Elevational Diversity Gradients Research Articles

An Elevational Phylogeographic Diversity Gradient in Neotropical Birds Is Decoupled from Speciation Rates.

AbstractA key question about macroevolutionary speciation rates is whether they are controlled by microevolutionary processes operating at the population level. For example, does spatial variation in population genetic differentiation underlie geographical gradients in speciation rates? Previous work suggests that speciation rates increase with elevation in Neotropical birds, but underlying population-level gradients remain unexplored. Here, we characterize elevational phylogeographic diversity between montane and lowland birds in the megadiverse Andes-Amazonian system and assess its relationship to speciation rates to evaluate the link between population-level differentiation and species-level diversification. We aggregated and georeferenced nearly 7,000 mitochondrial DNA sequences across 103 species or species complexes in the Andes and Amazonia and used these sequences to describe phylogeographic differentiation across both regions. Our results show increased levels of both discrete and continuous metrics of population structure in the Andean mountains compared with the Amazonian lowlands. However, higher levels of population differentiation do not predict higher rates of speciation in our dataset. Multiple potential factors may lead to our observed decoupling of initial population divergence and speciation rates, including the ephemerality of incipient species and the multifaceted nature of the speciation process, as well as methodological challenges associated with estimating rates of population differentiation and speciation.

Catch me if you can, or how paradigms of tardigrade biogeography evolved from cosmopolitism to ‘localism’

Abstract This review synthesizes recent developments in the field of tardigrade biogeography, tracing back to the origins of Baas Becking’s hypothesis that ‘everything is everywhere but the environment selects’ to the latest empirical studies that favour biogeographic structuring of these microinvertebrates. I recapitulate evidence for diverse means of meiofauna dispersal, focusing on the two principal mechanisms suggested for tardigrades: wind (aeolian dispersal/anemochory) and animals (zoochory). I argue that tardigrade species with relatively well-documented geographic distributions display climatic regionalization. The literature treating purportedly cosmopolitan tardigrades is critically scrutinized and evidence for strict cosmopolitanism is deemed insufficient. Due to the presence of numerous endemics restricted to mountains, elevational diversity gradients can be recognized at a local scale (for example, within a single biogeographic region). Finally, the tardigrade faunas of a given region should be likely regarded as part of a regionalized macrometazoan fauna containing a small fraction of widespread, ubiquitous species (called ‘biogeographic noise’ herein).

Environmental drivers of earthworm communities along an elevational gradient in the French Alps

Elevational diversity gradients describe how species diversity and richness change with elevation. In this study, we tested for the effect of climate, resource quality and habitat heterogeneity on earthworm communities along an elevational gradient and around the treeline in the French Alps. Earthworm communities and environmental properties (i.e. climate, soil properties, vegetation structure and composition) were sampled at six elevations ranging from 1400 to 2400 m. Results were analysed through multi-table factorial analyses and structural equation modelling. We found average density, biomass and species richness in the range of that usually reported in comparable ecosystems. We found no monotonic decrease in species richness along the elevational gradient, which we explain by the species pool being dominated by taxa with high environmental tolerance and dispersal capacities. Instead, we highlighted the ecotone associated with the treeline as the primary driving factor of earthworm communities: at 1800–2000 m elevation, communities were more abundant and diverse, and had a greater variability in body mass. This result was largely explained by the structure and composition of the vegetation, whereas soil and climate appeared to have only indirect effects. Therefore, the treeline effect on earthworm communities can be explained both by the effect of environmental heterogeneity and of trophic resource quality that increases at the ecotone level.

Humboldt's legacy: explaining the influence of environmental factors on the taxonomic and phylogenetic diversity of angiosperms along a Neotropical elevational gradient.

