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.     

Epiphytic bryophyte diversity and range distributions along an elevational gradient in Marojejy,Madagascar

Describing spatial variation in species richness and understanding its links to ecological mechanisms are complementary approaches for explaining geographical patterns of richness. The study of elevational gradients holds enormous potential for understanding the factors underlying global diversity. This paper investigates the pattern of species richness and range-size distribution of epiphytic bryophytes along an elevational gradient in Marojejy National Park, northeast Madagascar. The main objectives are to describe bryophyte species composition and endemism in Marojejy National Park, to describe the species richness and distribution patterns of epiphytic bryophytes along an elevational gradient from 250 m to 2050 m and to evaluate the explanatory value of environmental variables for the observed patterns. Bryophyte samples were collected following a nested design with four hierarchical levels: elevational belts, plots, quadrats, and microplots. In total, 254 epiphytic bryophyte species were recorded, comprising 157 liverworts and 97 mosses. Twenty-three of these are endemic to Madagascar. Species richness exhibits a hump-shaped pattern along the elevational gradient, peaking at 1,250 m. Eighty-seven percent of the total recorded species have a range distribution lower than 1,000 m, at which point 36% are restricted to these single elevations. Our results suggest that mean temperature, relative humidity, and vapor pressure deficit play important roles in shaping the richness pattern observed in this study. While the liverwort richness pattern did not correlate to vapor pressure deficit and responded only weakly to relative humidity, the richness pattern shown by mosses correlates well with mean temperature, relative humidity, and vapor pressure deficit.     

Determinants of avian species richness at different spatial scales

ABSTRACT. Studies of factors influencing avian biodiversity yield very different results depending on the spatial scale at which species richness is calculated. Ecological studies at small spatial scales (plot size 0.0025–0.4 km²) emphasize the importance of habitat diversity, whereas biogeographical studies at large spatial scales (quadrat size 400–50,000 km²) emphasize variables related to available energy such as temperature. In order to bridge the gap between those two approaches the bird atlas data set of Lake Constance was used to study factors determining avian species diversity at the intermediate spatial scales of landscapes (quadrat size 4–36 km²). At these spatial scales bird species richness was influenced by habitat diversity and not by variables related to available energy probably because, at the landscape scale, variation in available energy is small. Changing quadrat size between 4 and 36 km², but keeping the geographical extension of the study constant resulted in profound changes in the degree to which the amount of different habitat types was correlated with species richness. This suggests that high species diversity is achieved by different management regimes depending on the spatial scale at which species richness is calculated. However, generally, avian species diversity seems to be determined by spatial heterogeneity at the corresponding spatial scale. Thus, protecting the diversity of landscapes and ecosystems appears to ensure also high levels of species diversity.     

Ecological and evolutionary drivers of the elevational gradient of diversity

Ecological, evolutionary, spatial and neutral theories make distinct predictions and provide distinct explanations for the mechanisms that control the relationship between diversity and the environment. Here, we test predictions of the elevational diversity gradient focusing on Iberian bumblebees, grasshoppers and birds. Processes mediated by local abundance and regional diversity concur in explaining local diversity patterns along elevation. Effects expressed through variation in abundance were similar among taxa and point to the overriding role of a physical factor, temperature. This determines how energy is distributed among individuals and ultimately how the resulting pattern of abundance affects species incidence. Effects expressed through variation in regional species pools depended instead on taxon‐specific evolutionary history, and lead to diverging responses under similar environmental pressures. Local filters and regional variation also explain functional diversity gradients, in line with results from species richness that indicate an (local) ecological and (regional) historical unfolding of diversity–elevation relationships.     

