What drives the species richness patterns of non‐volant small mammals along a subtropical elevational gradient?

The biodiversity of non‐volant small mammals along an extensive subtropical elevational gradient was studied for the first time on Gongga Mountain, the highest mountain in Hengduan Mountain ranges in China, located in one of the 25 global biodiversity hotspots. Non‐volant small mammals were replicate sampled in two seasons at eight sampling sites between 1000 and 4200 m elevation on the eastern slope of Gongga Mountain. In all, 726 individual small mammals representing 25 species were documented in 28 800 trap nights. The species richness pattern for non‐volant small mammals along the elevational gradients was hump‐shaped with highest richness at mid‐elevations. However, different richness patterns emerged between endemic and non‐endemic species, between larger‐ranged and smaller‐ranged species and between rodents and insectivores. Temperature, precipitation, plant species richness and geometric constraints (mid‐ domain effect) were most significant in explaining species richness patterns. Based on the analysis of simple ordinary least squares (OLS) and stepwise multiple regressions, the overall richness pattern, as well as the pattern of insectivores, endemic species and larger‐ranged species showed strong correlation with geometric constraint predictions. However, non‐endemic species richness was more strongly correlated with temperature, while rodent richness was correlated with plant species richness. Our study shows that no single key factor can explain all richness patterns of non‐volant small mammals. We need to be cautious in summarizing a general richness pattern of large species groups (e.g. small mammals or mammals) from species in smaller groups having different ecological distributions and life histories. Elevational richness patterns and their driving factors for small mammals are more likely dependent on what kind of species we study.     

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.     

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.     

面积、温度及分布区限制对物种丰富度海拔格局的影响: 以秦岭太白山为例

 物种丰富度的分布格局及其形成机制是生态学研究的热点。以往的研究主要描述丰富度的格局, 而对其形成机制研究较少, 且主要集中于探讨单个因子或过程的影响。物种丰富度同时受到多个因子和过程的综合作用, 面积、温度及物种分布区限制被认为是控制山地物种丰富度海拔格局的主要因素, 三者同时沿海拔梯度而变化, 同时作用于丰富度的海拔格局。幂函数种-面积关系(SAR)、生态学代谢理论(MTE)及中域效应假说(MDE)分别基于以上3个因素, 从机制上解释了物种丰富度 的海拔格局。探讨这些假说的相对影响对研究物种丰富度的大尺度格局及其形成机制具有重要意义。方差分离方法有利于分解不同因素的影响, 为此, 该文以秦岭太白山的植物物种丰富度为例, 采用方差分离和逐步回归方法, 分析了SAR、MTE及MDE对物种丰富度海拔格局的影响。结果表明, 太白山的植物物种丰富度沿海拔梯度呈单峰分布格局, 但丰富度峰值存在类群差异; 对太白山所有植物物种丰富度的垂直格局而言, SAR、MTE及MDE分别解释了其物种丰富度随海拔变化的66.4%、19.8%和37.9%, 共同解释了84.6%, 在消除其他因素的影响后, SAR和MTE的独立影响较高(分别为25.5%和17.7%), 而MDE的独立影响不显著; 分类群研究则发现, 苔藓植物丰富度的海拔格局主要受MDE的影响, 蕨类植物丰富度的海拔格局同时受到SAR、MTE以及MDE的影响, 而种子植物物种丰富度的海拔格局主要受SAR和MTE影响。     

The role of environment and mid-domain effect on moth species richness along a tropical elevational gradient

