Multiple facets of biodiversity drive the diversity–stability relationship

A substantial body of evidence has demonstrated that biodiversity stabilizes ecosystem functioning over time in grassland ecosystems. However, the relative importance of different facets of biodiversity underlying the diversity–stability relationship remains unclear. Here we use data from 39 grassland biodiversity experiments and structural equation modelling to investigate the roles of species richness, phylogenetic diversity and both the diversity and community-weighted mean of functional traits representing the ‘fast–slow’ leaf economics spectrum in driving the diversity–stability relationship. We found that high species richness and phylogenetic diversity stabilize biomass production via enhanced asynchrony in the performance of co-occurring species. Contrary to expectations, low phylogenetic diversity enhances ecosystem stability directly, albeit weakly. While the diversity of fast–slow functional traits has a weak effect on ecosystem stability, communities dominated by slow species enhance ecosystem stability by increasing mean biomass production relative to the standard deviation of biomass over time. Our in-depth, integrative assessment of factors influencing the diversity–stability relationship demonstrates a more multicausal relationship than has been previously acknowledged

Contrasts among cationic phytochemical landscapes in the southern United States

Understanding the phytochemical landscapes of essential and nonessential chemical elements to plants provides an opportunity to better link biogeochemical cycles to trophic ecology. We investigated the formation and regulation of the cationic phytochemical landscapes of four key elements for biota: Ca, Mg, K, and Na. We collected aboveground tissues of plants in Atriplex, Helianthus, and Opuntia and adjacent soils from 51, 131, and 83 sites, respectively, across the southern United States. We determined the spatial variability of these cations in plants and soils. Also, we quantified the homeostasis coefficient for each cation and genus combination, by using mixed-effect models, with spatially correlated random effects. Additionally, using random forest models, we modeled the influence of bioclimatic, soil, and spatial variables on plant cationic concentrations. Sodium variability and spatial autocorrelation were considerably greater than for Ca, Mg, or K. Calcium, Mg, and K exhibited strongly homeostatic patterns, in striking contrast to non-homeostatic Na. Even so, climatic and soil variables explained a large proportion of plants\u27 cationic concentrations. Essential elements (Ca, Mg, and K) appeared to be homeostatically regulated, which contrasted sharply with Na, a nonessential element for most plants. In addition, we provide evidence for the No-Escape-from-Sodium hypothesis in real-world ecosystems, indicating that plant Na concentrations tend to increase as substrate Na levels increase

Biogeographic context mediates multifaceted diversity-productivity relationships in island and mainland forests

Biotic and abiotic conditions have been found to strongly influence how biodiversity affects ecosystem functioning in forests. This context dependency of biodiversity-productivity relationships in real-world ecosystems may be shaped by the biogeographic context via deep-time processes acting on the size and composition of the species pool such as dispersal limitation, environmental filtering, speciation and invasibility. However, the role of the biogeographic context in shaping multifaceted biodiversity and forest productivity relationships remains uncertain. Using data from the Spanish National Forest Inventory in climatically similar forests on the Canary Islands (637 plots) and mainland Spain (1434 plots), we investigate the extent to which above-ground productivity is determined by ecological and evolutionary processes associated with the biogeographic context. We used structural equation models to test the drivers of above-ground productivity in both contexts, that operate via multifaceted tree diversity (taxonomic, phylogenetic, and functional diversity) or alternative mechanisms, that is environmental conditions, non-native species, and the number of trees. Our results show that mainland and island forests exhibit similar levels of productivity, yet island forests display overall lower multifaceted diversity. We found that the number of trees increased multifaceted diversity and also increased productivity directly and via their effects on phylogenetic diversity in both mainland and island forests. Further, non-native species increased productivity in island forests. Synthesis: Our results suggest that multifaceted diversity, by capturing the diversity of evolutionary history, contributes to elucidating diversity-productivity relationships in mainland and island forests that could not be detected by taxonomic diversity alone. By filling empty niches in island forests, we find that non-native species are fundamentally altering ecosystem functioning on islands and thus, reveal how biogeographic context can shape biodiversity-productivity relationships