Fern species richness along a central Himalayan elevational gradient, Nepal

Aim The study explores fern species richness patterns along a central Himalayan elevational gradient (100–4800 m a.s.l.) and evaluates factors influencing the spatial increase and decrease of fern richness. Location The Himalayas stretch from west to east by 20°, i.e. 75–95° east, and Nepal is located from 80 to 88° east in this range. Methods We used published data of the distribution of ferns and fern allies to interpolate species elevational ranges. Defining species presence between upper and lower elevation limit is the basis for richness estimates. The richness pattern was regressed against the total number of rainy days, and gradients that are linearly related to elevation, such as length of the growing season, potential evapotranspiration (PET, energy), and a moisture index (MI = PET/mean annual rainfall). The regressions were performed by generalized linear models. Results A unimodal relationship between species richness and elevation was observed, with maximum species richness at 2000 m. Fern richness has a unimodal response along the energy gradients, and a linear response with moisture gradients. Main conclusions The study confirms the importance of moisture on fern distributions as the peak coincides spatially with climatic factors that enhance moisture levels; the maximum number of rainy days and the cloud zone. Energy‐related variables probably control species richness directly at higher elevations but at the lower end the effect is more probably related to moisture.     

长白山不同海拔梯度裸肉足虫群落分布特征

裸肉足虫作为联结微生物和大中型土壤动物的重要环节, 在土壤生态系统物质循环和能量流动过程中起着重要作用。为探明裸肉足虫群落沿海拔梯度的分布特征及其主要驱动因子, 作者在长白山北坡选择不同海拔梯度(700 m、1,000 m、1,300 m、1,600 m、1,900 m和2,200 m), 采用最大可能数法对裸肉足虫进行了培养计数, 并采用平板培养、标记、分离再培养的方法进行了分类鉴定, 分析比较了不同海拔梯度裸肉足虫的群落组成和结构特征。结果表明: 长白山北坡裸肉足虫物种丰富, 不同海拔梯度裸肉足虫丰富度指数存在显著差异, 且与土壤酸碱度呈极显著正相关关系。其中林分较为单一的岳桦(Betula ermanii)林带(1,900 m)裸肉足虫丰富度最低, 位于植被交错带的针阔混交林带(1,000 m)裸肉足虫丰富度最大, Shannon-Wiener多样性指数和Pielou均匀度指数在不同海拔梯度间不存在显著性差异, 但变化趋势与丰富度一致。聚类分析结果显示, 1,300 m、1,600 m和1,900 m海拔带以及700 m和2,200 m海拔带裸肉足虫群落组成较为相似。典范对应分析(canonical correspondence analysis, CCA)显示, 裸肉足虫群落组成和结构主要受土壤酸碱度、铵态氮以及碳氮比的影响, 而海拔和土壤含水量对其没有显著影响。综上, 裸肉足虫群落多样性随海拔梯度的增加并未呈现递减或单峰的变化趋势, 土壤的基本理化性质是驱动裸肉足虫群落分布的主要因素; 此外, 地上植被也可能通过凋落物和根系分泌物间接影响裸肉足虫的群落组成和多样性。     

Functional traits reveal the expansion and packing of ecological niche space underlying an elevational diversity gradient in passerine birds

Variation in species richness across environmental gradients may be associated with an expanded volume or increased packing of ecological niche space. However, the relative importance of these alternative scenarios remains unknown, largely because standardized information on functional traits and their ecological relevance is lacking for major diversity gradients. Here, we combine data on morphological and ecological traits for 523 species of passerine birds distributed across an Andes-to-Amazon elevation gradient. We show that morphological traits capture substantial variation in species dietary (75%) and foraging niches (60%) when multiple independent trait dimensions are considered. Having established these relationships, we show that the 14-fold increase in species richness towards the lowlands is associated with both an increased volume and density of functional trait space. However, we find that increases in volume contribute little to changes in richness, with most (78%) lowland species occurring within the range of trait space occupied at high elevations. Taken together, our results suggest that high species richness is mainly associated with a denser occupation of functional trait space, implying an increased specialization or overlap of ecological niches, and supporting the view that niche packing is the dominant trend underlying gradients of increasing biodiversity towards the lowland tropics.     

