Mammalian species richness and morphological complexity along an elevational gradient in the arid south-west

Aim We examined the relationship between species richness and morphological complexity of terrestrial mammal communities along an elevational gradient. Location The gradient is in the Sonoran Desert in Southern California and extends from a sand dune habitat near sea level to coniferous forest ending at >2600 m. Methods Morphological diversity, characterized by both size and shape of coexisting mammal species, was estimated within and between sites from projections of variables on principal components axes. Similarities among species were calculated as Euclidean distances. To tease apart size and shape, we constructed two principal component analyses: one based on log-transformed original measurements, the other on log-transformed proportional shape variables. To test whether species number accounted for the morphological diversity at each site we designed two null models. The models generated were random communities generated from the forty-two-species pool. Indices of morphological diversity for real communities were compared with the results of 500 simulations of each null model. Results Species richness varied along the gradient, peaking in the mid-elevation agave-ocotillo habitat. Morphological diversity of shapes and sizes correlated strongly with species richness. Locomotor, tooth, and skull traits were all important in distinguishing among species. Main conclusions Two important patterns emerged: (1) diversity of both sizes and of shapes of species within communities correlated positively with species number, and both sets of variables behaved similarly across this gradient; (2) the most species rich sites were not composed of specialists on these best places, but rather, a community of species derived from overlapping faunal groups.     

Patterns of diversity and range size of selected plant groups along an elevational transect in the Bolivian Andes

Patterns of point, -, and -diversity, and of an index of range size were studied for Acanthaceae, Araceae, Bromeliaceae, Melastomataceae, Palmae, and Pteridophyta in 204 vegetation plots of 400 m² along an elevational gradient in humid montane forest at 220–3950 m in central Bolivia. Zonal forest point-diversity (mean species number per plot) and -diversity (extrapolated total species number) showed either hump-shaped curves or constant values from lowlands to mid-elevations, followed by a steep decline. These patterns correspond to the hypothesis of maximum diversity at intermediate levels of productivity, while for pteridophytes and epiphytic Bromeliaceae they also fitt a null-model of random distribution within bounded geographical ranges. The ratio of point to -diversity was surprisingly constant across study groups and elevation with values of 0.2–0.4. Range size index (mean inverse range size of all species recorded at a given elevation) either increased with elevation, showed hump-shaped patterns, or remained roughly constant. Non-zonal habitats (ravines, ridge-tops, rock faces, roadsides, pastures) contributed significantly to overall species number for terrestrial herbs and shrubs of Bromeliaceae, Melastomataceae, and Pteridophyta, but not for Acanthaceae, Araceae, and epiphytic taxa. With few exceptions, endemism was most pronounced in zonal forests. These results imply that conservation measures should focus on zonal forests in a few large reserves at low and mid-elevations and in many smaller reserves at higher elevations.     

Phylogeny,niche conservatism and the latitudinal diversity gradient in mammals

Biologists have long searched for mechanisms responsible for the increase in species richness with decreasing latitude. The strong correlation between species richness and climate is frequently interpreted as reflecting a causal link via processes linked to energy or evolutionary rates. Here, we investigate how the aggregation of clades, as dictated by phylogeny, can give rise to significant climate–richness gradients without gradients in diversification or environmental carrying capacity. The relationship between climate and species richness varies considerably between clades, regions and time periods in a global-scale phylogenetically informed analysis of all terrestrial mammal species. Many young clades show negative richness–temperature slopes (more species at cooler temperatures), with the ages of these clades coinciding with the expansion of temperate climate zones in the late Eocene. In carnivores, we find steeply positive richness–temperature slopes in clades with restricted distributions and tropical origins (e.g. cat clade), whereas widespread, temperate clades exhibit shallow, negative slopes (e.g. dog–bear clade). We show that the slope of the global climate–richness gradient in mammals is driven by aggregating Chiroptera (bats) with their Eutherian sister group. Our findings indicate that the evolutionary history should be accounted for as part of any search for causal links between environment and species richness.     

