Elevational Species Richness Patterns Research Articles

Elevational patterns of species richness and community structure of understorey birds in an East African montane forest

AbstractMt. Kasigau is the northeastern most of the Eastern Arc Mountains global hotspot and harbours some endemic and threatened species, but little is known about bird community changes along its elevational gradient. We assessed the relationship between bird biodiversity metrics, season, human disturbance, elevation and temperature using mist‐netting data collected bi‐annually over a 10‐year period. Birds were sampled along the mountain's elevational gradient at four elevation levels (858, 1104, 1321 and 1547 m). Bird richness, diversity and evenness decreased with increasing altitude in both dry and wet seasons. Bird abundance declined with increasing elevation for the lower three elevation levels but peaked at the highest elevation. All diversity metrics were higher in the wet season compared to the dry season across all the years. Elevation had a greater effect on species assemblages than season, disturbance and temperature. Temperature had significant effects on abundance, diversity and richness, while disturbance had significant effects on diversity, evenness and richness. We conclude that bird assemblages in Mt. Kasigau are strongly shaped by elevational changes, while temperature and disturbance constitute important factors influencing bird conservation in the face of global warming. Our study highlights that elevation, disturbance and temperature influence bird assemblages along tropical elevational gradients.

Elevational patterns of microbial species richness and evenness across climatic zones and taxonomic scales.

Understanding the elevational patterns of soil microbial diversity is crucial for microbial biogeography, yet the elevational patterns of diversity across different climatic zones, trophic levels, and taxonomic levels remain unclear. In this study, we investigated the elevational patterns of species richness, species evenness and the relationship between species richness and evenness (RRE) in the forest soil bacterial and fungal communities and individual phyla across three climatic zones (tropical, subtropical, and cold temperate). Our results revealed that soil bacterial richness (alpha diversity) decreased with elevation, while fungal richness exhibited a hump-shaped pattern in the tropical and cold-temperate forests. Elevational patterns of evenness in bacterial and fungal communities showed the hump-shaped pattern across climatic zones, except for bacterial evenness in the tropical forest. Both bacterial and fungal richness and evenness were positively correlated in the subtropical and cold-temperate forests, while negatively correlated for bacteria in the tropical forest. The richness and evenness of soil microorganisms across different regions were controlled by climatic and edaphic factors. Soil pH was the most important factor associated with the variations in bacterial richness and evenness, while mean annual temperature explained the major variations in fungal richness. Our results addressed that the varieties of elevational patterns of microbial diversity in climatic zones and taxonomic levels, further indicating that richness and evenness may respond differently to environmental gradients.

The species richness and community composition of different growth forms and life forms of mosses are dominated by different factors along an elevational gradient of China

Understanding the elevational variation in species richness and community composition as well as their mechanisms is critical for biodiversity conservation. On Mt Jianfengling of China, we examined the elevational patterns of species richness and analyzed the important variables driving the variation of species richness and community composition using boosted regression trees for all mosses and two growth forms and three life forms of mosses, respectively. We assessed the contribution of elevation toward explaining the heterogeneity among sampling sites. Last, we compared the occurrence probability and proportional use of community type along the elevational gradient between two growth forms and three life forms of mosses. Although each taxonomic group displayed a negatively skewed (hump-shaped) diversity pattern and a high turnover rate of community composition along the elevational gradient, the leading drivers for the patterns of each group are different. The habitat complexity and the mid-domain effect (MDE) hypothesis were supported for the diversity patterns of acrocarpous mosses and turfs, whereas the habitat complexity hypothesis was supported for pleurocarpous mosses, mats, and wefts. Habitat composition dominated the community variation of acrocarpous mosses and turfs, whereas solar radiation was the leading factor for pleurocarpous mosses, mats and wefts. According to the additive diversity partitioning, α explained only 4.8–7.3% of the variation in species richness. For many low-lying sampling sites with sunny and dry conditions, extinction and dispersal limitation might be the primary processes producing low species richness pattern, which decreases the overall average diversity for each group. The variations of the occurrence probability and proportional use of community type along the elevational gradient in each group explain the contributions of elevation toward the heterogeneity among sampling sites for all mosses. With higher sensitivity to environmental changes, pleurocarpous mosses and wefts may have greater fluctuations in species richness when environmental conditions turn from unfavorable to optimal, therefore the elevation effect on explaining the heterogeneity among sampling sites was higher (18.9%) for pleurocarpous mosses as compared to 11.1% for acrocarpous mosses; and it ranged from a low of 11.0% in turfs to 19.9% in wefts. Although each group displayed similar biogeographic patterns along the elevational gradient, the underlying drivers are different. Therefore, the total measurements of species will veil the complex mechanisms for each growth form and life form. It is also suggested that conservation efforts should be paid to the top altitude for pleurocarpous mosses, mats and wefts, and the whole elevational range for acrocarpous mosses and turfs.

