The impact of sterile populations on the perception of elevational richness patterns in ferns

Dispersal may influence the spatial distribution of species richness through mass or source‐sink effects, but the extent of sink populations at the community level remains largely unknown due to difficulties of identifying such populations. We compared the richness patterns of ferns in 333 plots along six tropical elevational gradients in America, the Mascarenes, and southeast Asia, using sterile populations as an indication of sink populations. First, we tested whether sterile fern records were more common towards the elevational range limits of the individual species, but found this pattern in only one out of ten cases. It is therefore uncertain if sterile records correspond to marginal sink populations. Second, we compared the elevational richness patterns of sterile and fertile species. In several cases, elevational trends for sterile and fertile records were quite similar, but in others they differed distinctly. The percentage of sterile records per plot decreased with elevation among epiphytic ferns along all six transects, whereas terrestrials showed mixed results (decrease, increase, and U‐shaped patterns). The percentage of sterile species records per plot relative to the number of species per plot recovered four significant patterns among the twelve cases analysed: higher percentages at higher species numbers among terrestrial ferns on two transects and lower percentages among epiphytes on two others. Despite the problems with equating sterile records to sink populations, we thus found distinct elevational patterns of sterile records that clearly affected our perception of the overall richness patterns. Ignoring the impact of population dynamics on diversity patterns is thus liable to result in misinterpretations of the diversity patterns.     

A comparison of altitudinal species richness patterns of bryophytes with other plant groups in Nepal, Central Himalaya

Aim To explore species richness patterns in liverworts and mosses along a central Himalayan altitudinal gradient in Nepal (100–5500 m a.s.l.) and to compare these patterns with patterns observed for ferns and flowering plants. We also evaluate the potential importance of Rapoport’s elevational rule in explaining the observed richness patterns for liverworts and mosses. Location Nepal, Central Himalaya. Methods We used published data on the altitudinal ranges of over 840 Nepalese mosses and liverworts to interpolate presence between maximum and minimum recorded elevations, thereby giving estimates of species richness for 100‐m altitudinal bands. These were compared with previously published patterns for ferns and flowering plants, derived in the same way. Rapoport’s elevational rule was assessed by correlation analyses and the statistical significance of the observed correlations was evaluated by Monte Carlo simulations. Results There are strong correlations between richness of the four groups of plants. A humped, unimodal relationship between species richness and altitude was observed for both liverworts and mosses, with maximum richness at 2800 m and 2500 m, respectively. These peaks contrast with the richness peak of ferns at 1900 m and of vascular plants, which have a plateau in species richness between 1500 and 2500 m. Endemic liverworts have their maximum richness at 3300 m, whereas non‐endemic liverworts show their maximum richness at 2700 m. The proportion of endemic species is highest at about 4250 m. There is no support from Nepalese mosses for Rapoport’s elevational rule. Despite a high correlation between altitude and elevational range for Nepalese liverworts, results from null simulation models suggest that no clear conclusions can be made about whether liverworts support Rapoport’s elevational rule. Main conclusions Different demands for climatic variables such as available energy and water may be the main reason for the differences between the observed patterns for the four plant groups. The mid‐domain effect may explain part of the observed pattern in moss and liverwort richness but it probably only works as a modifier of the main underlying relationship between climate and species richness.     

Effects of altitude and climate in determining elevational plant species richness patterns: A case study from Los Tuxtlas,Mexico

