Global patterns of plant diversity

Summary Using 94 data sets from across the globe, we explored patterns of mean community species richness, landscape species richness, mean similarity among communities and mosaic diversity. Climate affected community species richness primarily through productivity while other climatic factors were secondary. Climatic equability affected species richness only in temperate regions where richness was greatest at high levels of temperature variability and low levels of precipitation variability. Landscape species richness correlated positively with community species richness. A global gradient in mean similarity existed but was uncorrelated with community species richness. Mean similarity was least and mosaic diversity was greatest between 25 and 30° latitude. The most diverse landscapes (low mean similarity) correlated with warm temperatures, high elevations, large areas and large seasonal temperature fluctuations. The most complex landscapes (high mosaic diversity) correlated with large areas, high productivity and warm winters. We compared diversity measures among continents and found only one significant difference: Australian landscapes have greater mosaic diversity than African landscapes. Based on our analyses we propose two hypotheses: (1) for plants, biotic interactions are more important in structuring landscapes in warmer climates and (2) longer isolated landscapes have more clearly differentiated ecological subunits.     

Global patterns of Sphagnum productivity

Abstract

Data from 55 published studies of Sphagnum productivity were compiled covering 31 peat-moss species from Sphagnum-dominated wetlands. The relationships between productivity and geographical position and climatic parameters were investigated based on data from both the northern and southern hemispheres. There were interspecific differences in productivity, which could be explained by both phylogeny and microhabitat preferences. Species of section Cuspidata had greater productivity than species of section Acutifolia. The wetter microhabitat carpets and lawns had higher productivity than the drier hummocks. Climatic conditions (mean annual temperature and precipitation), together with geographical factors, were able to explain 40 % of the variation in productivity. The most important single factor explaining productivity on a global scale in Sphagnum-dominated wetlands was the mean annual temperature. Climatic parameters, together with geographical position, are important for estimating the global patterns of Sphagnum productivity, and can be used to estimate productivity changes in Sphagnum-dominated wetlands under climatic warming scenarios.     

Global patterns in peatmoss biodiversity

DNA sequence data from the nuclear ribosomal internal transcribed spacers (ITS) and the trnL-trnF chloroplast DNA regions were used to quantify geographical partitioning of global biodiversity in peatmosses (Sphagnum), and to compare patterns of molecular diversity with patterns of species richness. Molecular diversity was estimated for boreal, tropical, Neotropical, nonboreal (tropical plus Southern Hemisphere), Old World and New World partitions, based on a total of 436 accessions. Diversity was partitioned among geographical regions in terms of combined nuclear and chloroplast sequence data and separately for the ITS and trnL-trnF data sets. Levels of variation were estimated using phylogenetic diversity (PD), which incorporates branch lengths from a phylogenetic tree, and the number of polymorphic nucleotide sites. Estimates of species richness suggest that peatmoss diversity is higher in New World than Old World regions, and that the Neotropics constitute a "hotspot" of diversity. Molecular estimates, in contrast, indicate that peatmoss biodiversity is almost evenly divided between New and Old World regions, and that the Neotropics account for only 20-35% of global peatmoss diversity. In general, levels of tropical and boreal peatmoss molecular diversity were comparable. Two species, S. sericeum from the Old World tropics and S. lapazense from Bolivia, are remarkably divergent in nucleotide sequences from all other Sphagna and together account for almost 20% of all peatmoss diversity, although they are represented by only three of the 436 accessions (0.7%). These species clearly demonstrate the nonequivalence of species biodiversity value.     

Global patterns in seed size

Aim  To provide the first global quantification of the slope and shape of the latitudinal gradient in seed mass, and to determine whether global patterns in seed mass are best explained by growth form, vegetation type, seed dispersal syndrome, or net primary productivity (NPP).
Location  Global.
Methods  We collected seed mass data for 11,481 species × site combinations from around the world. We used regression to describe the latitudinal gradient in seed mass, then applied general linear models to quantify the relative explanatory power of each of the variables hypothesized to underlie the latitudinal gradient in seed size.
Results  There is a 320-fold decline in geometric mean seed mass between the equator and 60°. This decline is not linear. At the edge of the tropics, there is a sudden 7-fold drop in mean seed mass. The strongest correlates of the latitudinal gradient in seed mass are plant growth form, and vegetation type, followed by dispersal syndrome and NPP. A model including growth form, vegetation type, dispersal syndrome and NPP explains 51% of the variation in seed mass. Latitude explains just 0.2% of the residual variation from this model.
Main conclusions  This is the first demonstration of a major decrease in seed size at the edge of the tropics. This drop in seed mass is most closely correlated with changes in plant growth form and vegetation type. This suggests that the drop in seed mass might be part of a sudden change in plant strategy at the edge of the tropics.     