The scientific work of Alexander von Humboldt was influenced by his interaction with the diversity and natural wealth of the Neotropics. He proposed that climate determines plant diversity along elevational gradients based on his observations. Here, we evaluated the most prominent climate-based hypotheses in explaining plant diversity along an elevational gradient that Humboldt himself visited during his journey across Mexico. Specifically, we examined how climatic variables and forest-use intensity affected species richness and phylogenetic structure of major angiosperm life forms (trees, shrubs, epiphytes, herbs and lianas) along the Cofre de Perote mountain, Veracruz, Mexico. We analysed species richness and phylogenetic structure of angiosperms at eight sites between 30 to 3500 m a.s.l. We estimated the phylogenetic structure using a mega-phylogeny of angiosperms and the abundance-weighted net relatedness index. We considered multiple environmental factors' direct and indirect effects by applying a piecewise structural equation modelling approach. Each life form responds differently to the environmental variables included in our model; however, it is observed that temperature is the main predictor of the taxonomic and phylogenetic diversity of the angiosperms studied, both when the different life forms are grouped and separated. Potential evapotranspiration and precipitation are variables that also influence some life forms' diversity, especially taxonomic diversity. The forest-use intensity negatively affected only the taxonomic diversity of trees. These results highlight the influence of studying the different life forms of angiosperms in diversity gradient models and show the great influence that temperature has in conjunction with other environmental variables to promote the taxonomic and phylogenetic diversity of plant communities. Given the current global environmental crisis, an integrative biogeographically oriented vision based on Humboldt's method is necessary. Honouring the work of Humboldt and continuing his legacy demands more research to understand the causes behind elevational diversity gradients.

Morpho-anatomical trait variability of the Norway spruce (Picea abies (L.) Karst.) needles in natural populations along elevational diversity gradient

Morpho-anatomical trait variability of the Norway spruce (Picea abies (L.) Karst.) needles in natural populations along elevational diversity gradient

A global analysis of urbanization effects on amphibian richness: Patterns and drivers

Urbanization presents an unplanned and highly replicated global experiment to understand biotic responses to global changes. Here we conducted a global analysis on patterns and drivers of urbanization effects on biodiversity using the global amphibian richness dataset along with background climate and the continuous rural-urban gradients. We, for the first time, empirically generalized the urbanizational gradients of amphibian richness at the global scale and in different climate zones despite the substantial differences in history, ecological context, and socioeconomic conditions across large geospatial extents. We found a positive imprint of urbanization on amphibian richness in cool and climate zones whereas the presence of urban thermal stress in high temperature climate zones. Anthropogenic forces behind the urbanization gradients entangled with environmental variables directly and indirectly drove the patterns as revealed by the structural equation modeling (SEM). The urbanizational diversity gradient (UDG) found in this study might signify the existence of another general principle in ecology analogous to well-known latitudinal and elevational diversity gradients. We proposed the heat-and-threat balance (HATB) hypothesis to explain UDG: urbanization-induced heat would promote biodiversity if the ambient temperatures are cooler than their optima. Alternatively, it may put threats on biodiversity when the ambient temperatures are close to their optima. There is an urgent need to advance the knowledge on UDG in an urbanizing planet by additional studies from diverse taxa, various geographical locations, and at different scales.

Evolutionary dynamics of the elevational diversity gradient in passerine birds.

Low-elevation regions harbour the majority of the world's species diversity compared to high-elevation areas. This global gradient suggests that lowland species have had more time to diversify, or that net diversification rates have been higher in the lowlands. However, highlands seem to be cradles of diversity as they contain many young endemics, suggesting that their rates of speciation are exceptionally fast. Here we use a phylogenetic diversification model that accounts for the dispersal of species between different elevations to examine the evolutionary dynamics of the elevational diversity gradient in passerine birds, a group that has radiated globally to occupy almost all elevations and latitudes. We find strong support for a model in which passerines diversify at the same rate in the highlands and the lowlands but in which the per-capita rate of dispersal from high to low elevations is more than twice as fast as that in the reverse direction. This suggests that while there is no consistent trend in diversification across elevations, part of the diversity generated by highland regions migrates into the lowlands, thus setting up the observed gradient in passerine diversity. We find that this process drives tropical regions but for temperate areas, the analysis could be hampered by their lower richness. Despite their lower diversity, highland regions are disproportionally important for maintaining diversity in the adjacent lowlands.