Altitudinal changes of composition and richness of montane plant assemblages are complex, depending on the taxonomic group and gradient conditions, with different factors involved that are directly altitude-dependent (e.g., temperatures, air pressure) and altitude-independent (e.g., precipitation, cloud cover, area). In order to assess the relative impacts of temperature, precipitation, air humidity, and area of altitudinal belts on plant diversity, we analyzed diversity patterns of five species-rich groups, mostly herbaceous plants, in 74 forest plots along three climatically contrasting elevational transects from humid tropical lowland vegetation up to cloud forests at Los Tuxtlas, Mexico. We recorded 278 plant species, with ferns being the most species-rich group followed by orchids, bromeliads, aroids, and piperoids. The most striking results were the contrasting patterns and model results for terrestrial and epiphytic taxa. Whereas the richness of all terrestrial species taken together did not change significantly with elevation, vascular epiphytes showed increasing species numbers with altitude. However, a number of individual terrestrial taxa showed also significant elevation-related changes: aroids showed a marked decline with hight, orchids and piperoids increased, and ferns displayed a hump-shaped pattern with highest richness in mid-altitudes. Among the epiphytes, aroids declined while most other groups increased with altitude. This distinction is relevant for projections of responses of plant communities to climate change, which will lead to increased temperatures and to changing precipitation and cloud condensation regimes and thus will likely affect terrestrial and epiphytic species in different ways.     

Constant tree species richness along an elevational gradient of Mt. Bokor,a table-shaped mountain in southwestern Cambodia

Some previous studies along an elevational gradient on a tropical mountain documented that plant species richness decreases with increasing elevation. However, most of studies did not attempt to standardize the amount of sampling effort. In this paper, we employed a standardized sampling effort to study tree species richness along an elevational gradient on Mt. Bokor, a table-shaped mountain in southwestern Cambodia, and examined relationships between tree species richness and environmental factors. We used two methods to record tree species richness: first, we recorded trees taller than 4 m in 20 uniform plots (5 × 100 m) placed at 266–1048-m elevation; and second, we collected specimens along an elevational gradient from 200 to 1048 m. For both datasets, we applied rarefaction and a Chao1 estimator to standardize the sampling efforts. A generalized linear model (GLM) was used to test the relationship of species richness with elevation. We recorded 308 tree species from 20 plots and 389 tree species from the general collections. Species richness observed in 20 plots had a weak but non-significant correlation with elevation. Species richness estimated by rarefaction or Chao1 from both data sets also showed no significant correlations with elevation. Unlike many previous studies, tree species richness was nearly constant along the elevational gradient of Mt. Bokor where temperature and precipitation are expected to vary. We suggest that the table-shaped landscape of Mt. Bokor, where elevational interval areas do not significantly change between 200 and 900 m, may be a determinant of this constant species richness.     

Spatial patterns of plant richness across treeline ecotones in the Pyrenees reveal different locations for richness and tree cover boundaries

Aim  To forecast the responses of alpine flora to the expected upward shift of treeline ecotones due to climatic warming, we investigated species richness patterns of vascular plants at small spatial scales across elevational transects.
Location  Richness patterns were assessed at local scales along the elevational gradient in two undisturbed treeline ecotones and one disturbed treeline ecotone in the Spanish Pyrenees.
Methods  We placed a rectangular plot (0.3–0.4 ha) in each treeline ecotone. We estimated and described the spatial patterns of plant richness using the point method and Moran's I correlograms. We delineated boundaries based on plant richness and tree cover using moving split windows and wavelet analysis. Then, to determine if floristic and tree cover boundaries were spatially related, overlap statistics were used.
Results  Plant richness increased above the forest limit and was negatively related to tree cover in the undisturbed sites. The mean size of richness patches in one of these sites was 10–15 m. Moving split windows and wavelets detected the sharpest changes in plant richness above the forest limit at both undisturbed sites. Most tree cover and plant richness boundaries were not spatially related.
Main conclusions  The upslope decrease of tree cover may explain the increase of plant richness across alpine treeline ecotones. However, the detection of abrupt richness boundaries well above the forest limit indicates the importance of local environmental heterogeneity to explain the patterns of plant richness at smaller scales. We found highly diverse microsites dominated by alpine species above the forest limit, which should be monitored to describe their response to the predicted upward shift of forests.     