Elevational Patterns of Tree Species Richness and Forest Biomass on Two Subtropical Mountains in China

Increasing evidence shows that both abiotic and biotic factors affect species richness and stand biomass in forests, yet the relative and interactive impacts of these factors remain debated in different forest ecosystems. We sampled 55 forest plots (600 m2 per plot) on two subtropical mountains with distinct diversity levels in China to explore the elevational patterns of tree species richness and stand biomass and examined how they were affected by climate, stand structure, and dominance of mycorrhizal types. The tree species richness of both mountains decreased with elevation, while the stand biomass exhibited unimodal or no apparent trends. On both mountains, the tree species richness was strongly shaped by climatic factors, especially the mean annual temperature, whereas the stand biomass was mainly affected by the stand structure. Specifically, on the mountain with higher species richness, both the tree height variation and maximum tree size were strongly correlated with the stand biomass. Meanwhile, on the species-poor mountain with higher elevations, only the maximum tree size correlated with the stand biomass. The dominance of ectomycorrhizal trees also had positive effects on the stand biomass of both mountains. These results suggest that climate, stand structure, and mycorrhizal dominance may jointly drive the decoupling between tree species richness and stand biomass, which should be given more attention in further research and forest management to achieve the climate change mitigation goals.

Mechanisms behind elevational plant species richness patterns revealed by a trait‐based approach

AbstractAimsElevational patterns of plant species richness may be caused by multiple underlying mechanisms, and the same pattern can be predicted by different mechanisms. Using the steep elevational gradient of Tenerife as a model system, we aimed to test if the application of a trait‐based approach can help disentangle the role of potential mechanisms behind local elevational plant species richness patterns.LocationTenerife, Canary Islands, Spain.MethodsBased on vegetation relevés from natural vegetation and disturbed roadside habitat, along an elevational gradient of 2300 m, we observed a peak of plant species richness in the lowest third of the gradient. We considered three mechanisms potentially shaping this pattern: environmental filtering (temperature and precipitation), effects of area and disturbance. For these mechanisms, we hypothesized a distinct pattern of functional trait–elevation relationships. These were tested with in‐situ data of nine functional leaf traits, from which we calculated community‐weighted means (CWM) of traits and functional diversity (Rao's Q).ResultsWhile species richness was significantly positively correlated with temperature, area and disturbance, filtering through temperature was the only mechanism for which we could confirm most of our mechanism‐specific hypotheses about elevational trait changes: with increasing elevation, CWMs of most traits indicated shifts from acquisitive to conservative growth strategies, and functional diversity decreased. The shift of growth strategies also supported the disturbance effect, as we found overall more acquisitive communities at roadsides compared to natural habitats.ConclusionsOur results indicate that simple correlations between species richness and abiotic variables are not necessarily causal. Additional testing of mechanism‐specific hypotheses for elevational patterns of both CWMs and functional diversity can help distinguishing between correlational and mechanistic relationships between species richness and environmental variables. The trait‐based framework presented here can be fruitfully applied to better understand species richness patterns in other regions and across other types of environmental gradients.