Mapping local and global variability in plant trait distributions

Our ability to understand and predict the response of ecosystems to a changing environment depends on quantifying vegetation functional diversity. However, representing this diversity at the global scale is challenging. Typically, in Earth system models, characterization of plant diversity has been limited to grouping related species into plant functional types (PFTs), with all trait variation in a PFT collapsed into a single mean value that is applied globally. Using the largest global plant trait database and state of the art Bayesian modeling, we created fine-grained global maps of plant trait distributions that can be applied to Earth system models. Focusing on a set of plant traits closely coupled to photosynthesis and foliar respiration - specific leaf area (SLA) and dry mass-based concentrations of leaf nitrogen (Nm) and phosphorus (Pm), we characterize how traits vary within and among over 50,000 ∼50×50-km cells across the entire vegetated land surface. We do this in several ways - without defining the PFT of each grid cell and using 4 or 14 PFTs; each model's predictions are evaluated against out-of-sample data. This endeavor advances prior trait mapping by generating global maps that preserve variability across scales by using modern Bayesian spatial statistical modeling in combination with a database over three times larger than that in previous analyses. Our maps reveal that the most diverse grid cells possess trait variability close to the range of global PFT means

Assembly of functional diversity in an oceanic island flora

Oceanic island floras are well known for their morphological peculiarities and exhibit striking examples of trait evolution1–3. These morphological shifts are commonly attributed to insularity and are thought to be shaped by the biogeographical processes and evolutionary histories of oceanic islands2,4. However, the mechanisms through which biogeography and evolution have shaped the distribution and diversity of plant functional traits remain unclear5. Here we describe the functional trait space of the native flora of an oceanic island (Tenerife, Canary Islands, Spain) using extensive field and laboratory measurements, and relate it to global trade-offs in ecological strategies. We find that the island trait space exhibits a remarkable functional richness but that most plants are concentrated around a functional hotspot dominated by shrubs with a conservative life-history strategy. By dividing the island flora into species groups associated with distinct biogeographical distributions and diversification histories, our results also suggest that colonization via long-distance dispersal and the interplay between inter-island dispersal and archipelago-level speciation processes drive functional divergence and trait space expansion. Contrary to our expectations, speciation via cladogenesis has led to functional convergence, and therefore only contributes marginally to functional diversity by densely packing trait space around shrubs. By combining biogeography, ecology and evolution, our approach opens new avenues for trait-based insights into how dispersal, speciation and persistence shape the assembly of entire native island floras.Fil: Barajas Barbosa, Martha Paola. Martin-luther-Universität Halle-Wittenberg; Alemania. German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig; Alemania. Universität Göttingen; AlemaniaFil: Craven, Dylan. Data Observatory Foundation; Chile. Universidad Mayor; ChileFil: Weigelt, Patrick. Universität Göttingen; AlemaniaFil: Denelle, Pierre. Universität Göttingen; AlemaniaFil: Otto, Rüdiger. Universidad de La Laguna; EspañaFil: Díaz, Sandra Myrna. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Price, Jonathan. University Of Hawaii At Hilo; Estados UnidosFil: Fernández Palacios, José María. Universidad de La Laguna; EspañaFil: Kreft, Holger. Universität Göttingen; Alemani