Aim The biodiversity of geometrid moths (Lepidoptera) along a complete tropical elevational gradient was studied for the first time. The patterns are described, and the role of geometric constraints and environmental factors is explored. Location The study was carried out along the Barva Transect (10° N, 84° W), a complete elevational gradient ranging from 40 to 2730 m a.s.l. in Braulio Carrillo National Park, Costa Rica, and adjacent areas. Methods Moths were sampled manually in 2003 and 2004 at 12 rain forest sites using light ‘towers’, each with two 15 W ultraviolet fluorescent tubes. We used abundance‐based rarefaction, statistical estimation of true richness (Chao 1), geographically interpolated observed richness and Fisher's alpha as measures of local diversity. Results A total of 13,765 specimens representing 739 species were analysed. All four measures showed a hump‐shaped pattern with maxima between 500 and 2100 m elevation. The two subfamilies showed richness and diversity maxima at either lower (Ennominae) or higher (Larentiinae) elevation than Geometridae as a whole. Among the four environmental factors tested, relative humidity yielded the highest correlation over the transect with the rarefaction‐based richness estimates as well as with estimated true species richness of Geometridae as a whole and of Larentiinae, while rainfall explained the greatest variation of Ennominae richness. The elevational pattern of moth richness was discordant with both temperature and with tree species richness. A combination of all environmental factors in a stepwise multiple regression produced high values of r² in Geometridae. The potential effects of geometric constraints (mid‐domain effect, MDE) were investigated by comparing them with observed, interpolated richness. Overall, models fitted very well for Geometridae as a whole and for Ennominae, but less well for Larentiinae. Small‐ranged species showed stronger deviations from model predictions than large‐ranged species, and differed strikingly between the two subfamilies, suggesting that environmental factors play a more pronounced role for small‐ranged species. We hypothesize that small‐ranged species (at least of the Ennominae) may tend to be host specialists, whereas large‐ranged species tend to be polyphagous. Based on interpolated ranges, mean elevational range for these moths was larger with increasing elevation, in accordance with Rapoport's elevational rule, although sampling effects may have exaggerated this pattern. The underlying mechanism remains unknown because Rapoport's ‘rescue’ hypothesis could not explain the observed pattern. Conclusions The results clearly show that moth diversity shows a hump‐shaped pattern. However, remarkable variation exists with regard to taxon and range size. Both environmental and geometric factors are likely to contribute to the observed patterns.     

Diversity and distribution of small mammals in the South American Dry Andes

The Andean mountain range has played an important role in the evolution of South American biota. However, there is little understanding of the patterns of species diversity across latitudinal and altitudinal gradients. In this paper, we examine the diversity of small mammals along the South Central Dry Andes (SCDA) within the framework of two contrasting hypotheses: (a) species richness decreases with increasing elevation and latitude; and (b) species richness peaks at altitudinal midpoints (mid‐domain). We explore the composition of the species pool, the impact of species–area relationships and the Rapoport effect (i.e. size of geographic ranges) along latitudinal and elevational gradients. First, we constructed a database of SCDA small mammals. Then, species richness patterns were analysed through generalized models, and species–area relationships were assessed by log–log regressions; the curvilinear method (c = S/Az) was use to compute richness corrected by area size. Lastly, the Rapoport effect was evaluated using the midpoint method. Our results show: (1) a richness of 67 small mammals along the SCDA, of which 36 are endemic; (2) a hump‐shaped pattern in species richness along elevation and latitudinal gradients; (3) a species–area relationship for both gradients; (4) endemic species corrected by area present a strong and positive relationship with elevation; (5) a Rapoport effect for the latitudinal ranges, but no effect across the elevational gradient; and (6) a major species turnover between 28° and 30° south latitude. This is the first study quantifying the diversity of small mammals encompassing the central Andean region. Overall, our macrogeographic analysis supports the previously postulated role of the Andes in the diversification of small mammals (i.e. in situ cladogenesis) and highlights some basic attributes (i.e. anatomy of geographic ranges; species–area relationships) when considering the consequences of climate change on biodiversity conservation of mountain ecosystems.     