Elevational patterns of fern species assemblages and richness in central Japan

We conducted field surveys in 807 quadrats to evaluate the elevational belts, boundary and richness patterns of ferns and lycophytes in the temperate region of central Japan. We analysed fern species assemblages at 100 m elevational steps by cluster analysis and tested the number of upper and lower boundaries for elevational intervals against a null model of random distribution of elevational limits. We compared the pattern of fern species richness along the elevational gradients in central Japan with patterns in several locations to evaluate the fern flora in central Japan in relation to the rest of the world. We recorded 261 ferns species in total, which is one-third of the Japanese ferns. We found clear elevational boundaries of fern assemblages at 900 and 1,800 m and three fern elevational zones, which corresponded well to the elevational limits of forest types in central Japan. The pattern of fern species richness in central Japan was an asymmetric hump-shaped pattern that peaked close to the sea level, with the peak of local richness at lower elevations than that of regional richness. We found that the peak of fern species richness along the elevational gradient in Japan was located at lower elevations than that of fern elevational patterns in several locations around the world.     

Elevation‐richness pattern of vascular plants in wadis of the arid mountain Gebel Elba,Egypt

Mountains provide a unique opportunity to study drivers of species richness across relatively short elevation gradients. However, few studies have reported elevational patterns for arid mountains. We studied elevation‐richness pattern along an elevational gradient at the arid mountain Gebel Elba, south‐east of Egypt, expecting a unimodal richness pattern. We sampled 133 vegetation plots (10 × 10 m) in four wadis along an elevational gradient from 130 to 680 m which represents the transition from desert to mountain wadi systems. We used generalised additive models to describe the relationship between elevation and plant species richness. We found a strong increase in species richness and Shannon diversity at low elevations followed by a plateau at mid‐ to high elevations. When we analysed each tributary as a single gradient, no pattern was found. The analysed elevational gradient seems to be a major stress gradient in terms of temperature and water availability, exhibiting a trend of increasing species richness that changes to a plateau pattern; a pattern rarely observed for wadi systems in arid mountains. We discuss the observed pattern with the climatic stress hypothesis and the environmental heterogeneity hypothesis as possible explanations for the pattern.     

Regional and Elevational Patterns in Vascular Epiphyte Richness on an East Asian Island

The distribution of species on mountains has been related to various predictor variables, especially temperature. Thermal specialization—presumed to be more pronounced on tropical mountains than on temperate mountains—accounts for the elevational pattern of species richness and varies between organisms and geographic areas. In this study, the elevational and regional distribution patterns of 331 epiphyte species in Taiwan were explored using 39,084 botanic collections, mostly from herbaria. Species richness showed a peak in elevation at 500–1500 m. This peak could not be explained by a null model, the mid‐domain effect, suggesting that environmental variables accounted mostly for the distribution of species on the mountains. Next, species distributions were modeled to assess epiphyte regional and elevational distribution patterns. The model results not only corroborated the position of the mid‐elevation peak in richness, but also identified two mountain areas on the island with exceptionally high species richness. These areas of high epiphyte diversity coincide with areas of high rainfall in relation to the direction of the prevailing winds. Moreover, a subsequent exploratory ordination analysis showed a varied thermal preference between epiphyte subcategories (hemiepiphytes, dicotyledons, orchids, and ferns). In contrast to predictions by the elevational Rapoport's rule, ordination analysis also showed that the degree of thermal specialization increased with elevation, suggesting that highland species may be especially vulnerable to global warming.     

A human-induced downward-skewed elevational abundance distribution of pteridophytes in the Bolivian Andes

Aim  To search for differences in the spatial variability of upper and lower elevational distribution limits of tropical ferns, based on the assumption that these are determined to different degrees by biotic and abiotic factors.
Location  The Yungas biogeographical region, in the Bolivian Andes.
Methods  From a data base of > 25,000 herbarium records, we analysed the skewness of the elevational distribution of 220 montane pteridophyte species, each with  15 records. Additionally, we compared the spatial variability of upper and lower elevational range limits of ferns in 351 plots of 400 m² each along four elevational transects separated by 15–450 km.
Results  Individual species showed variable elevational distribution patterns, ranging from symmetric to asymmetric, i.e. downward and upward skewed, but overall there was a statistically significant trend towards asymmetric distributions with abrupt upper limits and diffuse lower limits. This trend, however, was almost exclusively due to terrestrial species occurring at and above the current timberline. The analysis of the elevational transects revealed no significant trends.
Main conclusions  The downward-skewed distributional abundance of terrestrial, open-country ferns near the timberline appears to be a result of the extensive forest destruction that has lowered the timberline in the high Andes by 500–800 m, opening up habitats for a restricted suite of species. Our study shows that a limited number of species can cause a general trend in the overall data set, and that failure to extract these data may result in unsupported conclusions, in our case to assign a greater importance to biotic and abiotic factors in the elevational limitation of plants at lower and upper elevations, respectively.     