Contrasting Gymnosperm Diversity Across an Elevation Gradient in the Ecoregion of China: The Role of Temperature and Productivity

The species richness–climate relationship is a significant concept in determining the richness patterns and predicting the cause of its distribution. The distribution range of species and climatic variables along elevation have been used in evaluating the elevational diversity gradients (EDG). However, the species richness of gymnosperms along elevation and its driving factors in large geographic areas are still unknown. Here, we aimed at evaluating the EDG of gymnosperms in the ecoregions of China. We divided the geographical region of China into 34 ecoregions and determine the richness pattern of gymnosperm taxa along elevation gradients. We demonstrated the richness patterns of the 237-gymnosperm (219 threatened, 112 endemic, 189 trees, and 48 shrubs) taxa, roughly distributed between 0 and 5,300 m (above sea level) in China. As possible determinants of richness patterns, annual mean temperature (TEMP), annual precipitation (PPT), potential evapotranspiration (PET), net primary productivity (SNPP), aridity index (AI), temperature seasonality (TS), and precipitation seasonality (PS) are the major predictor variables driving the EDG in plants. We used the species interpolation method to determine the species richness at each elevation band. To evaluate the richness pattern of gymnosperms in an ecoregion, generalized additive modeling and structural equation modeling were performed. The ecoregions in the southern part of China are rich in gymnosperm species, where three distinct richness patterns—(i) hump-shaped, (ii) monotonic increase, and (iii) monotonic decline—were noticed in China. All climatic variables have a significant effect on the richness pattern of gymnosperms; however, TEMP, SNPP, TS, and PS explained the highest deviance in diversity-rich ecoregions of China. Our results suggests that the highest number of gymnosperms species was found in the southwestern and Taiwan regions of China distributed at the 1,600- and 2,800-m elevation bands. These regions could be under severe stress in the near future due to expected changes in precipitation pattern and increase of temperature due to climate change. Thus, our study provided evidence of the species–climate relationship that can support the understanding of future conservation planning of gymnosperms.

Niche Conservatism Drives the Elevational Diversity Gradient in Major Groups of Free-Living Soil Unicellular Eukaryotes.

Ancestral adaptations to tropical-like climates drive most multicellular biogeography and macroecology. Observational studies suggest that this niche conservatism could also be shaping unicellular biogeography and macroecology, although evidence is limited to Acidobacteria and testate amoebae. We tracked the phylogenetic signal of this niche conservatism in far related and functionally contrasted groups of common soil protists (Bacillariophyta, Cercomonadida, Ciliophora, Euglyphida and Kinetoplastida) along a humid but increasingly cold elevational gradient in Switzerland. Protist diversity decreased, and the size of the geographic ranges of taxa increased with elevation and associated decreasing temperature (climate), which is consistent with a macroecological pattern known as the Rapoport effect. Bacillariophyta exhibited phylogenetically overdispersed communities assembled by competitive exclusion of closely related taxa with shared (conserved) niches. By contrast, Cercomonadida, Ciliophora, Euglyphida and Kinetoplastida exhibited phylogenetically clustered communities assembled by habitat filtering, revealing the coexistence of closely related taxa with shared (conserved) adaptations to cope with the humid but temperate to cold climate of the study site. Phylobetadiversity revealed that soil protists exhibit a strong phylogenetic turnover among elevational sites, suggesting that most taxa have evolutionary constraints that prevent them from colonizing the colder and higher sites of the elevation gradient. Our results suggest that evolutionary constraints determine how soil protists colonize climates departing from warm and humid conditions. We posit that these evolutionary constraints are linked to an ancestral adaptation to tropical-like climates, which limits their survival in exceedingly cold sites. This niche conservatism possibly drives their biogeography and macroecology along latitudinal and altitudinal climatic gradients.