Seasonal Change of Species Diversity Patterns of Non‐volant Small Mammals along Three Subtropical Elevational Gradients

Our understanding of geographic patterns of species diversity and the underlying mechanisms is increasing rapidly, whereas the temporal variation in these patterns remains poorly understood. We examined the seasonal species richness and species turnover patterns of non‐volant small mammals along three subtropical elevational gradients in southwest China. Small mammal diversity was surveyed in two seasons (early wet season and late wet season) using a standardized sampling protocol. The comparison of species richness patterns between two seasons indicated a temporal component in magnitude and shape, with species richness at high elevations clearly increased during the late wet season. Species richness demonstrated weak correlations with modelled temperature and precipitation. The elevational pattern of species turnover measured by Chao‐Sørenson similarity index also changed seasonally, even though the temporal pattern varied with scale. Species turnover between neighboring elevations at high elevations was slower in the late wet season. Meanwhile, there was an acceleration of species turnover along the whole range of the gradient. The seasonal change in species diversity patterns may be due to population‐level increases in abundance and elevational migration, whereas seasonal variation in factors other than temperature and precipitation may play a greater role in driving seasonal diversity patterns. Our study strongly supports the seasonality in elevational patterns of small mammal diversity in subtropical montane forests. Thus it is recommended that subsequent field surveys consider temporal sampling replicate for elevational diversity studies.     

What drives elevational patterns of diversity? A test of geometric constraints,climate and species pool effects for pteridophytes on an elevational gradient in Costa Rica

Aim We studied pteridophyte species richness between 100 m and 3400 m along a Neotropical elevational gradient and tested competing hypotheses for patterns of species richness. Location Elevational transects were situated at Volcán Barva in the Braulio Carrillo National Park and La Selva Biological Station (100–2800 m) and Cerro de la Muerte (2700–3400 m), both on the Atlantic slope of Costa Rica, Central America. Method We analysed species richness on 156 plots of 20 × 20 m and measured temperature and humidity at four elevations (40, 650, 1800 and 2800 m). Species richness patterns were regressed against climatic variables (temperature, humidity, precipitation and actual evapotranspiration), regional species pool, area and predicted species number of a geometric null model (the mid‐domain effect, MDE). Results The species richness of the 484 recorded species showed a hump‐shaped pattern with elevation with a richness peak at mid‐elevations (c. 1700 m). The MDE was the single most powerful explanatory variable in linear regression models, but species richness was also associated strongly with climatic variables, especially humidity and temperature. Area and species pool were associated less strongly with observed richness patterns. Main conclusions Geometric models and climatic models exclusive of geometric constraints explained comparable amounts of the elevational variation in species richness. Discrimination between these two factor complexes is not possible based on model fits. While overall fits of geometric models were high, large‐ and small‐ranged species were explained by geometric models to different extents. Species with narrow elevational ranges clustered at both ends of the gradient to a greater extent than predicted by the MDE null models used here. While geometric models explained much of the pattern in species richness, we cannot rule out the role of climatic factors (or vice versa) because the predicted peak in richness from geometric models, the empirical peak in richness and the overlap in favourable environmental conditions all coincide at middle elevations. Mid‐elevations offer highest humidity and moderate temperatures, whereas at high elevations richness is reduced due to low temperatures, and at low elevations by reduced water availability due to high temperatures.     

秦岭南坡陕西洋县辖区哺乳动物物种多样性的空间分布格局

物种多样性的空间分布格局一直是生态学和生物地理学研究的一个热点问题。山地生态系统的生境异质性和物种多样性高, 适合研究物种多样性空间分布格局及其相关机制。2016年11月至2017年11月, 本研究选取秦岭南坡陕西洋县辖区作为研究区域, 采用样线法、红外相机法和笼捕/夹捕法, 系统分析了8目21科48种哺乳动物物种多样性的空间分布格局。研究结果发现秦岭南坡洋县辖区哺乳动物物种丰富度的空间分布格局大致是中南部低, 北部和东部高; 物种多样性指数大致是中南部和北部低, 东部高。啮齿类动物和非啮齿类动物的空间分布格局存在差异。哺乳动物物种丰富度和多样性指数的垂直分布格局都符合中峰模式, 但啮齿类动物和非啮齿类动物间存在差异。最优线性模型结果表明, 研究地区哺乳动物物种多样性的空间分布格局受到多种环境因素的共同影响。其中, 年均温与物种多样性的相关性最强, 在6个最优线性模型中贡献都是最大。综上, 秦岭南坡洋县辖区中高海拔区域的物种多样性较高, 应加强对中高海拔地区的保护, 以维系该区域较高的生物多样性。     