Species richness and turnover patterns for tropical and temperate plants on the elevation gradient of the eastern Himalayan Mountains

Understanding species’ elevational distributions in mountain ecosystems is needed under climate change, but remote biodiverse mountain areas may be poorly documented. National Forest Inventories (NFIs) offer a potential source of data. We used NFI records from Bhutan to ask three questions about elevational richness patterns of Himalayan woody plant species. First, does the mean elevation for all species differ from those species whose entire elevational distribution is recorded in the survey? Second, how does the elevation of maximum richness differ when combining species originating from temperate and tropical regions vs. analyzing them separately? And third, do the highest species turnover rates adjoin elevation zones of maximum species richness? We used 32,198 species records from 1685 forest plots along a 7570 m gradient to map species elevation ranges. Species whose entire range was documented were those whose lowest records are located above 400 m, while bare rock defined all species’ upper limits. We calculated species richness and turnover using 400 m elevation bands. Of 569 species, 79% of temperate and 61% of tropical species’ elevation ranges were fully sampled within the NFI data. Mean elevation of tree and shrub species differed significantly for temperate and tropical species. Maximum combined species richness is from 1300 to 1700 m (277 species), differing significantly from maximum tropical (900–1300 m, 169) and temperate species richness (2500–2900 m, 92). Temperate tree turnover rate was highest in the bands adjoining its maximum species richness (2500–2900 m). But turnover for tropical trees was highest several bands above their maximum species richness, where turnover and decrease in richness interact. Shrub species turnover patterns are similar, but rates were generally higher than for trees. Bhutan’s NFI records show that woody plant species are arrayed on the Himalaya in part according to floristic origins, and that combining temperate- and tropical-originating floras for gradient-based studies such as species richness and turnover obscures actual elevational patterns. In addition, species whose ranges extend below the Himalayan elevation gradient should be accounted for in future studies that correlate climate and environment factors with elevational species richness patterns.

The Importance of Energy Theory in Shaping Elevational Species Richness Patterns in Plants.

Simple SummaryMountains are storehouses of global biodiversity; they host one-quarter of all terrestrial species at condensed spatial scales. Understanding the mechanisms and patterns that are associated with species richness along elevational gradients would help us to answer why mountains are so biologically diverse. However, despite decades of effort, a consensus regarding the processes that contribute to diversity in these locations is yet to be reached. Here, we compare the importance of four hypotheses on shaping the elevational species richness patterns of plants in 22 global mountainous regions. Moreover, a comparative analysis among different plant growth form groups was conducted to remove the influence of specific mountain attributes, such as topography complexity, history, and area. The results reveal that the performance of these hypotheses depend on the growth form and climatic conditions. The energy hypothesis provides a better explanation for the elevational species richness patterns of woody plants than the other hypotheses, while energy-related factors show greater explanatory power for predicting elevational species richness patterns in colder mountain regions. Our results highlight the importance of energy availability for the production of plant elevational species richness patterns, which is essential for the conservation and management of biodiversity.Many hypotheses have been proposed to explain elevational species richness patterns; however, evaluating their importance remains a challenge, as mountains that are nested within different biogeographic regions have different environmental attributes. Here, we conducted a comparative study for trees, shrubs, herbs, and ferns along the same elevational gradient for 22 mountains worldwide, examining the performance of hypotheses of energy, tolerance, climatic variability, and spatial area to explain the elevational species richness patterns for each plant group. Results show that for trees and shrubs, energy-related factors exhibit greater explanatory power than other factors, whereas the factors that are associated with climatic variability performed better in explaining the elevational species richness patterns of herbs and ferns. For colder mountains, energy-related factors emerged as the main drivers of woody species diversity, whereas in hotter and wetter ecosystems, temperature and precipitation were the most important predictors of species richness along elevational gradients. For herbs and ferns, the variation in species richness was less than that of woody species. These findings provide important evidence concerning the generality of the energy theory for explaining the elevational species richness pattern of plants, highlighting that the underlying mechanisms may change among different growth form groups and regions within which mountains are nested.