Exploring the generality of associations between plant functional traits: evidence within ecological groups along an altitudinal gradient in Hyrcanian forest

We hypothesized that associations among plant functional traits may differ within different ecological assemblages and plant communities. Association among plant traits including plant maximum height, seed weight, fruit type, pollination mode, mean leaf area, and leaf type were explored within life forms, plant strategy groups along with lowland and montane forest vegetation. In total, 83 sampling plots of 400 m² were placed along a 2400 m altitudinal gradient in Hyrcanian forest. Importance‐values of species within vegetation types were used for weighting data and trait associations were explored using categorical principal component analysis. A G‐test and Fisher's exact test of independence were used to retest significance of the correlations. Different paired trait associations (association lines) including height–leaf, height–seed, height–pollination, leaf–seed, seed–fruit and fruit–pollination were observed and their ecological or physiological basis was discussed. Life forms, strategy types and vegetation types differed based on association lines. Some of the well‐known trade‐offs appear by increasing scale from ecological groups to vegetation types in Hyrcanian forest. The observed patterns of trait associations in Hyrcanian forest and several other ecosystems of the world call the generality of previously accepted trait correlations into question.     

Phylogenetic diversity,structure and diversification patterns of endemic plants along the elevational gradient in the Eastern Himalaya

ABSTRACT

Background: Several studies have documented the variation in species diversity patterns along elevational gradients in the Himalaya, but few have reported the evolutionary and biogeographic processes behind these patterns.

Aims: To understand whether evolutionary history and phylogeny have any role in structuring plant species communities along an elevational gradient in the Sikkim Himalaya.

Methods: We used data on endemic plant species occurrence from primary and secondary sources to construct family-level phylogenetic supertrees for different growth forms with the help of Phylomatic tool of Phylocom. These phylogenetic supertrees were used as a base for testing phylogenetic diversity (PD), niche conservatism, diversification time patterns and phylogenetic structure of various plant growth forms along an elevational gradient.

Results: PD was the highest at mid-elevations for all growth forms and PD had a significant positive correlation with endemic species richness. Species at mid-elevations were dominated by the ancestral/primitive taxa. There was phylogenetic clustering at higher elevations and phylogenetic overdispersion at lower and mid-elevations for the majority of the growth forms.

Conclusions: Time-for-speciation effect and niche conservatism along elevation (retention of niche-related ancestral elevational distribution over evolutionary time scale by species) together determine plant species diversity patterns in the Himalaya.     

Functional diversity and composition of bryophyte water-related traits in Azorean native vegetation

Background: Functional trait-based approaches link species diversity patterns to ecosystem functioning. In the context of global change, understanding these links is vital for developing holistic biodiversity management strategies. Bryophytes, important ecosystem components owing to their biogeochemical functions, have not been the focus of many functional studies.

Aims: This is the first assessment of bryophyte functional diversity in the Azores archipelago, aiming to uncover multivariate trait richness and composition patterns along the elevational gradient on Terceira Island.

Methods: Based on five water acquisition and retention traits of leafy liverworts and mosses, we calculated functional diversity metrics within and among six bryophyte communities sampled along a 1021-m elevational transect.

Results: Trait composition differed significantly between coastal and mountain communities. Mosses presented inrolled leaves and ornamented leaf cells at low elevation but not at high elevation. These patterns were associated with an uphill shift from drier and warmer conditions to a moister and cooler environment.

Conclusions: Future climatic changes might affect bryophyte functional diversity patterns in Terceira Island, particularly for mosses. These results can be directly compared with those obtained for other archipelagos where the same protocol has been applied, allowing a joint assessment of insular vegetation functional diversity patterns.     

The relationship between geographic area and the latitudinal gradient in species richness in New World birds

One hypothesis for the latitudinal gradient in species richness observed in most animal taxa is that the richness of a region is determined by its geographic area. However, the relationship between geographic area and species richness across regions is generally weak. It has been suggested that this is because species from the tropics spill out of this region of high richness, artificially inflating the richness of other regions. This generates the interesting prediction that the area and richness of extra-tropical regions should be more strongly correlated if tropical species are excluded. We test this prediction using the avifauna of the New World. We find that there is indeed a relationship between the land area and species richness of a region once tropical species are excluded. This relationship is independent of the latitude and productivity of regions. Both latitude and productivity can explain variance in richness unexplained by land area. There is no relationship between land area and species richness if tropical species are not excluded from the analysis, suggesting that tropical species do indeed mask the relationship between richness and area. We conclude that our results generally support the geographic area hypothesis, although tests of its other predictions and on other land masses are required.     