Orchid Species Richness along Elevational and Environmental Gradients in Yunnan,China

The family Orchidaceae is not only one of the most diverse families of flowering plants, but also one of the most endangered plant taxa. Therefore, understanding how its species richness varies along geographical and environmental gradients is essential for conservation efforts. However, such knowledge is rarely available, especially on a large scale. We used a database extracted from herbarium records to investigate the relationships between orchid species richness and elevation, and to examine how elevational diversity in Yunnan Province, China, might be explained by mid-domain effect (MDE), species–area relationship (SAR), water–energy dynamics (WED), Rapoport’s Rule, and climatic variables. This particular location was selected because it is one of the primary centers of distribution for orchids. We recorded 691 species that span 127 genera and account for 88.59% of all confirmed orchid species in Yunnan. Species richness, estimated at 200-m intervals along a slope, was closely correlated with elevation, peaking at 1395 to 1723 m. The elevational pattern of orchid richness was considerably shaped by MDE, SAR, WED, and climate. Among those four predictors, climate was the strongest while MDE was the weakest for predicting the elevational pattern of orchid richness. Species richness showed parabolic responses to mean annual temperature (MAT) and mean annual precipitation (MAP), with maximum richness values recorded at 13.7 to 17.7°C for MAT and 1237 to 1414 mm for MAP. Rapoport’s Rule also helped to explain the elevational pattern of species richness in Yunnan, but those influences were not entirely uniform across all methods. These results suggested that the elevational pattern of orchid species richness in Yunnan is collectively shaped by several mechanisms related to geometric constraints, size of the land area, and environments. Because of the dominant role of climate in determining orchid richness, our findings may contribute to a better understanding of the potential effects of climate change on orchid diversity, and the development of conservation strategies for orchids.     

Elevational gradients and species richness: do methods change pattern perception?

Aim Species richness patterns along elevational gradients have been documented extensively. Yet, the implications of differences in how the data are compiled are seldom explored. We investigate the effect of grain size on the richness–elevation relationship. Grain size varies among the principal methods used to collect or aggregate species occurrences: localized sites, elevational ‘bins’ and interpolation of species ranges. Assumptions of sampling and species distributions also vary among these methods. Methodology can influence the pattern that is perceived and comparability of results. We compare patterns from all three methods explicitly using the same suite of observations, based on museum records and field surveys of non‐flying small mammals. Our assessment is enhanced by comparing patterns resulting from each method for each of six adjacent mountain ranges. Location Utah, North America. Methods We document elevational species richness patterns using generalized linear models (GLMs), comparing the general shape of the trend as well as curvature, location and magnitude of peak richness across methods, both within and among gradients. We also introduce a new procedure to test for richness peaks using site‐based occurrences. Results We find a general congruence of the richness–elevation relationship, depicting a hump‐shaped pattern with a second‐order polynomial GLM showing a significant fit to nearly all gradient‐methodology combinations. However, underlying characteristics of the trend may vary with grain size. As grain size coarsens, maximum species richness increases and elevation of the mode slightly decreases. Results for curvature vary, but degree of curvature tends to increase as grain size coarsens. The richness–elevation patterns are independent of sampling effects. Main conclusions The perceived elevational diversity pattern for small mammals along these mountain ranges is not scale‐dependent. Differences in how the data are compiled are not reflected in major differences in patterns, even when local samples are neither uniformly spaced nor sampled with the same intensity. This result lends confidence to the assertion that patterns documented in similar studies with different methodologies and for which sampling is sufficiently comprehensive are good indicators of diversity. However, consistency of results from more than one compilation method may help to address issues of scale‐dependence, more so when these comparisons are made explicit.     