Elevational patterns in tropical bryophyte diversity differ among substrates: A case study on Baru volcano, Panama

AbstractQuestionsBryophytes attain their highest diversity in tropical mountain forests. Although distribution patterns have been described, little emphasis has been placed on comparing patterns among substrates (e.g., terrestrial, epiphytic). Understanding these patterns is important, because they determine not only the pool of genetic resources, but also the functioning of these forest ecosystems. Therefore, we studied how bryophyte species diversity changes with elevation, how elevational patterns differ between substrate types, and how elevational trends relate to environmental drivers.LocationBaru volcano, Panama.MethodsAt each of eight elevations, between 1900 and 3300 m, bryophytes were collected in 600‐cm2 plots from six substrate types with four replicates. Species cover was registered as a measure of relative abundance. Species richness and community structure were determined and related to elevation, substrate types, and environmental drivers at three scales (plots, sets of four replicate plots per substrate per elevation, and all plots at each elevation).ResultsBryophyte species richness decreased towards higher elevations, at all three scales and on all substrates except bryophytes on soil, for which, at the plot scale, richness peaked at higher elevations than on the other substrates. Relative humidity explained richness slightly better than elevation. Communities at the lowest elevations had the most uneven compositions, due to the presence of many small species with low abundance.ConclusionsIn studies on the spatial distribution of bryophyte diversity, it is essential to consider different substrates and spatial scales separately. If substrates differ in their elevational species richness patterns, climate and land‐use change may affect bryophyte diversity patterns not only directly, but also indirectly via changes in substrate availability. Therefore, a better understanding of the spatial variation in bryophyte diversity in mountains is essential to elucidate the effects of environmental change on this important group of plants and their implications for ecosystem functioning.

The influencing factors for distribution patterns of resident and migrant bird species richness along elevational gradients.

The latitudinal and elevational patterns of species richness of resident and migrant birds have been of interest to researchers over the past few decades, and various hypotheses have been proposed to explain the factors that may affect these patterns. This study aimed to shed light on the elevational distribution patterns of resident and migrant bird species richness by examining biotic and abiotic factors such as climate, and habitat heterogeneity using a piecewise structural equation model (pSEM). The overall pattern of resident species richness showed a decreasing trend with increasing elevation, whereas that of migrant species richness showed an increasing trend. The mid-peak pattern of species richness was affected by a combination of resident and migrant species and not by either resident or migrant species. Our results showed that resident species were distributed in lower elevation regions with higher mean spring temperatures, whereas migrant species were found in higher elevation regions with lower mean spring temperatures and higher overstory vegetation coverage. Although high elevation conditions might adversely affect the reproduction of migrant birds, higher overstory vegetation coverage at high elevations seemed to compensate for this by providing a better nesting and roosting environment. Despite the significance of habitat diversity and understory vegetation coverage in univariate linear regression models, multiple regression models of the interconnection of ecological processes demonstrated that mean spring temperature and overstory vegetation coverage were more explanatory than other variables.

Diversification and community assembly of the world’s largest tropical island

AbstractAimThe species diversity and endemism of tropical biotas are major contributors to global biodiversity, but the factors underlying the formation of these systems remain poorly understood.LocationThe world's largest tropical island, New Guinea.Time periodMiocene to present.Major taxa studiedPasserine birds.MethodsWe first generated a species‐level phylogeny of all native breeding passerine birds to analyse spatial and elevational patterns of species richness, species age and phylogenetic diversity. Second, we used an existing dataset on bill morphology to analyse spatial and elevational patterns of functional diversity.ResultsThe youngest New Guinean species are principally distributed in the lowlands and outlying mountain ranges, with the lowlands also maintaining the majority of non‐endemic species. In contrast, many species occurring in the central mountain range are phylogenetically distinct, range‐restricted, endemic lineages. Centres of accumulation for the oldest species are in montane forest, with these taxa having evolved unique bill forms in comparison to the remaining New Guinean species. For the morphological generalists, attaining a highland distribution does not necessarily represent the end to dispersal and diversification, because a number of new species have formed in the outlying mountain ranges, following recent colonization from the central range.Main conclusionsWe conclude that a general model of tropical montane diversification is that lineages commonly colonize the lowlands, shifting their ranges upslope through time to become range‐restricted montane forest endemics, attaining novel functional adaptations to these environments.