Species diversity and ecological range in relation to ploidy level in the flora of the Pyrenees

Polyploidy is a major process in plant evolution. Surprisingly, no study has examined its role in species diversification and ecological distribution in relation to other life history traits. In this study, we examine to what extent polyploidy and the other traditionally examined biological traits (pollination mode, dispersal mode and growth form) account for ecological and taxonomic diversity in the flora of the Pyrenees. Fifty genera (in 22 angiosperm families) were classified according to ploidy level, growth form, pollination mode and dispersal mode, and 451 species and/or subspecies in these 50 genera were classified according to ploidy level and growth form. We examined the contribution of ploidy level, pollination and dispersal modes and growth form to (i) the ecological range of species and genera, i.e., the number of natural habitats (defined by a combination of ecological characteristics) where they occur, and (ii) the taxonomic diversity of the 50 genera. Ploidy level and dispersal mode had significant effects on the taxonomic diversity of the 50 genera. Taxonomic diversity, but not polyploidy per se, was significantly correlated with ecological range of genera. For individual species, diploids had a larger ecological range than polyploids, and herbaceous growth forms had wider ecological distributions than other growth forms. Our results indicate that polyploidisation may be a source of ecological diversification of genera, not by increasing the ecological range of particular polyploid species compared to diploids, but rather by creating taxonomic diversity that leads in some genera to a diversification of the habitats occupied by different ploidy levels. This observation is consistent with previous observations of ecological divergence of chromosomal races in some species in the Alps and in the Pyrenees. As found in other studies, species diversification in the studied flora appears to be greatly influenced by the occurrence of multiple dispersal modes, while ecological range of species or subspecies is significantly increased by the presence of herbaceous species.     

Relative effects of time for speciation and tropical niche conservatism on the latitudinal diversity gradient of phyllostomid bats

Determinants of contemporary patterns of diversity, particularly those spanning extensive latitudinal gradients, are some of the most intensely debated issues in ecology. Recently, focus has shifted from a contemporary environmental perspective to a historical one in an attempt to better understand the construction of latitudinal gradients. Although the vast majority of research on historical mechanisms has focused on tropical niche conservatism (TNC), other historical scenarios could produce similar latitudinal gradients. Herein, I formalize predictions to distinguish between two such historical processes--namely time for speciation (TFS) and TNC--and test relative support based on diversity gradients of New World bats. TFS and TNC are distinctly spatial and environmental mechanisms, respectively. Nonetheless, because of the way that environmental characteristics vary spatially, these two mechanisms are hard to distinguish. Evidence provided herein suggests that TNC has had a more important effect than TFS in determining diversity gradients of New World bats. Indeed, relative effects of different historical mechanisms, as well as relative effects of historical and contemporary environmental determinants, are probably context-dependent. Future research should move away from attempting to identify the mechanism with primacy and instead attempt to understand the particular contexts in which different mechanisms have greater influence on diversity gradients.     

Biogeography of the Amazon molly: ecological niche and range limits of an asexual hybrid species

Aim To understand the relative contributions of environmental factors, dispersal limitations and the presence of sperm donors in determining the distribution of the Amazon molly (Poecilia formosa), a sperm‐dependent unisexual fish species of hybrid origin. To explore niche similarities and/or differences between the hybrid and parental species. To evaluate whether large‐scale abiotic factors can explain a successful introduction of both P. formosa and Poecilia latipinna. Location South‐east United States, Mexico and Central America. Methods We used abiotic variables in ecological niche modelling (ENM) to identify regions with suitable conditions for the presence of the Amazon molly and its two parental species (P. latipinna and Poecilia mexicana). We also used a recently developed metric to calculate the degree of niche overlap between the hybrid and its parental species. Results ENM produced highly significant models [all area under the curve (AUC) > 0.99 for the three species]. Annual mean temperature and minimum temperature of the coldest month were the variables that best explained the distribution of the Amazon molly. With the exception of south Florida, few areas beyond the known distribution of the species were predicted to have suitable environmental conditions. The hybrid species niche overlaps partially with the parental species. However, given the available data, it is neither more similar nor more different than expected by chance. Main conclusions Two different processes are acting to limit the distribution of P. formosa. At the northern limit, although a sperm donor species is present further north, suitable environmental conditions are absent from nearby locations. At the southern limit, a sperm donor species is present and areas with good environmental conditions are present at nearby locations, suggesting that dispersal ability is the limiting factor. We found that the hybrid species overlaps in a similar way with both parental species while still having its own niche identity. This result may be explained by the fact that hybrid species inherit characteristics of two ecologically divergent species, which can result in intermediate or even transgressive phenotypes. These results support recent work on the role of hybridization in diversification.     