Elevational diversity patterns of small mammals on Mount Kinabalu, Sabah, Malaysia

1 Diversity patterns of small mammals were studied along an elevational transect on Mount Kinabalu, the highest mountain in South‐east Asia, utilizing data from previously existing sources and a new field study. A mark‐and‐release study (conducted during wet and dry seasons between November 1994 and April 1995) resulted in captures of 12 small mammal species, including two species of squirrels, two tree shrews, seven murid rodents and one gymnure. 2 Based on data compiled from this survey, museum specimens, and published and unpublished literature (analysed by locally weighted sums of squares and quadratic polynomial regressions), species richness of small mammals formed a middle elevation bulge, highest at about 1200–1400 m and declining at lower and higher elevations. Trapping during two seasons did not change the assessment of the pattern. 3 A cluster analysis of these data indicated that there are two elevationally associated faunas, one in the highlands and another in the lowlands. The transition between these two assemblages is at 1700–1800 m elevation. The lowland faunal assemblage has the highest number of species, with maximum species richness at about 1300 m for total small mammal species, about 1200 m for arboreal species and about 1400 m for terrestrial species. 4 The areas where much overlapping of species occurs are the elevations where climate and vegetation change rapidly from lowland to montane types. Tree species, gymnosperms, orchids and ferns showed a similar curvilinear pattern along the same elevational gradient, with maximum species richness at about 1400–1500 m. Temperature declined progressively with increasing elevation, but rainfall and humidity reached their highest levels at about 1700 m. 5 Maximum diversity of small mammals thus occurred at the elevation where a highland and a lowland assemblage overlapped, where several types of plants reached their maximum diversity, and where rainfall and humidity reached their maxima. Similar patterns have been documented for small mammals, plants, and climate at sites scattered in Indo‐Australia from Taiwan to New Guinea.     

Neutral community dynamics, the mid-domain effect and spatial patterns in species richness

The mid‐domain effect (MDE) aims to explain spatial patterns in species richness invoking only stochasticity and geometrical constraints. In this paper, we used simulations to show that its main qualitative prediction, a hump‐shaped pattern in species richness, converges to the expectation of a spatially bounded neutral model when communities are linked by short‐distance migration. As these two models can be linked under specific situations, neutral theory may provide a mechanistic population level basis for MDE. This link also allows establishing in which situations MDE patterns are more likely to be found. Also, in this situation, MDE models could be used as a first approximation to understand the role of both stochastic (ecological drift and migration) and deterministic (adaptation to environmental conditions) processes driving the spatial structure of species richness.     

Elevational gradients of small mammal diversity on the northern slopes of Mt. Qilian, China

Aim Small mammal species richness and relative abundance vary along elevational gradients, but there are different patterns that exist. This study reports the patterns of distribution and abundance of small mammals along the broader elevational gradient of Mt. Qilian range. Location The study was conducted in the Mt. Qilian range, north‐western China, from June to August 2001. Methods Removal trapping was conducted using a standardized technique at 7 sites ranging between 1600 and 3900 m elevation within three transects. Correlation, regression and graphical analyses were used to evaluate the diversity patterns along this elevational gradient. Results In total, 586 individuals representing 18 nonvolant small mammal species were collected during 20 160 trap nights. Species composition was different among the three transects with 6 (33%) of the species found only within one transect. Elevational distribution and relative abundance of small rodents showed substantial spatial variation, with only 2 species showing nonsignificant capture frequencies across elevations. Despite these variations, some general patterns of elevational distribution emerged: humped‐shape relationships between species diversity and elevation were noted in all three transects with diversity peaks at middle elevations. In addition, relative abundance was negatively correlated with elevation. Conclusions Results indicate that maximum richness and diversity of nonvolant small mammals occurred at mid‐elevations where several types of plants reached their maximum diversity and primary productivity, and where rainfall and humidity reached a maximum. It is demonstrated that the mid‐elevation bulge is a general feature of at least a large portion of the biota on the Mt. Qilian range.     