Mammals on mountainsides revisited: Trait‐based tests of assembly reveal the importance of abiotic filters

AbstractAimMountains provide uniquely informative systems for examining how biodiversity is distributed and identifying the causes of those patterns. Elevational patterns of species richness are well‐documented for many taxa but comparatively few studies have investigated patterns in multiple dimensions of biodiversity along mountainsides, which can reveal the underlying processes at play. Here, we use trait‐based diversity patterns to determine the role of abiotic filters and competition in the assembly of communities of small mammals across elevation and evaluate the surrogacy of taxonomic, functional, and phylogenetic dimensions of diversity.LocationGreat Basin ecoregion, western North America.TaxonRodents and shrews.MethodsThe elevational distributions of 34 species were determined from comprehensive field surveys conducted in three arid, temperate mountain ranges. Elevation–diversity relationships and community assembly processes were inferred from phylogenetic (PD) and functional diversity (FD) patterns of mean pairwise and mean nearest‐neighbor distances while accounting for differences in species richness. FD indices were calculated separately for traits related to either abiotic filtering (β‐niche traits) or biotic interactions (α‐niche traits) to test explicit predictions of the role of each across elevation.ResultsTrait‐based tests of processes indicated that abiotic filtering tied to a strong aridity gradient drives the assembly of both low‐ and high‐elevation communities. Support for competition was not consistent with theoretical expectations under the stress‐dominance hypothesis, species interactions‐abiotic stress hypothesis, or guild assembly rule. Mid‐elevation peaks in species richness contrasted with overall FD and PD, which generally increased with elevation. PD and total FD were correlated on two of three mountains.Main conclusionsThe functional diversity of small mammal communities in these arid, temperate mountains is most consistent with abiotic filters, whereas support for competition is weak. Decomposing FD into traits related to separate assembly processes and examining ecoregional variation in diversity were critical for uncovering the generality of mechanisms. Divergent patterns among dimensions revealed species richness to be a poor surrogate for PD and FD across elevation and reflect the effect of biogeographic and evolutionary history. This first analysis of elevational multidimensional diversity gradients for temperate mammals provides a versatile framework for future comparative studies.

Factors that shape the elevational patterns of plant diversity in the Yatsugatake Mountains, Japan.

Elevation is involved in determining plant diversity in montane ecosystems. This study examined whether the distribution of plants in the Yatsugatake Mountains, central Japan, substantiated hypotheses associated with an elevational diversity gradient. Species richness of trees, shrubs, herbs, ferns, and bryophytes was investigated in study plots established at 200‐m elevational intervals from 1,800 to 2,800 m. The changes in plant diversity (alpha and beta diversities, plant functional types, and elevational ranges) with elevation were analyzed in relation to climatic factors and elevational diversity gradient hypotheses, that is, mass effect, mid‐domain effect, and Rapoport's elevational rule. In addition, the elevational patterns of dominance of plant functional types were also analyzed. A comparison of alpha and beta diversities revealed that different plant groups responded variably to elevation; the alpha diversity of trees and ferns decreased, that of herbs increased, whereas the alpha diversity of shrubs and bryophytes showed a U‐shaped relationship and a hump‐shaped pattern. The beta diversity of shrubs, herbs, and bryophytes increased above the subalpine–alpine ecotone. In accordance with these changes, the dominance of evergreen shrubs and graminoids increased above this ecotone, whereas that of evergreen trees and liverworts decreased. None of the plant groups showed a wide elevational range at higher elevations. These elevational patterns of plant groups were explained by climatic factors, and not by elevational diversity gradient hypotheses. Of note, the changes in the dominance of plant groups with elevation can be attributed to plant–plant interactions via competition for light and the changes in physical habitat. These interactions could alter the elevational diversity gradient shaped by climatic factors.

Distributional Patterns of Aquatic Empididae (Diptera) along an Elevational Diversity Gradient in a Low Mountain Range: An Example from Central Europe.