Think globally, measure locally: The MIREN standardized protocol for monitoring plant species distributions along elevation gradients.

Climate change and other global change drivers threaten plant diversity in mountains worldwide. A widely documented response to such environmental modifications is for plant species to change their elevational ranges. Range shifts are often idiosyncratic and difficult to generalize, partly due to variation in sampling methods. There is thus a need for a standardized monitoring strategy that can be applied across mountain regions to assess distribution changes and community turnover of native and non‐native plant species over space and time. Here, we present a conceptually intuitive and standardized protocol developed by the Mountain Invasion Research Network (MIREN) to systematically quantify global patterns of native and non‐native species distributions along elevation gradients and shifts arising from interactive effects of climate change and human disturbance. Usually repeated every five years, surveys consist of 20 sample sites located at equal elevation increments along three replicate roads per sampling region. At each site, three plots extend from the side of a mountain road into surrounding natural vegetation. The protocol has been successfully used in 18 regions worldwide from 2007 to present. Analyses of one point in time already generated some salient results, and revealed region‐specific elevational patterns of native plant species richness, but a globally consistent elevational decline in non‐native species richness. Non‐native plants were also more abundant directly adjacent to road edges, suggesting that disturbed roadsides serve as a vector for invasions into mountains. From the upcoming analyses of time series, even more exciting results can be expected, especially about range shifts. Implementing the protocol in more mountain regions globally would help to generate a more complete picture of how global change alters species distributions. This would inform conservation policy in mountain ecosystems, where some conservation policies remain poorly implemented.

A Small-Scale Analysis of Elevational Species Richness and Beta Diversity Patterns of Arthropods on an Oceanic Island (Terceira, Azores)

A Small-Scale Analysis of Elevational Species Richness and Beta Diversity Patterns of Arthropods on an Oceanic Island (Terceira, Azores)

A Small-Scale Analysis of Elevational Species Richness and Beta Diversity Patterns of Arthropods on an Oceanic Island (Terceira, Azores).

Simple SummaryWe studied the diversity of arthropods in native forests along a 1000 m elevation gradient on Terceira Island, Azores (Portugal). These forests form an isolated and threatened habitat with unique endemic species. We analysed the change in alpha and beta diversity of arthropod species with elevation and if the diversity of endemic, native non-endemic and introduced species responds differently to elevation. Resident arthropods were sampled using SLAM (Sea, Land and Air Malaise) traps between 2014 and 2018. Spiders (Araneae), beetles (Coleoptera), true bugs (Hemiptera) and barklice (Psocoptera), as well as endemic, native and introduced species, were analysed separately. Total species richness decreases with elevation for all species, Coleoptera and Psocoptera, and particularly so for introduced species, but peaks at mid-high elevation for Araneae and endemic species. These patterns are probably driven by unfavourable climatic conditions at higher elevations while being influenced by human disturbance at lower elevations. Total species diversity along the whole elevation gradient is shaped by this decreasing richness as well as the replacement of species at different elevations.We present an analysis of arthropod diversity patterns in native forest communities along the small elevation gradient (0–1021 m a.s.l.) of Terceira island, Azores (Portugal). We analysed (1) how the alpha diversity of Azorean arthropods responds to increasing elevation and (2) differs between endemic, native non-endemic and introduced (alien) species, and (3) the contributions of species replacement and richness difference to beta diversity. Arthropods were sampled using SLAM traps between 2014 and 2018. We analysed species richness indicators, the Hill series and beta diversity partitioning (species replacement and species richness differences). Selected orders (Araneae, Coleoptera, Hemiptera and Psocoptera) and endemic, native non-endemic and introduced species were analysed separately. Total species richness shows a monotonic decrease with elevation for all species and Coleoptera and Psocoptera, but peaks at mid-high elevation for Araneae and endemic species. Introduced species richness decreases strongly with elevation especially. These patterns are most likely driven by climatic factors but also influenced by human disturbance. Beta diversity is, for most groups, the main component of total (gamma) diversity along the gradient but shows no relation with elevation. It results from a combined effect of richness decrease with elevation and species replacement in groups with many narrow-ranged species.