Environmental gradients and the evolution of successional habitat specialization: A test case with 14 Neotropical forest sites

https://www.scopus.com/inward/record.url?eid=2-s2.0-84939570316&partnerID=40&md5=fcadae8e6c274e8b7efca96099304a7cSuccessional gradients are ubiquitous in nature, yet few studies have systematically examined the evolutionary origins of taxa that specialize at different successional stages. Here we quantify successional habitat specialization in Neotropical forest trees and evaluate its evolutionary lability along a precipitation gradient. Theoretically, successional habitat specialization should be more evolutionarily conserved in wet forests than in dry forests due to more extreme microenvironmental differentiation between early and late-successional stages in wet forest. We applied a robust multinomial classification model to samples of primary and secondary forest trees from 14 Neotropical lowland forest sites spanning a precipitation gradient from 788 to 4000 mm annual rainfall, identifying species that are old-growth specialists and secondary forest specialists in each site. We constructed phylogenies for the classified taxa at each site and for the entire set of classified taxa and tested whether successional habitat specialization is phylogenetically conserved. We further investigated differences in the functional traits of species specializing in secondary vs. old-growth forest along the precipitation gradient, expecting different trait associations with secondary forest specialists in wet vs. dry forests since water availability is more limiting in dry forests and light availability more limiting in wet forests. Successional habitat specialization is non-randomly distributed in the angiosperm phylogeny, with a tendency towards phylogenetic conservatism overall and a trend towards stronger conservatism in wet forests than in dry forests. However, the specialists come from all the major branches of the angiosperm phylogeny, and very few functional traits showed any consistent relationships with successional habitat specialization in either wet or dry forests. Synthesis. The niche conservatism evident in the habitat specialization of Neotropical trees suggests a role for radiation into different successional habitats in the evolution of species-rich genera, though the diversity of functional traits that lead to success in different successional habitats complicates analyses at the community scale. Examining the distribution of particular lineages with respect to successional gradients may provide more insight into the role of successional habitat specialization in the evolution of species-rich taxa

Current climate, isolation and history drive global patterns of tree phylogenetic endemism

AimWe mapped global patterns of tree phylogenetic endemism (PE) to identify hotspots and test hypotheses about possible drivers. Specifically, we tested hypotheses related to current climate, geographical characteristics and historical conditions and assessed their relative importance in shaping PE patterns.LocationGlobal.Time periodWe used the present distribution of trees, and predictors covering conditions from the mid‐Miocene to present.Major taxa studiedAll seed‐bearing trees.MethodsWe compiled distributions for 58,542 tree species across 463 regions worldwide, matched these to a recent phylogeny of seed plants and calculated PE for each region. We used a suite of predictor variables describing current climate (e.g., mean annual temperature), geographical characteristics (e.g., isolation) and historical conditions (e.g., tree cover at the Last Glacial Maximum) in a spatial regression model to explain variation in PE.ResultsTree PE was highest on islands, and was higher closer to the equator. All three groups of predictor variables contributed substantially to the PE pattern. Isolation and topographic heterogeneity promoted high PE, as did high current tree cover. Among mainland regions, temperature seasonality was strongly negatively related to PE, while mean annual temperature was positively related to PE on islands. Some relationships differed among the major floristic regions. For example, tree cover at the Last Glacial Maximum was a positive predictor of PE in the Palaeotropics, while tree cover at the Miocene was a negative predictor of PE in the Neotropics.Main conclusionsGlobally, PE can be explained by a combination of geographical, historical and current factors. Some geographical variables appear to be key predictors of PE. However, the impact of historic and current climate variables differs considerably among the major floristic regions, reflecting their unique histories. Hence, the current distribution of trees is the result of globally relevant geographical drivers and regional climatic histories.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153237/1/geb13001.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153237/2/geb13001_am.pd

Effects of plant diversity on productivity strengthen over time due to trait-dependent shifts in species overyielding

Plant diversity effects on community productivity often increase over time. Whether the strengthening of diversity effects is caused by temporal shifts in species-level overyielding (i.e., higher species-level productivity in diverse communities compared with monocultures) remains unclear. Here, using data from 65 grassland and forest biodiversity experiments, we show that the temporal strength of diversity effects at the community scale is underpinned by temporal changes in the species that yield. These temporal trends of species-level overyielding are shaped by plant ecological strategies, which can be quantitatively delimited by functional traits. In grasslands, the temporal strengthening of biodiversity effects on community productivity was associated with increasing biomass overyielding of resource-conservative species increasing over time, and with overyielding of species characterized by fast resource acquisition either decreasing or increasing. In forests, temporal trends in species overyielding differ when considering above- versus belowground resource acquisition strategies. Overyielding in stem growth decreased for species with high light capture capacity but increased for those with high soil resource acquisition capacity. Our results imply that a diversity of species with different, and potentially complementary, ecological strategies is beneficial for maintaining community productivity over time in both grassland and forest ecosystems