Simple SummaryThe insect distribution and diversity depend on many different abiotic and biotic factors, which is especially well documented in the high mountains but has not been studied in detail in the low mountain massifs. We studied 17 different macro and microhabitat factors that influence the altitudinal distribution of 40 Hemerodromiinae and Clinocerinae species in the Pieniny Mts., Poland. This is the first such study in Central Europe and one of only a few in the world. The results clearly show that species richness and distribution of Hemerodromiinae and Clinocerinae species are changing with the elevational gradient, with a monotonic decline in species richness with increasing elevation observed for the first subfamily and the hump-shaped distribution pattern noted for the second subfamily, as well as the size of the stream/river and the surrounding area in species distribution in the Pieniny Mts.The two subfamilies Hemerodromiinae and Clinocerinae, also known as aquatic dance flies, are a group of small predatory insects occurring mainly in mountainous areas and the northern temperate. However, very little is known about distribution patterns for most of the species. Habitat preferences for 40 aquatic empidid species were analysed in the Pieniny Mts., Poland. Forty-six sampling sites from a major part of this relatively low mountain massif (400–770 m) were chosen, for which 17 micro and macrohabitat environmental variables were measured including both abiotic (altitude, stream mean width and depth, and shading) and biotic factors (13 dominant plant communities). Here we show that numerous studied aquatic Empididae were characterized by unique habitat preferences and were restricted to the foothills or the lower montane zone with only a few species characterized by wider elevational distribution. Chelifera pectinicauda, C. flavella, C. subangusta and Phyllodromia melanocephala (Hemerodromiinae), and Clinocera appendiculata, C. fontinalis, C. wesmaeli, Dolichocephala guttata, D. oblongoguttata, Kowarzia plectrum, Wiedemannia jazdzewskii, and W. thienemanni (Clinocerinae) were clearly associated with the highest altitudes and shaded areas while W. bistigma, W. lamellata, W. phantasma, and W. tricuspidata (Clinocerinae) were clearly associated with the lower elevated, wider stream valleys overgrown by willow brakes. Species richness and diversity decreased along elevational gradient with the hump-shaped diversity pattern noted for the subfamily Clinocerinae. The altitude, size of river/stream as well as the type of plant community were found as the most important factors in the distribution of the studied aquatic empidid species. The present study is the first one focused on elevational diversity gradient and habitat preferences of Hemerodromiinae and Clinocerinae of central Europe, and one of only a few in the world.

Diversity, distribution and changes in communities of fleas on small mammals along the elevational gradient from the Pannonian Plain to the Carpathian Mountains - CORRIGENDUM.

The causal chain of parasite–host–environment interactions, the so-called ‘dual parasite environment’, makes studying parasites more complicated than other wild organisms. A sample of 65 282 fleas taken from 336 different locations were analysed for changes in the distribution, diversity and compensation of flea communities found on small mammals along an elevational diversity gradient ranging from the Pannonian Plain to the base of the Carpathian summits. The fleas were divided into four groups, which were derived from changes in abundance and occurrence determined from cluster analysis. They are (1) flea species whose range seems unrelated to any change in elevation; (2) species that avoid high altitudes; (3) a group that can be subdivided into two types: (i) host-specific fleas and (ii) mountains species and (4) species opting for high altitudes on the gradient or preferring lower to middle elevations below 1000 m. Our study showed a unimodal pattern of flea diversity along the elevational gradient. It indicated that seasonality significantly conditions changes in biodiversity and patterns of spatial change along the elevational gradient, with specific flea species influenced by their host, while the impact of environmental conditions is more pronounced in opportunistic flea species.

Relationships between resource availability and elevation vary between metrics creating gradients of nutritional complexity

Plant and animal community composition changes at higher elevations on mountains. Plant and animal species richness generally declines with elevation, but the shape of the relationship differs between taxa. There are several proposed mechanisms, including the productivity hypotheses; that declines in available plant biomass confers fewer resources to consumers, thus supporting fewer species. We investigated resource availability as we ascended three aspects of Helvellyn mountain, UK, measuring several plant nutritive metrics, plant species richness and biomass. We observed a linear decline in plant species richness as we ascended the mountain but there was a unimodal relationship between plant biomass and elevation. Generally, the highest biomass values at mid-elevations were associated with the lowest nutritive values, except mineral contents which declined with elevation. Intra-specific and inter-specific increases in nutritive values nearer the top and bottom of the mountain indicated that physiological, phenological and compositional mechanisms may have played a role. The shape of the relationship between resource availability and elevation was different depending on the metric. Many consumers actively select or avoid plants based on their nutritive values and the abundances of consumer taxa vary in their relationships with elevation. Consideration of multiple nutritive metrics and of the nutritional requirements of the consumer may provide a greater understanding of changes to plant and animal communities at higher elevations. We propose a novel hypothesis for explaining elevational diversity gradients, which warrants further study; the ‘nutritional complexity hypothesis’, where consumer species coexist due to greater variation in the nutritional chemistry of plants.