Area modulates the effect of elevation but not of land use or canopy on tropical plant species richness

One of the few general patterns in ecology is the increase of species richness with area. However, factors driving species-area relationship (SAR) are under debate, and the role of human-induced changes has been overlooked so far. Furthermore, SAR studies in tropical regions, in particular in multilayered rain forests are scarce. On the other side, studies of global change-induced impacts on biodiversity have become increasingly important, particular in the tropics, where these impacts are especially pronounced. Here, we investigated if area modulates the effect of land use, elevation and canopy on plant species richness. For the first time we studied SAR in multilayered tropical forests considering all functional groups. We selected 13 natural and disturbed habitats on Kilimanjaro in Tanzania, distributed over an elevational range of 3700 m. In each habitat type, we set up three to six modified Whittaker plots. We recorded all plant species in 64 plots and 640 subplots and described SAR using the power function. Area consistently modulated effects of elevation on plant species richness, partly effects of land use but not effects of plant canopy. Thus, area needs to be taken into account when studying elevational plant species richness patterns. In contrast to temperate regions open and forest habitats did not differ in SAR, probably due to a distinct vertical vegetation zonation in tropical forests. Therefore, it is important to consider all vegetation layers including epiphytes when studying SAR in highly structured tropical regions.

The mid-domain effect and habitat complexity applied to elevational gradients: Moss species richness in a temperate semihumid monsoon climate mountain of China.

The utility of elevational gradients as tools to test either ecological hypotheses and delineate elevation‐associated environmental factors that explain the species diversity patterns is critical for moss species conservation. We examined the elevational patterns of species richness and evaluated the effects of spatial and environmental factors on moss species predicted a priori by alternative hypotheses, including mid‐domain effect (MDE), habitat complexity, energy, and environment proposed to explain the variation of diversity. Last, we assessed the contribution of elevation toward explaining the heterogeneity among sampling sites. We observed the hump‐shaped distribution pattern of species richness along elevational gradient. The MDE and the habitat complexity hypothesis were supported with MDE being the primary driver for richness patterns, whereas little support was found for the energy and the environmental factors.

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.

Disentangling the role of environment in cross-taxon congruence of species richness along elevational gradients

Spatial patterns of species richness have been found to be positively associated, a phenom called cross-taxon congruence. This may be explained by a common response to environment or by ecological interactions between taxa. Spatial changes in species richness are related to energy and environmental heterogeneity but their roles in cross-taxon congruence remain poorly explored. Elevational gradients provide a great opportunity to shed light on the underlying drivers of species richness patterns. We study the joint influence of environment and biotic interactions in shaping the cross-taxon congruence of plants and orthopterans species richness, along three elevational gradients in Sierras Grandes, central Argentina. Elevational patterns of species richness of orthopterans and plants were congruent, being temperature the best single predictor of both patterns supporting the energy-related hypotheses. Using a structural equation model, we found that temperature explained plant richness directly and orthopteran richness indirectly via orthopteran abundance. Cross-taxon congruence is likely due to a common response of both taxa to temperature although via different theoretical mechanisms, possibly, range limitations for plants and foraging activity for orthopterans. We disentangled the role of temperature in determining the cross-taxon congruence of plants and orthopterans by showing that a common response to the environment may mask different mechanisms driving the diversity of different taxonomic groups.