Altitudinal patterns of seed plant richness in the Gaoligong Mountains, south-east Tibet, China

Elevational patterns of species richness and their underlying mechanisms have long been a controversial issue in biodiversity and biogeographical research, and several hypotheses have been proposed in the past decades. Local and regional studies have suggested that area and geometric constraint are two of major factors affecting the elevational pattern of species richness. In this study, using data of seed plants and their distribution ranges and a Digital Elevation Model data set, we explored altitudinal patterns of seed plant richness and quantified the effects of area and the mid-domain effect (MDE) on the richness patterns in a high mountain area, Gaoligong Mountains (ranging from 215 m to 5791 m a.s.l.) located in south-eastern Tibet, China. The results showed that richness and density (richness/log-transformed area) of seed plants at species, genus, and family levels all showed hump-shaped patterns along the altitudinal gradient. The altitudinal changes in richness of species with three different range sizes (< 500 m, 500–1500 m, and > 1500 m), species of different plant life-forms (trees, shrubs, and herbs), and endemic species further confirmed this finding. Analysis of Generalized Linear Model depicted that although the area of each elevational band was always in high correlation with the species richness, the MDE could explain 84.9%, 33.8%, 83.8%, and 84.5% of the total variation in richness for all species and the three species groups with different range sizes, respectively. This suggests that the MDE significantly influences the patterns of species richness and is likely be stronger for broad-ranged species than for narrow-ranged ones in the Gaoligong Mountains.     

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。     

A simulation approach to determine statistical significance of species turnover peaks in a species-rich tropical cloud forest

Use of β-diversity indices in the study of spatial distribution of species diversity is hampered by the difficulty of applying significance tests. To overcome this problem we used a simulation approach in a study of species turnover of ferns, aroids, bromeliads, and melastomes along an elevational gradient from 1700 m to 3400 m in a species-rich tropical cloud forest of Bolivia. Three parameters of species turnover (number of upper/lower elevational species limits per elevational step, Wilson–Shmida similarity index between adjacent steps) were analysed. Significant species turnover limits were detected at 2000 (± 50) m and 3050 m, which roughly coincided with the elevational limits of the main vegetation types recognized in the study area. The taxon specificity of elevational distributions implies that no single plant group can be used as a reliable surrogate for overall plant diversity and that the response to future climate change will be taxon-specific, potentially leading to the formation of plant communities lacking modern analogues. Mean elevational range size of plant species was 490 m (± 369). Elevational range sizes of terrestrial species were shorter than those of epiphytes. We conclude that our simulation approach provides an alternative approach for assessing the statistical significance of levels of species turnover along ecological gradient without the limitations imposed by traditional statistical approaches.     

Elevational Gradient of Vascular Plant Species Richness and Endemism in Crete – The Effect of Post-Isolation Mountain Uplift on a Continental Island System