Global patterns in belowground communities

Although belowground ecosystems have been studied extensively and soil biota play integral roles in biogeochemical processes, surprisingly we have a limited understanding of global patterns in belowground biomass and community structure. To address this critical gap, we conducted a meta-analysis of published data (> 1300 datapoints) to compare belowground plant, microbial and faunal biomass across seven of the major biomes on Earth. We also assembled data to assess biome-level patterns in belowground microbial community composition. Our analysis suggests that variation in microbial biomass is predictable across biomes, with microbial biomass carbon representing 0.6–1.1% of soil organic carbon ( r ² = 0.91) and 1–20% of total plant biomass carbon ( r ² = 0.42). Approximately 50% of total animal biomass can be found belowground and soil faunal biomass represents < 4% of microbial biomass across all biomes. The structure of belowground microbial communities is also predictable: bacterial community composition and fungal : bacterial gene ratios can be predicted reasonably well from soil pH and soil C : N ratios respectively. Together these results identify robust patterns in the structure of belowground microbial and faunal communities at broad scales which may be explained by universal mechanisms that regulate belowground biota across biomes.     

Global patterns in fruiting seasons

Aim   To identify geographical and climatic correlates of the timing of fruit production in fleshy fruited plant communities.
Location   Global.
Methods   We searched the literature for studies documenting monthly variation in the number of fleshy fruited species bearing ripe fruits in plant communities (i.e. fruit phenologies). From these data, we used circular vector algebra to characterize seasonal peaks in fruit production (mean date, as an angle) and the length of fruiting seasons (as a circular standard deviation). Generalized linear models and circular correlations were used to assess whether latitudinal patterns in fruit phenologies could be explained by variation in temperature, precipitation and actual evapotranspiration (AET).
Results   Dates of peak fruit production and the length of fruiting seasons showed consistent differences with latitude. Annual peaks in fruit production occurred 1 to 3 months after the summer solstice at high-latitude sites in both hemispheres. Fruiting seasonality increased with latitude, indicating that fruiting seasons were longer in the tropics and shorter toward the poles. AET was the best climatic predictor of fruit phenologies. Annual peaks in fruit production were positively associated with annual peaks in AET and temperature, while fruiting seasons were shorter in areas with pronounced annual variation in AET.
Main conclusions   Global patterns in fruiting seasons are associated with global variation in climate. Across the globe, fleshy fruits are produced after annual periods of elevated water–energy availability. Fruiting seasonality is also more pronounced in areas with strongly seasonal water–energy inputs. Therefore, the timing of reproduction in fleshy fruited plant communities appears to be determined, at least in part, by spatial and temporal variation in energy supplies needed to subsidise plant reproduction.     

Global patterns of amphibian phylogenetic diversity

Aim Phylogenetic diversity can provide insight into how evolutionary processes may have shaped contemporary patterns of species richness. Here, we aim to test for the influence of phylogenetic history on global patterns of amphibian species richness, and to identify areas where macroevolutionary processes such as diversification and dispersal have left strong signatures on contemporary species richness. Location Global; equal‐area grid cells of approximately 10,000 km². Methods We generated an amphibian global supertree (6111 species) and repeated analyses with the largest available molecular phylogeny (2792 species). We combined each tree with global species distributions to map four indices of phylogenetic diversity. To investigate congruence between global spatial patterns of amphibian species richness and phylogenetic diversity, we selected Faith’s phylogenetic diversity (PD) index and the total taxonomic distinctness (TTD) index, because we found that the variance of the other two indices we examined (average taxonomic distinctness and mean root distance) strongly depended on species richness. We then identified regions with unusually high or low phylogenetic diversity given the underlying level of species richness by using the residuals from the global relationship of species richness and phylogenetic diversity. Results Phylogenetic diversity as measured by either Faith’s PD or TTD was strongly correlated with species richness globally, while the other two indices showed very different patterns. When either Faith’s PD or TTD was tested against species richness, residuals were strongly spatially structured. Areas with unusually low phylogenetic diversity for their associated species richness were mostly on islands, indicating large radiations of few lineages that have successfully colonized these archipelagos. Areas with unusually high phylogenetic diversity were located around biogeographic contact zones in Central America and southern China, and seem to have experienced high immigration or in situ diversification rates, combined with local persistence of old lineages. Main conclusions We show spatial structure in the residuals of the relationship between species richness and phylogenetic diversity, which together with the positive relationship itself indicates strong signatures of evolutionary history on contemporary global patterns of amphibian species richness. Areas with unusually low and high phylogenetic diversity for their associated richness demonstrate the importance of biogeographic barriers to dispersal, colonization and diversification processes.     