Diversity, distribution and changes in communities of fleas on small mammals along the elevational gradient from the Pannonian Plain to the Carpathian Mountains.

The causal chain of parasite-host-environment interactions, the so-called 'dual parasite environment', makes studying parasites more complicated than other wild organisms. A sample of 65 282 fleas taken from 336 different locations were analysed for changes in the distribution, diversity and compensation of flea communities found on small mammals along an elevational diversity gradient ranging from the Pannonian Plain to the base of the Carpathian summits. The fleas were divided into four groups, which were derived from changes in abundance and occurrence determined from cluster analysis. They are (1) flea species whose range seems unrelated to any change in elevation; (2) species that avoid high altitudes; (3) a group that can be subdivided into two types: (i) host-specific fleas and (ii) mountains species and (4) species opting for high altitudes on the gradient or preferring lower to middle elevations below 1000 m. Our study showed a unimodal pattern of flea diversity along the elevational gradient. It indicated that seasonality significantly conditions changes in biodiversity and patterns of spatial change along the elevational gradient, with specific flea species influenced by their host, while the impact of environmental conditions is more pronounced in opportunistic flea species.

Fifteen important questions in the spatial ecology of diatoms

Abstract Recently, studies about the spatial distribution of microbial species and communities have increased substantially. Freshwater diatoms are used as one of the most popular model taxa in such macroecological studies, but the most exciting patterns in the spatial ecology of diatoms have not been reviewed. Here, we identify 15 important questions about freshwater diatom ecology, review the major findings, and suggest novel research avenues. We found that diatoms do not support classical latitudinal diversity gradient, species–area relationship or Rapoport's rule. We found some, albeit inconsistent support for an elevational diversity gradient, Bergmann's rule and niche conservation. Diatoms do support a positive interspecific abundance–occupancy relationship like nearly all other taxa. With regards to metacommunity dynamics, diatom communities are typically structured by species sorting, but neutral dynamics or mass effects are also evident at large or small spatial scale, respectively. Taken together, this review suggests that diatoms follow some classical biogeographical patterns similarly to larger taxa, but patterns are typically weaker than for macro‐organisms. This may result because diatoms are typically relatively strongly controlled by local factors and often exhibit efficient stochastic dispersal processes both at small and large scales. More research is needed to build a more comprehensive view of diatom species–area relationships and latitudinal gradients in diversity, for example. In the future, well‐replicated macroecological field experiments, diatom studies with intercontinental or global coverage, trait‐based approaches, and DNA‐based species identification would be fruitful avenues to shed more light into the spatial ecology of diatoms.

Effects of boundary constraints and climatic factors on plant diversity along an altitudinal gradient

Despite the long-standing ecological interest in elevational-diversity gradients, it remains unclear whether different life forms (trees, shrubs and herbs) show the same diversity patterns along the gradient. The distribution of plants observed along an altitudinal elevation in the Lancang River Nature Reserve (Yunnan, China) was used to explore this question. We also explored the effects of boundary constraints and climatic factors on the distribution of plant diversity. Our results showed that: (1) All life forms (trees, shrubs and herbs) showed significant and similar elevational trends in richness, with the trend the most significant for trees (R2 = 0.708, p < 0.001), where species richness first increases and then decreases with increasing altitude. (2) Raw tree, shrub and herb richness are significantly correlated with each other, and shrub layer richness and herb layer richness have the greatest correlation (R2 = 0.715). (3) MAT (mean annual temperature), WMT (maximum temperature of the hottest month) and CMT (minimum temperature of the coldest month) better explained the richness patterns (raw and estimated) of different plant life forms along the elevational gradient than other climatic factors. (4) Estimated species (boundary constraint reduced) richness patterns along an elevational gradient can be better explained by climatic variables than by raw species richness for all life forms. Our findings reveal that the richness patterns of different life-forms were similar along the altitudinal gradient.