The species richness pattern of vascular plants along a tropical elevational gradient and the test of elevational Rapoport's rule depend on different life‐forms and phytogeographic affinities

The research about species richness pattern and elevational Rapoport's rule (ERR) have been carried out mostly in the temperate regions in the recent years and scarcely in the tropical mountains; meanwhile, it is unclear whether the ERR is consistent among different life‐forms and phytogeographic affinities. Here, we compiled a database of plant species of Mount Kenya, a tropical mountain of East Africa, and divided these species into twelve groups depending on the life‐form and phytogeographic affinity of each species. We inspected the species richness pattern of each group along the elevation gradient and also tested ERR of each group using Stevens' method. Our results showed that species richness of the total species showed a positively skewed (hump‐shaped) pattern along the elevation gradient and different life‐forms and phytogeographic affinities showed similar hump‐shaped patterns as the total species. The average elevation range size of the total species and herbaceous species showed increasing patterns along the elevation gradient, while lycophytes and ferns, and woody species showed an obvious downward trend after peaking in the high elevation regions. We concluded that the widely distributed herbaceous species which also have broad elevation range sizes are more applicable to ERR, while the narrowly distributed woody species with small elevation range sizes occurring in the higher elevations could reverse ERR. Therefore, we concluded that the ERR is not consistent among different organisms in the same region.     

Exploring anthropogenic and natural processes shaping fern species richness along elevational gradients

Aim (1) To explore the impact of land use, climate and environmental heterogeneity on fern species richness along a complete elevational gradient, and (2) to evaluate the relative importance of the three groups of variables within different elevational intervals. Location A temperate mountain region (55,507 km²) of Italy on the southern border of the European Alps divided into a regular grid of 1476 cells (grain 35.7 km²). Methods We applied multiple regression (spatial and non‐spatial) to determine the relative influence of the three groups of variables on species richness, including variation partitioning at two scales. We considered the whole gradient (all 1476 cells) to explain the overall elevational pattern of species richness, and we grouped the cells into elevational intervals of 500 m in order to evaluate the explanatory power of the predictors within different zones along the gradient. Results Species richness showed a hump‐shaped pattern with elevation, forming a plateau between 800 and 1500 m. The lowest species richness was found in warm and relatively dry disturbed lowlands. Moving upwards, the greatest species richness was found in forest‐dominated mid‐elevations with high environmental heterogeneity. At high elevations dominated by open natural habitats, where temperature and precipitation were relatively low, species richness declined but less sharply than in the lowlands. Although it was impossible to separate the effects of the three groups of predictors along the whole gradient, the analysis of separate elevational intervals shed light on their relative importance. The decline of species richness within lowlands was mainly related to a combined effect of deforestation and low environmental heterogeneity. In the middle part of the gradient, habitat heterogeneity and topographic roughness were positively associated with species richness. The richness decline within high‐elevation areas was related mostly to climatic constraints. Main conclusions Human impact due to land‐use modifications strongly affects the elevational pattern of species richness. It is therefore increasingly important to adopt a multiple‐hypothesis approach, taking anthropogenic effects explicitly into account when describing ecological processes along elevational gradients.     

Disentangling the effects of available area,mid-domain constraints,and species environmental tolerance on the altitudinal distribution of tenebrionid beetles in a Mediterranean area

Most studies have attempted to identify the major environmental factors responsible for elevational variations in species richness. Such studies have been mainly performed in temperate and tropical areas, whereas the mediterranean biome has been substantially neglected. The aim of this paper was to disentangle the effects of available area, mid-domain constraints, and the environmental tolerance of species, on the altitudinal distribution of tenebrionid beetles in a Mediterranean region. A comprehensive faunistic database was used to assess the elevational distribution of tenebrionids in Latium (Central Italy). Variations in species richness, beta diversity and nestedness were analysed in association with variation in species ranges and midpoints. Variation in species richness was contrasted with patterns expected on the basis of the mid domain effect (MDE) and available surface area. After correcting for differences in area availability due to the conical shape of mountains, an unexpected triphasic pattern emerged: (1) at low altitudes, species richness was higher than expected on the basis of the effect of area and the MDE; (2) at around 800 m elevation, there is an abrupt change in species assemblages, and richness values fit those predicted by the MDE; (3) a new dramatic change occurred at 1,700 m, with tenebrionid assemblages composed of a small number of mainly eurytopic species. The integrated approach used in this study demonstrates that neither MDE nor monotonic patterns fully explain the observed diversity patterns. Variations in species ranges indicate that the elevational gradient filters species according to their ecological tolerance.     