Elevational gradients of reptile richness in the southern Western Ghats of India: Evaluating spatial and bioclimatic drivers

AbstractExploring elevational patterns in species richness and their underlying mechanisms is a major goal in biogeography and community ecology. Reptiles can be powerful model organisms to examine biogeographical patterns. In this study, we examine the elevational patterns of reptile species richness and test a series of hypotheses that may explain them. We sampled reptile communities along a tropical elevational gradient (100–1,500 m a.s.l.) in the Western Ghats of India using time‐constrained visual encounter surveys at each 100‐m elevation zone for 3 years. First, we investigated species richness patterns across elevation and the support of mid‐domain effect and Rapoport's rule. Second, we tested whether a series of bioclimatic (temperature and tree density) and spatial (mid‐domain effect and area) hypotheses explained species richness. We used linear regression and AICc to compare competing models for all reptiles, and each of the subgroups: snakes, lizards, and Western Ghats’ endemics. Overall reptile richness and lizard richness both displayed linear declines with elevation, which was best explained by temperature. Snake richness and endemic species richness did not systematically vary across elevation, and none of the potential hypotheses explained variation in them. This is the first standardized sampling of reptiles along an elevational gradient in the Western Ghats, and our results agree with the global view that temperature is the primary driver of ectotherm species richness. By establishing strong reptile diversity–temperature associations across elevation, our study also has implications for the impact of future climate change on range‐restricted species in the Western Ghats.

The relationship between elevation and seed-plant species richness in the Mt. Namjagbarwa region (Eastern Himalayas) and its underlying determinants

Understanding how species richness changes along altitudinal gradients and what mechanisms answer for those patterns has intrigued increasing attention from numerous researchers, however, there is still no consistent agreement on these questions. Here, based on available distribution records, we explored the elevational pattern of species richness for seed plants in the Mt. Namjagbarwa region (Eastern Himalayas, China), a previously unexplored region. Species richness in each 100 m elevation band was estimated by spatial interpolation method according to their recorded elevation range over a large altitudinal gradient from 700 to 5000 m. In each elevation band, species richness was related to several explanatory factors, including temperature, humidity, spatially related variables and biogeographical distributions. Regression analyses were performed to obtain a quantitative assessment of the relative contribution of each predictor to the empirical richness pattern. Overall, species richness along elevation showed a hump-shaped pattern, with a peak at 1600–2000 m. In all sub-groups (life form, biogeographical affinity, and range-size category), species richness showed unimodal patterns with increasing elevation generally, but with different peak positions. Regression models indicated species richness patterns are highly correlated with energy-related factor in most data sets, explaining the observed richness patterns, but also more or less associated with other variables (climatic variation, area, precipitation, and mid-domain effect). The water-energy dynamics model was found to explain the elevational species richness patterns. Meantime, there was an elevational coincidence between maximum species richness and floristic overlap index, which proving the role of the biotic process in shaping the species richness gradient. Our findings reconfirmed that the elevational richness gradient is influenced by many processes, including ecological factors and evolutionary history, and suggested the need to consider more factors in order to determine key mechanisms in future studies.

Small mammal species richness and turnover along elevational gradient in Yulong Mountain, Yunnan, Southwest China.

Understanding the species diversity patterns along elevational gradients is critical for biodiversity conservation in mountainous regions. We examined the elevational patterns of species richness and turnover, and evaluated the effects of spatial and environmental factors on nonvolant small mammals (hereafter “small mammal”) predicted a priori by alternative hypotheses (mid‐domain effect [MDE], species–area relationship [SAR], energy, environmental stability, and habitat complexity]) proposed to explain the variation of diversity. We designed a standardized sampling scheme to trap small mammals at ten elevational bands across the entire elevational gradient on Yulong Mountain, southwest China. A total of 1,808 small mammals representing 23 species were trapped. We observed the hump‐shaped distribution pattern of the overall species richness along elevational gradient. Insectivores, rodents, large‐ranged species, and endemic species richness showed the general hump‐shaped pattern but peaked at different elevations, whereas the small‐ranged species and endemic species favored the decreasing richness pattern. The MDE and the energy hypothesis were supported, whereas little support was found for the SAR, the environmental stability hypothesis, and the habitat complexity. However, the primary driver(s) for richness patterns differed among the partitioning groups, with NDVI (the normalized difference vegetation index) and MDE being the most important variables for the total richness pattern. Species turnover for all small mammal groups increased with elevation, and it supported a decrease in community similarity with elevational distance. Our results emphasized for increased conservation efforts in the higher elevation regions of the Yulong Mountain.