Different responses of avian feeding guilds to spatial and environmental factors across an elevation gradient in the central Himalaya.

Although elevational patterns of species richness have been well documented, how the drivers of richness gradients vary across ecological guilds has rarely been reported. Here, we examined the effects of spatial factors (area and mid‐domain effect; MDE) and environmental factors, including metrics of climate, productivity, and plant species richness on the richness of breeding birds across different ecological guilds defined by diet and foraging strategy. We surveyed 12 elevation bands at intervals of 300 m between 1,800 and 5,400 m a.s.l using line‐transect methods throughout the wet season in the central Himalaya, China. Multiple regression models and hierarchical partitioning were used to assess the relative importance of spatial and environmental factors on overall bird richness and guild richness (i.e., the richness of species within each guild). Our results showed that richness for all birds and most guilds displayed hump‐shaped elevational trends, which peaked at an elevation of 3,300–3,600 m, although richness of ground‐feeding birds peaked at a higher elevation band (4,200–4,500 m). The Normalized Difference Vegetation Index (NDVI)—an index of primary productivity—and habitat heterogeneity were important factors in explaining overall bird richness as well as that of insectivores and omnivores, with geometric constraints (i.e., the MDE) of secondary importance. Granivore richness was not related to primary production but rather to open habitats (granivores were negatively influenced by habitat heterogeneity), where seeds might be abundant. Our findings provide direct evidence that the richness–environment relationship is often guild‐specific. Taken together, our study highlights the importance of considering how the effects of environmental and spatial factors on patterns of species richness may differ across ecological guilds, potentially leading to a deeper understanding of elevational diversity gradients and their implications for biodiversity conservation.

Plant functional diversity and soil properties control elevational diversity gradients of soil bacteria.

Elevational gradients represent model systems for understanding the relationships between soil microbial communities and environmental factors, but the multiple influences of plant-soil linkages and climate conditions on elevational diversity gradients (EDGs) of soil microbes have never been explored. Here, we examined how climate conditions, plant diversity and soil properties affect EDGs of soil bacteria at different soil depths. Bacterial communities were investigated at four soil depths in 60 vegetation survey plots along elevational gradients in central Japan. In this study, elevational gradients reflected climate conditions, including mean annual temperature and seasonality of temperature and precipitation. Bacterial diversity decreased with elevation in the surface soil, but showed no relationship with elevation in deep soils. The structural equation modeling showed that soil bacterial diversity was directly affected by plant functional diversity, where leaf C:N ratio diversity had stronger effects than soil properties. We found that EDGs of soil bacteria were determined by the degree of indirect effects of climate conditions, via plant functional diversity and soil properties, against the direct effect of climate conditions on bacterial diversity. These findings demonstrate that community assembly of soil microbes is causally linked with climate conditions, plant functional diversity and soil properties, which determine EDGs.

Soil pH dominates elevational diversity pattern for bacteria in high elevation alkaline soils on the Tibetan Plateau.

Although studies of elevational diversity gradient for microbes have attracted considerable attention, the generality of these patterns and their underlying drivers are still poorly understood. Here, we investigated bacterial distribution across a high elevational gradient (4328-5228 m a.s.l.) along the Nyainqêntanglha mountains on the Southwestern Tibetan Plateau. We found a decreasing diversity trend with increasing elevation, with pH contributing most to the diversity variation, followed by elevation and mean annual temperature (MAT). Bacterial community composition differed taxonomically and phylogenetically with elevation. Furthermore, partial Mantel analyzes showed that bacterial community composition was significantly influenced by elevation, pH and MAT. Phylogenetic structure analysis indicated that deterministic processes (related to pH) determined bacterial community assembly along this elevation gradient. Our results reinforce the observed rule that pH is of foremost importance in driving bacterial elevational diversity patterns. We also suggest that absence of tree cover and of human disturbance might be important in allowing an underlying elevational trend to reveal itself. Review of other studies suggests that the trend of decreasing diversity at higher elevations might be generally true above the tree line.