Functional diversity of avian communities increases with canopy height: From individual behavior to continental‐scale patterns

Vegetation complexity is an important predictor of animal species diversity. Specifically, taller vegetation should provide more potential ecological niches and thus harbor communities with higher species richness and functional diversity (FD). Resource use behavior is an especially important functional trait because it links species to their resource base with direct relevance to niche partitioning. However, it is unclear how exactly the diversity of resource use behavior changes with vegetation complexity. To address this question, we studied avian FD in relation to vegetation complexity along a continental‐scale vegetation gradient. We quantified foraging behavior of passerine birds in terms of foraging method and substrate use at 21 sites (63 transects) spanning 3,000 km of woodlands and forests in Australia. We also quantified vegetation structure on 630 sampling points at the same sites. Additionally, we measured morphological traits for all 111 observed species in museum collections. We calculated individual‐based, abundance‐weighted FD in morphology and foraging behavior and related it to species richness and vegetation complexity (indexed by canopy height) using structural equation modeling, rarefaction analyses, and distance‐based metrics. FD of morphology and foraging methods was best predicted by species richness. However, FD of substrate use was best predicted by canopy height (ranging 10–30 m), but only when substrates were categorized with fine resolution (17 categories), not when categorized coarsely (8 categories). These results suggest that, first, FD might increase with vegetation complexity independently of species richness, but whether it does so depends on the studied functional trait. Second, patterns found might be shaped by how finely we categorize functional traits. More complex vegetation provided larger "ecological space" with more resources, allowing the coexistence of more species with disproportionately more diverse foraging substrate use. We suggest that the latter pattern was driven by nonrandom accumulation of functionally distinct species with increasing canopy height.     

Patterns of ant species richness along elevational gradients in an arid ecosystem

Aim In this study, we examine patterns of local and regional ant species richness along three elevational gradients in an arid ecosystem. In addition, we test the hypothesis that changes in ant species richness with elevation are related to elevation‐dependent changes in climate and available area. Location Spring Mountains, Nevada, U.S.A. Methods We used pitfall traps placed at each 100‐m elevational band in three canyons in the Spring Mountains. We compiled climate data from 68 nearby weather stations. We used multiple regression analysis to examine the effects of annual precipitation, average July precipitation, and maximum and minimum July temperature on ant species richness at each elevational band. Results We found that patterns of local ant species richness differed among the three gradients we sampled. Ant species richness increased linearly with elevation along two transects and peaked at mid‐elevation along a third transect. This suggests that patterns of species richness based on data from single transects may not generalize to larger spatial scales. Cluster analysis of community similarity revealed a high‐elevation species assemblage largely distinct from that of lower elevations. Major changes in the identity of ant species present along elevational gradients tended to coincide with changes in the dominant vegetation. Regional species richness, defined here as the total number of unique species within an elevational band in all three gradients combined, tended to increase with increasing elevation. Available area decreased with increasing elevation. Area was therefore correlated negatively with ant species richness and did not explain elevational patterns of ant species richness in the Spring Mountains. Mean July maximum and minimum temperature, July precipitation and annual precipitation combined to explain 80% of the variation in ant species richness. Main conclusions Our results suggest that in arid ecosystems, species richness for some taxa may be highest at high elevations, where lower temperatures and higher precipitation may support higher levels of primary production and cause lower levels of physiological stress.     

神农架自然保护区非飞行哺乳动物的物种丰富度:沿海拔梯度的分布格局

于1999～2001年调查了神农架自然保护区6个地点不同栖息地的非飞行哺乳动物的物种丰富度。栖息地分为8类：原始林、择伐林（采伐枯立木）、次生林、灌木林、草地、常年性河流水溪、农田和人居住区。小型非飞行哺乳动物调查用捕鼠夹;大型非飞行哺乳动物调查主要根据皮张收购资料以及样线法和痕迹法;用10 m×10 m的样方调查林地树种丰富度。调查发现,神农架自然保护区有非飞行哺乳动物59种［不包括引进种梅花鹿（Cervus nippon）］。在同一海拔高度,原始林通常比择伐林和次生林的物种丰富度高,说明采伐严重降低了物种丰富度。对比同一栖息地不同海拔高度的物种丰富度,我们发现,在中海拔地段（800～1700 m）物种丰富度最高：如在原始林和次生林,海拔1700 m的东溪物种丰富度最高;在择伐林,海拔800 m的九冲物种丰富度最高。聚类分析显示,6个地点的哺乳动物物种组成可以分为两组：高海拔组（2100 m以上）和中低海拔组（1700 m以下）。各地点的哺乳动物物种组成与植被的垂直分布是一致的。各地点的物种丰富度与单位面积（100 m²）树种平均丰富度、栖息地类型数和海拔高度相关。3个环境变量间也是相关的：海拔高度对单位面积树种平均丰富度和栖息地类型数有重要影响。根据研究结果提出两点保护建议：第一,保护区的移民迁出和退耕还林工程应首先在物种丰富度最高的九冲进行,而后是东溪和下谷;第二,为了增加个体流和基因流,保护区东西两片相间的非保护区地带应划入保护区,建立栖息地廊道。     