Global patterns of leaf mechanical properties

Leaf mechanical properties strongly influence leaf lifespan, plant-herbivore interactions, litter decomposition and nutrient cycling, but global patterns in their interspecific variation and underlying mechanisms remain poorly understood. We synthesize data across the three major measurement methods, permitting the first global analyses of leaf mechanics and associated traits, for 2819 species from 90 sites worldwide. Key measures of leaf mechanical resistance varied c. 500-800-fold among species. Contrary to a long-standing hypothesis, tropical leaves were not mechanically more resistant than temperate leaves. Leaf mechanical resistance was modestly related to rainfall and local light environment. By partitioning leaf mechanical resistance into three different components we discovered that toughness per density contributed a surprisingly large fraction to variation in mechanical resistance, larger than the fractions contributed by lamina thickness and tissue density. Higher toughness per density was associated with long leaf lifespan especially in forest understory. Seldom appreciated in the past, toughness per density is a key factor in leaf mechanical resistance, which itself influences plant-animal interactions and ecosystem functions across the globe.     

Global patterns of aquatic food chain length

Food chain length is a fundamental ecosystem property, and plays a central role in determining ecosystem functioning. Recent advances in the field of stable isotope ecology allow the estimation of food chain length (FCL) from stable nitrogen isotope (δ¹⁵N) data. We conducted a global literature synthesis and estimated FCL for 219 lake, stream, and marine ecosystems. Streams had shorter food chains (∼3.5 trophic levels) than marine and lake ecosystems (∼4.0 trophic levels). In marine systems, inclusion of marine mammals increased FCL by 2/3 of a trophic level. For each ecosystem type, estimates of FCL were normally distributed and spanned two full trophic levels. Comparison with published connectance food webs revealed similar mean FCL values, though stable isotope-derived FCL estimates were less variable. At the global scale, FCL showed weak or no relationships with ecosystem size, mean annual air temperature, or latitude. Our study highlights the utility of stable isotopes for quantifying among-system food web variability, and the application of this approach for assessing global-scale patterns of food chain length.     

Global patterns of the double mutualism phenomenon

A double mutualism (DM) occurs when two interacting species benefit each other in two different functions, e.g. when an animal species acts both as pollinator and seed disperser of the same plant. Besides the double benefit, a DM also imposes a larger risk to both functions if the performance of one partner declines. We conducted the first global review of DMs involving pollinators and seed dispersers, aiming to: 1) assess their prevalence across ecosystems and biogeographical regions; 2) identify the main plant and animal taxa, and their traits, implicated in DMs; and 3) evaluate the conservation status of double mutualist species. We compiled published and unpublished DM records using specific search terms, noting the species involved, their conservation status and geographic location, as well as the type of study (species vs community‐level) in which the DM was detected. We identified 302 DM cases involving 207 plant and 92 animal species from 16 mainland and 17 island areas. Most records come from tropical regions and islands. Animals included birds (62%), mammals (22%), and reptiles (16%), mostly opportunist species; only 18% were nectarivores. Plants were mainly fleshy‐fruited shrub or tree species (59%) with actinomorphic flowers that were visited by several or many pollinator species (87%). Most (56%) DMs were detected in community‐level studies. DMs are mostly prevalent in ecosystems with limited food resources and mutualist partners, and with high generalization levels. Nearly 30% of the species involved in DMs are threatened according to IUCN criteria, 68% of which are found on islands. The high prevalence of DM on islands paired with the threat status of island species suggest that the loss of a double mutualists and its cascading consequences may have a severe impact on community composition and functioning of fragile island ecosystems.     

Global methylation patterns in idiopathic pulmonary fibrosis

Background

Idiopathic Pulmonary Fibrosis (IPF) is characterized by profound changes in the lung phenotype including excessive extracellular matrix deposition, myofibroblast foci, alveolar epithelial cell hyperplasia and extensive remodeling. The role of epigenetic changes in determining the lung phenotype in IPF is unknown. In this study we determine whether IPF lungs exhibit an altered global methylation profile.