Understanding diversity patterns along environmental gradients and their underlying mechanisms is a major topic in current biodiversity research. In this study, we investigate for the first time elevational patterns of vascular plant species richness and endemism on a long-isolated continental island (Crete) that has experienced extensive post-isolation mountain uplift. We used all available data on distribution and elevational ranges of the Cretan plants to interpolate their presence between minimum and maximum elevations in 100-m elevational intervals, along the entire elevational gradient of Crete (0–2400 m). We evaluate the influence of elevation, area, mid-domain effect, elevational Rapoport effect and the post-isolation mountain uplift on plant species richness and endemism elevational patterns. Furthermore, we test the influence of the island condition and the post-isolation mountain uplift to the elevational range sizes of the Cretan plants, using the Peloponnese as a continental control area. Total species richness monotonically decreases with increasing elevation, while endemic species richness has a unimodal response to elevation showing a peak at mid-elevation intervals. Area alone explains a significant amount of variation in species richness along the elevational gradient. Mid-domain effect is not the underlying mechanism of the elevational gradient of plant species richness in Crete, and Rapoport''s rule only partly explains the observed patterns. Our results are largely congruent with the post-isolation uplift of the Cretan mountains and their colonization mainly by the available lowland vascular plant species, as high-elevation specialists are almost lacking from the Cretan flora. The increase in the proportion of Cretan endemics with increasing elevation can only be regarded as a result of diversification processes towards Cretan mountains (especially mid-elevation areas), supported by elevation-driven ecological isolation. Cretan plants have experienced elevational range expansion compared to the continental control area, as a result of ecological release triggered by increased species impoverishment with increasing elevation.     

Habitat heterogeneity,temperature, and primary productivity drive elevational gradients in avian species diversity

AimAnticipating and mitigating the impacts of climate change on species diversity in montane ecosystems requires a mechanistic understanding of drivers of current patterns of diversity. We documented the shape of elevational gradients in avian species richness in North America and tested a suite of a priori predictions for each of five mechanistic hypotheses to explain those patterns.LocationUnited StatesMethodsWe used predicted occupancy maps generated from species distribution models for each of 646 breeding birds to document elevational patterns in avian species richness across the six largest U.S. mountain ranges. We used spatially explicit biotic and abiotic data to test five mechanistic hypotheses proposed to explain geographic variation in species richness.ResultsElevational gradients in avian species richness followed a consistent pattern of low elevation plateau‐mid‐elevation peak (as per McCain, 2009). We found support for three of the five hypotheses to explain the underlying cause of this pattern: the habitat heterogeneity, temperature, and primary productivity hypotheses.Main ConclusionsSpecies richness typically decreases with elevation, but the primary cause and precise shape of the relationship remain topics of debate. We used a novel approach to study the richness‐elevation relationship and our results are unique in that they show a consistent relationship between species richness and elevation among 6 mountain ranges, and universal support for three hypotheses proposed to explain the underlying cause of the observed relationship. Taken together, these results suggest that elevational variation in food availability may be the ecological process that best explains elevational gradients in avian species richness in North America. Although much attention has focused on the role of abiotic factors, particularly temperature, in limiting species’ ranges, our results offer compelling evidence that other processes also influence (and may better explain) elevational gradients in species richness.     

Climate and history explain the species richness peak at mid-elevation for Schizothorax fishes (Cypriniformes: Cyprinidae) distributed in the Tibetan Plateau and its adjacent regions

Aim  We studied elevational species richness patterns of Schizothorax fishes and identified the roles of ecological and evolutionary factors in shaping the patterns of elevational diversity.
Location  The Tibetan Plateau and its adjacent regions.
Methods  We assembled distribution and altitude data for all Schizothorax species using the literature. We merged ecological and evolutionary approaches to test the relationships between species richness and ecological factors (climate, area, the mid-domain effect) or evolutionary factors (diversification rates and time of colonization).
Results  We found that species richness of Schizothorax fishes peaked at mid-elevations. Rainfall, area, the mid-domain effect and diversification rate were weak predictors of the richness pattern. Temperature showed a nonlinear relationship with species richness. Temperature and time of colonization were the most important variables in explaining the elevational diversity pattern.
Main conclusion  Our findings indicate that the time-for-speciation effect and niche conservatism play important roles in variation of species richness.     