中亚热带森林土壤微生物群落多样性随海拔梯度的变化

运用Biolog EcoPlate技术, 对武夷山不同海拔植被带(常绿阔叶林(EBF)、针叶林(CF)、亚高山矮林(DF)、高山草甸(AM))土壤微生物群落多样性差异进行了研究。结果表明: 不同海拔植被带土壤微生物群落功能多样性差异显著。土壤平均颜色变化率(AWCD)随培养时间延长而逐渐增加, 同一深度土层的AWCD值随海拔升高而逐渐降低, 大小顺序依次为EFB > CF > DF > AM。同一海拔植被带, 不同深度土层的AWCD值总体趋势依次为0-10 cm > 10-25 cm > 25-40 cm。土壤微生物群落Simpson指数、Shannon-Wiener指数、丰富度指数和McIntosh指数的总体趋势为EBF最高, CF和DF次之, AM最低。不同海拔植被带土壤微生物对不同碳源利用强度存在较大差异, 其中EBF利用率最高, AM利用率最低, 碳水化合物和羧酸类碳源是各海拔植被带土壤微生物的主要碳源。主成分分析结果表明, 从31个因素中提取的与碳源利用相关的主成分1、主成分2分别能解释变量方差的75.27%和16.14%, 在主成分分离中起主要贡献作用的是胺类和氨基酸类碳源。土壤微生物群落多样性随着海拔上升、土层加深而逐渐下降的原因, 可能是生物量、林分凋落物、土壤养分、微小动物、植物根系等多种因素共同作用的结果。     

Diversity of geometrid moths (Lepidoptera: Geometridae) along an Afrotropical elevational rainforest transect

Geometrid moths were investigated at 26 sites on 9 elevational levels along an elevational transect at Mt. Kilimanjaro (Tanzania), stretching from the fine‐grained mosaic of small agroforest plots with combined cultivation of trees, shrubs and crops at 1650 m through mountain rainforest to heathland at 3300 m. We sampled moths manually at light between 19 : 00 and 22 : 00 in the rainy seasons of March to May and October to January in the years 2000, 2001 and 2002. Along the transect, the composition of moth communities changed from a domination by Sterrhinae and Ennominae to a dominance of Larentiinae with increasing elevation. Overall, alpha diversity was very low compared to other tropical mountain regions. Fisher's alpha showed a maximum of 30 in the agroforest mosaic at 1650 m and decreased to values around 12 in the mountain rainforest. Communities of geometrid moths within the forest belt were significantly dissimilar from communities outside the forest. The diversity patterns on Mt. Kilimanjaro can be related to the young age, island‐like position and history of the mountain. These factors have led to the formation of a homogeneous upper mountain rainforest habitat which in turn houses homogeneous moth communities with a low diversity compared to habitats at lower elevations. Here, a heterogeneous habitat mosaic allowing the intrusion of savannah species into this former forest habitat may account for an increased diversity. In the heath zone above the forest, climatic conditions are very harsh, permitting only few specialists to thrive in this ericaceous woodland. Edge effects were discernible at the forest–heathland boundary where some moth species from heathland invaded the closed forest. At the boundary between agroforest and a forest mosaic of exotic Acacia and Eucalyptus forest plantations and natural mountain forest, diversity values remained low as the dominant species Chiasmia fuscataria accounted for far higher proportions than other dominant species in any of the other habitats.