Methodology/Principal Findings

Immunoprecipitated methylated DNA from 12 IPF lungs, 10 lung adenocarcinomas and 10 normal histology lungs was hybridized to Agilent human CpG Islands Microarrays and data analysis was performed using BRB-Array Tools and DAVID Bioinformatics Resources software packages. Array results were validated using the EpiTYPER MassARRAY platform for 3 CpG islands. 625 CpG islands were differentially methylated between IPF and control lungs with an estimated False Discovery Rate less than 5%. The genes associated with the differentially methylated CpG islands are involved in regulation of apoptosis, morphogenesis and cellular biosynthetic processes. The expression of three genes (STK17B, STK3 and HIST1H2AH) with hypomethylated promoters was increased in IPF lungs. Comparison of IPF methylation patterns to lung cancer or control samples, revealed that IPF lungs display an intermediate methylation profile, partly similar to lung cancer and partly similar to control with 402 differentially methylated CpG islands overlapping between IPF and cancer. Despite their similarity to cancer, IPF lungs did not exhibit hypomethylation of long interspersed nuclear element 1 (LINE-1) retrotransposon while lung cancer samples did, suggesting that the global hypomethylation observed in cancer was not typical of IPF.

Conclusions/Significance

Our results provide evidence that epigenetic changes in IPF are widespread and potentially important. The partial similarity to cancer may signify similar pathogenetic mechanisms while the differences constitute IPF or cancer specific changes. Elucidating the role of these specific changes will potentially allow better understanding of the pathogenesis of IPF.     

Global and regional patterns in lotic meiofauna

• 1 Parsimony analysis of endemicity (PAE) was used to assess patterns in the distribution of harpacticoid copepods (all freshwater species and stream species only) at global and regional scales. These analyses provided a focus for reviewing large scale patterns and processes in freshwater meiofauna.
• 2 On a global scale, PAE suggested that large‐scale biogeographical events have been most important in shaping present‐day distributions in the Canthocamptidae. A small proportion (4%) of canthocamptid species were widespread (i.e. occurred in more than one biogegraphical region), suggesting that dispersal may also play a role in determining distribution at the species level. Global distribution patterns for other meiofauna suggest varying roles for dispersal and vicariant events. No consistent latitudinal trends in species diversity were evident, although a lack of distributional data for many regions, and uncertainty over the status of many cosmopolitan species, precludes more robust analyses. Molecular techniques should prove useful in identifying truly cosmopolitan taxa.
• 3 On a regional scale, a PAE within Western Europe demonstrated a clear link between the distribution of canthocamptid species and the extent of the Last (Wiechselian) glaciation. Northern and southern areas of Europe contain distinctive harpacticoid faunas and the recolonisation of northern Europe appears to have been from the Balkans rather than other Mediterranean peninsulae. The high harpacticoid diversity in southern Europe, may reflect a lack of glacial disruption of groundwater habitats.
• 4 A PAE of lotic data for harpacticoid copepods within the Holarctic reflected the global PAE for freshwater harpacticoids as a whole, but not the regional PAE. A high proportion of stream‐dwelling harpacticoids are widespread species, but only one (Bryocamptus zschokkei) was found in streams across the Holarctic. Other cosmopolites were restricted to streams in Europe or North America, suggesting that species‘ niche requirements might differ among regions. There appeared to be some convergence in the composition of lotic copepod communities in terms of the number of species within genera.
• 5 We conclude that large‐scale processes inevitably have a major influence on the local composition of lotic meiofaunal communities, but that the relative importance of small scale vs. large scale processes is unclear at present, largely due to a paucity of suitable data.

     

Global patterns of resilience decline in vertebrate populations

Maintaining the resilience of natural populations, their ability to resist and recover from disturbance, is crucial to prevent biodiversity loss. However, the lack of appropriate data and quantitative tools has hampered our understanding of the factors determining resilience on a global scale. Here, we quantified the temporal trends of two key components of resilience—resistance and recovery—in >2000 population time-series of >1000 vertebrate species globally. We show that the number of threats to which a population is exposed is the main driver of resilience decline in vertebrate populations. Such declines are driven by a non-uniform loss of different components of resilience (i.e. resistance and recovery). Increased anthropogenic threats accelerating resilience loss through a decline in the recovery ability—but not resistance—of vertebrate populations. These findings suggest we may be underestimating the impacts of global change, highlighting the need to account for the multiple components of resilience in global biodiversity assessments.