Elevational gradient analyses and the use of historical museum specimens: a cautionary tale

Aim The value of biodiversity informatics rests upon the capacity to assess data quality. Yet as these methods have developed, investigating the quality of the underlying specimen data has largely been neglected. Using an exceptionally large, densely sampled specimen data set for non‐flying small mammals of Utah, I evaluate measures of uncertainty associated with georeferenced localities and illustrate the implications of uncritical incorporation of data in the analysis of patterns of species richness and species range overlap along elevational gradients. Location Utah, USA, with emphasis on the Uinta Mountains. Methods Employing georeferenced specimen data from the Mammal Networked Information System (MaNIS), I converted estimates of areal uncertainty into elevational uncertainty using a geographic information system (GIS). Examining patterns in both areal and elevational uncertainty measures, I develop criteria for including localities in analyses along elevational gradients. Using the Uinta Mountains as a test case, I then examine patterns in species richness and species range overlap along an elevational gradient, with and without accounting for data quality. Results Using a GIS, I provide a framework for post‐hoc 3‐dimensional georeferencing and demonstrate collector‐recorded elevations as a valuable technique for detecting potential errors in georeferencing. The criteria established for evaluating data quality when analysing patterns of species richness and species range overlap in the Uinta Mountains test case reduced the number of localities by 44% and the number of associated specimens by 22%. Decreasing the sample size in this manner resulted in the subsequent removal of one species from the analysis. With and without accounting for data quality, the pattern of species richness along the elevational gradient was hump‐shaped with a peak in richness at about mid‐elevation, between 2300 and 2600 m. In contrast, the frequencies of different pair‐wise patterns of elevational range overlap among species differed significantly when data quality was and was not accounted for. Main conclusions These results indicate that failing to assess spatial error in data quality did not alter the shape of the observed pattern in species richness along the elevational gradient nor the pattern of species’ first and last elevational occurrences. However, it did yield misleading estimates of species richness and community composition within a given elevational interval, as well as patterns of elevational range overlap among species. Patterns of range overlap among species are often used to infer processes underlying species distributions, suggesting that failure to account for data quality may alter interpretations of process as well as perceived patterns of distribution. These results illustrate that evaluating the quality of the underlying specimen data is a necessary component of analyses incorporating biodiversity informatics.     

Terrestrial gastropod diversity in an alpine region: disentangling effects of elevation,area, geometric constraints,habitat type and land‐use intensity

Elevational gradients have proven to be useful to examine key factors shaping species diversity patterns. This study examines the effects of elevation, area, geometric constraints, habitat type, environmental factors and land‐use intensity on terrestrial gastropod diversity patterns in Val Müstair, an alpine region influenced by different types of agricultural land use in the eastern Alps, Switzerland. Gastropods were sampled using a standardized method in 180 sites spanning an elevational range from 1215 to 2770 m and covering 11 different habitat types. A total of 11 102 specimens representing 70 species were recorded. Observed species richness, statistically estimated true richness (Chao) and geographically interpolated observed richness were used as measures of local species richness. The comparison of three alternative models (environmental, geometric constraints and gastropod abundance models) revealed that the environmental model explained most of the variation in all measures of local diversity. The best model combining the predictors of all three models showed that elevation, soil pH and habitat type affected all measures of local species richness. Similar analyses conducted at the level of 150‐m elevational bands showed that elevation was again the best predictor of species richness, while the area of the elevational band did not have any influence. However, in one out of the two measures of band species richness, the best model indicated that geometric constraints may also contribute to the observed pattern. At both spatial scales, all measures of species richness decreased with increasing elevation. An analysis of species‐specific life‐history traits showed that adult shell size of land snails decreased with increasing elevation. Most species with large shells were confined to lower elevations. The results indicate that environmental factors might be most important in shaping the observed patterns.