire varied according to how species abundance was measured. The measurements that took species abundance into account in the most distinct way (e.g., occurrence vs. unlog data) produced the least similar results for all traits. Species were then grouped into different classes on the basis of their relative abundance (i.e., dominants, subdominants, and rare species). As a result, the measure that attaches the highest importance to the abundance of species (unlog data) related mostly to the dominant species traits, while the measure attaching the lowest (i.e., species occurrence) related more to rare species traits. Species diversity was mostly independent of trait averages and functional diversity, regardless of the measure of species abundance used. We also quantified functional redundancy (i.e., the potential minus the observed functional diversity in each community). When more weight was attached to species abundance, redundancy decreased and tended to be less correlated with species diversity. Overall, the way species abundance is taken into consideration in indices of functional composition offers promising insights into the way community assembly mechanisms respond to environmental changes.