Phylogenetic composition of native island floras influences naturalized alien species richness

Islands are hotspots of plant endemism and are particularly vulnerable to the establishment (naturalization) of alien plant species. Naturalized species richness on islands depends on several biogeographical and socioeconomic factors, but especially on remoteness. One potential explanation for this is that the phylogenetically imbalanced composition of native floras on remote islands leaves unoccupied niche space for alien species to colonize. Here, we tested whether the species richness of naturalized seed plants on 249 islands worldwide is related to the phylogenetic composition of their native floras. To this end, we calculated standardized effect size (ses) accounting for species richness for three phylogenetic assemblage metrics (Faith's phylogenetic diversity (PD), PDses; mean pairwise distance (MPD), MPDses; and mean nearest taxon distance (MNTD), MNTDses) based on a phylogeny of 42 135 native island plant species and related them to naturalized species richness. As covariates in generalized linear mixed models, we included native species richness and biogeographical, climatic and socioeconomic island characteristics known to affect naturalized species richness. Our analysis showed an increase in naturalized species richness with increasing phylogenetic clustering of the native assemblages (i.e. native species more closely related than expected by chance), most prominently with MPDses. This effect, however, was smaller than the influence of native species richness and biogeographical factors, e.g. remoteness. Further, the effect of native phylogenetic structure (MPDses) on naturalized species richness was stronger for smaller islands, but this pattern was not consistent across all phylogenetic assemblage metrics. This finding suggests that the phylogenetic composition of native island floras may affect naturalized species richness, particularly on small islands where species are more likely to co-occur locally. Overall, we conclude that the composition of native island assemblages affects their susceptibility to plant naturalizations in addition to other socioeconomic and biogeographical factors, and should be considered when assessing invasion risks on islands

Phylogenetic composition of native island floras influences naturalized alien species richness

Islands are hotspots of plant endemism and are particularly vulnerable to the establishment (naturalization) of alien plant species. Naturalized species richness on islands depends on several biogeographical and socioeconomic factors, but especially on remoteness. One potential explanation for this is that the phylogenetically imbalanced composition of native floras on remote islands leaves unoccupied niche space for alien species to colonize. Here, we tested whether the species richness of naturalized seed plants on 249 islands worldwide is related to the phylogenetic composition of their native floras. To this end, we calculated standardized effect size (ses) accounting for species richness for three phylogenetic assemblage metrics (Faith’s phylogenetic diversity (PD), PDses; mean pairwise distance (MPD), MPDses; and mean nearest taxon distance (MNTD), MNTDses) based on a phylogeny of 42 135 native island plant species and related them to naturalized species richness. As covariates in generalized linear mixed models, we included native species richness and biogeographical, climatic and socioeconomic island characteristics known to affect naturalized species richness. Our analysis showed an increase in naturalized species richness with increasing phylogenetic clustering of the native assemblages (i.e. native species more closely related than expected by chance), most prominently with MPDses. This effect, however, was smaller than the influence of native species richness and biogeographical factors, e.g. remoteness. Further, the effect of native phylogenetic structure (MPDses) on naturalized species richness was stronger for smaller islands, but this pattern was not consistent across all phylogenetic assemblage metrics. This finding suggests that the phylogenetic composition of native island floras may affect naturalized species richness, particularly on small islands where species are more likely to co-occur locally. Overall, we conclude that the composition of native island assemblages affects their susceptibility to plant naturalizations in addition to other socioeconomic and biogeographical factors, and should be considered when assessing invasion risks on islands