Testing the intermediate disturbance hypothesis on species diversity in herbaceous plant communities along a human trampling gradient using a 4-year experiment in an old-field

The intermediate disturbance hypothesis predicts unimodal relationships between species diversity and disturbance frequency/intensity. To test this hypothesis, species diversity in herbaceous plant communities along a human trampling gradient was investigated by conducting a 4-year experiment in an old-field. In general, species richness (S), the Shannon–Weiner index (H) from plant cover data and species evenness (J) showed negative linear relationships with trampling frequency, in contrast to the prediction of the intermediate disturbance hypothesis. However, the significant relationships between trampling frequency and species diversity were not observed in the fourth year without J, which showed a unimodal relationship. In all experimental years, the number of new species that colonized the plots after 1year was small under frequent trampling, and the number of species lost from the plots was large under infrequent trampling. The relative number and the relative cover of perennial species increased as trampling frequency increased in the first and second years, but this pattern was not observed in the following years because the dominance of perennials further increased at decreasing frequencies of trampling. The similarity in the species composition and the yearly changes in species dominance indicated that trampling at higher frequencies eliminated more trampling-intolerant species only in the early years of the experiment. These results suggest that trampling mediated early changes in species diversity patterns, but competitive interactions were more important in the later experimental years. The time lag in the effects of trampling and competition appears to be attributable to the infrequent occurrence of unimodal patterns of species diversity.     

麦套春棉主要害虫和天敌的生态位研究

调查了麦套着棉不同时期内,棉株上、中、下部棉蚜AphisgossypiiGover、棉叶螨TetranychustruncatusEhara、棉铃虫Helicoverpaarmigera（Hubner）和其主要天敌的数量。求得各期害虫与害虫、害虫与天敌、天敌与天敌之间的生态位宽度和重叠指数,并分析了它们彼此在空间上的竞争关系。     

Fauna characteristics and ecological distribution of Carnivora and Artiodactyla in Niubeiliang National Nature Reserve, China

Niubeiliang National Nature Reserve (NNR, 108°45′–109°04′E, 33°47′–33°56′N) is located on the eastern range of the Qinling Mountains in Shaanxi Province, China and spans the southern and northern slopes of Mt. Qinling. A transect survey and investigation were carried out in NNR to determine the fauna characteristics and ecological distribution of carnivora and artiodactyla from May 2003 to August 2004. The NNR has 18 mammals (carnivore and artiodactyl), two of which belong to the first class and seven to the second class of state key protected wildlife in China. The results of this study indicated that ungulates were abundant in the NNR, as all ungulates that were distributed within Mt. Qinling could be found within the reserve. However, only 45.5% of the carnivores distributed within Mt. Qinling were detected within the NNR. Among the mammals, there were 12 oriental species (66.7%), 1 palearctic specie (5.5%) and 5 widely-distributed species (27.8%). The NNR is a crossing area of palearctic species and oriental species on the zoogeographical regions, and it is a transitional area from the oriental realm to the palearctic realm. The results of the analysis on the ecological distribution of carnivore and artiodactyl in the area showed that their elevation ranges had large differences. The species whose elevation ranges above 1 300 m, about 1 000 m, and in 450–700 m occupied one third respectively. The results also indicated that species richness for the memals in the NNR peaked at a middle elevation (rising at first, then descending with the increase in elevation). Not only on the southern slope, but also on the northern slope of Mt. Qinling, the number of species distributed in the area at 1 800–2 200 m a.s.l. was the largest (more than 80%), while the number of species distributed in the area above 2 600 m a.s.l. was the smallest (about 50%). Elevation gradients of species richness for the mammals in the NNR also embodied the mammal distributions among the vegetation types. The number of species distributed in the mixed coniferous and broadleaf deciduous forest at middle elevations was the largest, while the number of species distributed in the broadleaf deciduous forest at middle and low elevations, subalpine coniferous forest, subalpine shrubbery and meadow was relatively smaller. Translated from Acta Ecologica Sinica, 2005, 25(9): 2249–2255 [译自: 生态学报]     

Fauna characteristics and ecological distribution of Carnivora and Artiodactyla in Niubeiliang National Nature Reserve,China