Spatial diversity patterns of Pristimantis frogs in the Tropical Andes

Although biodiversity gradients have been widely documented, the factors governing broad‐scale patterns in species richness are still a source of intense debate and interest in ecology, evolution, and conservation biology. Here, we tested whether spatial hypotheses (species–area effect, topographic heterogeneity, mid‐domain null model, and latitudinal effect) explain the pattern of diversity observed along the altitudinal gradient of Andean rain frogs of the genus Pristimantis. We compiled a gamma‐diversity database of 378 species of Pristimantis from the tropical Andes, specifically from Colombia to Bolivia, using records collected above 500 m.a.s.l. Analyses were performed at three spatial levels: Tropical Andes as a whole, split in its two main domains (Northern and Central Andes), and split in its 11 main mountain ranges. Species richness, area, and topographic heterogeneity were calculated for each 500‐m‐width elevational band. Spatial hypotheses were tested using linear regression models. We examined the fit of the observed diversity to the mid‐domain hypothesis using randomizations. The species richness of Pristimantis showed a hump‐shaped pattern across most of the altitudinal gradients of the Tropical Andes. There was high variability in the relationship between area and species richness along the Tropical Andes. Correcting for area effects had little impact in the shape of the empirical pattern of biodiversity curves. Mid‐domain models produced similar gradients in species richness relative to empirical gradients, but the fit varied among mountain ranges. The effect of topographic heterogeneity on species richness varied among mountain ranges. There was a significant negative relationship between latitude and species richness. Our findings suggest that spatial processes partially explain the richness patterns of Pristimantis frogs along the Tropical Andes. Explaining the current patterns of biodiversity in this hot spot may require further studies on other possible underlying mechanisms (e.g., historical, biotic, or climatic hypotheses) to elucidate the factors that limit the ranges of species along this elevational gradient.     

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.     

Elevational changes in vascular plants richness,diversity, and distribution pattern in Abune Yosef mountain range,Northern Ethiopia

The aim of this research is to investigate the patterns of vascular plant species richness,diversity,and distribution along an elevation gradient in the Abune Yosef mountain range,Ethiopia.Preferential systematic sampling was employed to collect vegetation and environmental data along the elevation gradient.We found that plant species richness declines monotonically from low to high elevations.Specifically,vascular plant species richness and diversity were lower in the Afroalpine grassland(high elevation)than in the Dry evergreen Afromontane forest and Ericaceous forest(low elevations).In contrast,endemic vascular plant richness was significantly higher in the Afroalpine grassland than in the Dry evergreen Afromontane forest and Ericaceous forest.Elevation showed a significant impact on the richness,diversity,and endemism of vascular plants.According to Sorensen's coefficient,the similarity between Dry evergreen Afromontane forest and Ericaceous forest vegetation types is higher(32%)than the similarity between Ericaceous forest and Afroalpine grassland(18%).Only 5%similarity was recorded between the Dry evergreen Afromontane forest and Afroalpine grassland.Growth forms showed different elevationai richness patterns.Trees and liana increased monotonically up to 3300 m.Shrub and herb richness patterns followed a hump-shaped and inverted hump-shaped pattern along the elevation gradient.The elevation patterns of vascular plant species richness,diversity,and growth form in the present study may be attributed to differences in management intensity,spatial heterogeneity,microclimatic variations,and anthropogenic disturbances.     

Elevational patterns in the vascular flora of a highly diverse region in southern Mexico

We examined general and family-specific patterns of vascular plant richness along a large elevational gradient (0?C3,670?m a.s.l.), assessed the continuity of these patterns and analysed their potential underlying causes in a high diversity region of the Sierra Madre del Sur, Oaxaca, Mexico. We used a vascular plant database constructed previously. The gradient was divided into 18 200-m elevation belts. To examine elevational patterns of richness, we used both observed and estimated (interpolated) species richness, as well as genus and family observed richness, for each belt. A generalised linear model (GLM) was used to assess the effect of altitude on area-corrected species richness (standard area?=?100?km²), and a numerical classification of the elevational belts based on species richness was performed. Overall, richness at the three taxonomic levels decreased with elevation, but some individual families departed from this pattern. A sharp drop in species richness was observed at 1,800?m, and the dendrogram separated two elevational floristic groups at this elevation. The GLM revealed a significant negative effect of elevation on species richness. Despite this overall decreasing pattern for vascular plants along this extensive gradient, an examination of some family-specific patterns revealed the existence of other elevation?Cdiversity relationships, indicating taxon-specific responses to elevation. The most noticeable discontinuity in species richness, at ca. 1,800?m, is likely related to a critical temperature isocline.