Niubeiliang National Nature Reserve (NNR,108°45'-109°04'E,33°47'-33°56'N)is located on the eastern range of the Qinling Mountains in Shannxi Province,China and spans the southern and northern slopes of Mt.Qiuling.A transect survey and investigation were carried out in NNR to determine the fauna characteristics and ecological distribution of carnivora and artiodactyla from May 2003 to August 2004.The NNR has 18 mammals (carnivore and artiodactyl),two of which belong to the first class and seven to the second class of state key protected wildlife in China.The results of this study indicated that ungulates were abundant in the NNR,as all ungulates that were distributed within bit.Qiuling could be found within the reserve.However,only45.5%of the carnivores distributed within Mt.Qinling were detected within the NNR.Among the mammals,there were 12 oriental species (66.7%),1 palearctic specie (5.5%)and 5 widely-distributed species (27.8%).The NNR is a crossing area of palearctic species and oriental species on the zoogeographical regions,and it is a transitional area from the oriental realm to the palearctic realm.The results of the analysis on the ecological distribution of carnivore and artiodactyl in the area showed that their elevation ranges had large differences.The species whose elevation ranges above 1300 m,about 1000 m,and in 450-700 m occupied one third respectively.The results also indicated that species richness for the mammals in the NNR peaked at a middle elevation (rising at first,then descending with the increase in elevation).Not only on the southern slope,but also on the northern slope of Mt.Qinling,the number of species distributed in the area at 1800-2200 m a.s.l.was the largest (more than 80%),while the number of species distributed in the area above 2 600 m a.s.l.was the smallest (about 50%).Elevation gradients of species richness for the mammals in the NNR also embodied the mammal distributions among the vegetation types.The number of species distributed in the mixed coniferous and broadleaf deciduous forest at middle elevations was the largest,while the number of species distributed in the broadleaf deciduous forest at middle and low elevations,subalpine coniferous forest,subalpine shrubbery and meadow was relatively smaller.     

退化次生林恢复过程中群落结构和生态位动态

在海南白沙县南开乡按人为干扰程度的不同依次选取次生演替中植被恢复初期、早期、近中期和后期4个典型群落,分别对群落结构、树种组成、重要值和生态位宽度等指标进行研究。结果表明:中前期次生演替过程中优势种作用明显,具有最大的生态位宽度;随着次生演替的进行,种群生态位宽度趋于均衡,群落表现出物种丰富度和多样性增加、林分结构复杂化、树种的优势作用弱化等正向演替的趋势;此外,该地区由于经营史的特殊性,中前期次生群落保留了很多原始林的痕迹,出现了一些本应在原始林内出现的生态稳定种,这些物种在中前期次生群落中数量少,生态位宽度小,却表现出强大的生活力;在演替中前期次生林的经营中,最大程度地发挥优势树种的作用、增加林内生态稳定种的数量是该地区次生林恢复经营的重要技术方向。     

三峡水库消落带植物群落组成及物种多样性

研究消落带植物群落多样性的梯度变化和空间分布特征,可为认识和保护消落带生物多样性提供依据。通过对三峡库区澎溪河开县段的植被样方调查,研究消落带植物群落物种多样性的梯度变化和空间分布特征。结果表明:(1)各群落优势种和伴生种的种类和优势度等组成特征变化明显;(2)群落物种丰富度随高程增加而呈先升后降的格局;(3)α多样性与β多样性起伏较大,其中Shannon多样性和Simpson优势度的变化格局相反,其沿高程的曲线变化分别呈M和W型,Pielou均匀度的变化格局基本与丰富度一致,呈先升后降的趋势;相异性指数和Cody指数呈先降后升的格局,最小值均出现在中间高程,最大值出现在较高高程。分析认为,消落带α多样性的变化来自于高程差异造成的淹水时间的差异而导致的生境差异;β多样性变化原因较为复杂,需进一步研究。     

Variation of biomass and morphology of the cushion plant Androsace tapete along an elevational gradient in the Tibetan Plateau

Alpine ecosystems are among those biomes that are most vulnerable to climate change. Cushion plants are an important life form of alpine ecosystems and will likely play a critical role for the resilience of these habitats to climate change. We studied cushion size distribution and different measures of the compactness of cushions (biomass and rosette density, leaf area index) of the cushion plant, Androsace tapete along an elevational gradient from 4500 to 5200 m a.s.l. in the Nyainqentanglha Mountains of the central Tibetan Plateau. Cushion size distribution, total cover, and compactness of cushions varied substantially along the elevational gradient. At the driest site at low elevation we found the lowest total cushion cover, a particularly high proportion of very small cushions, and the most compact cushions (highest rosette and biomass densities, and leaf area index (LAI) per cushion). Our results indicate that in the semi‐arid Tibetan Plateau water availability is the more important climate factor than temperature affecting cushion plant traits and morphology.