太白山北坡小型兽类物种多样性垂直分布格局

物种多样性沿海拔梯度的垂直分布格局一直是生物多样性研究的热点问题,其中最为普遍的分布模式为中峰格局。为了解太白山北坡小型兽类物种组成和物种多样性垂直分布格局,本研究于2020和2021年两年的6至9月采用样线法、铗日法和陷阱法对太白山北坡小型兽类物种进行调查。在海拔780~3767.2 m之间,以200 m为梯度,设置采集样点15个,累计布置4150铗次,陷阱105个,样线8条。共记录小型兽类4目7科12属21种148只,阔叶林中的小型兽类物种多样性普遍高于针叶林,物种多样性在中海拔地区栓皮栎(Quercus variabilis)林、锐齿槲栎(Q.aliena)林最高,高海拔地区秦岭冷杉(Abies fargesii)林最低。小型兽类物种多样性垂直分布格局为左偏倚中峰格局,物种多样性在1500~2300 m海拔段内出现峰值。这种分布格局和林型中小型兽类东洋界与古北界、特有种与非特有种在太白山地区交汇有关,太白山北坡南北纵列的山脉-沟谷地貌为南北物种扩散和迁移提供了有利条件,在沟谷内气候和地理特征相似,形成了规律的林型垂直带谱,这使得小型兽类物种多样性垂直分布也具有相似的特点。     

贡嘎山东坡非飞行小型兽类物种多样性的垂直分布格局

为了解贡嘎山地区物种多样性的垂直分布格局,2010年4—9月利用夹日法对贡嘎山东坡非飞行小型兽类的物种多样性进行了详细调查。调查在海拔1200—4000m之间按400m间隔设置了8个采集样地,累计布夹28800夹次,捕获非飞行小型兽类个体701个,观察记录到松鼠个体25个,共调查记录小兽个体726个,分属于3目6科16属25种。非参数估计的物种丰富度Chao2和Jackknife2指数以及物种累积曲线评估表明本次调查取样充分,能很好地反映该地区非飞行小型兽类物种多样性的垂直分布格局。结果表明:非飞行小型兽类物种多样性的垂直分布格局为单峰模型;物种丰富度和物种多度在中海拔地区最高,在低海拔和高海拔地区较低;相反,物种均匀度在中海拔地区较低,在低海拔和高海拔地区较高;而物种优势度则随着海拔的升高而逐渐增加;Shannon-Wiener、Fisher-α、Margalef三个综合性物种多样性指数均显示物种多样性在中海拔地区最高;与其它多样性指数相比,Simpson指数未能很好地反映出不同海拔段群落物种多样性的垂直分布差异;而与Shannon-Wiener和Simpson指数相比,Fisher-α和Margalef指数对不同物种组成的群落多样性区分较好。同时,基于不同海拔段物种组成的聚类分析结果也表明物种多样性在中海拔地区最高。物种多样性在中海拔地区最高的垂直分布模式提示我们在贡嘎山地区的生物多样性保护和生态管理中应特别重视中海拔地段,因为该地段中居于生态食物链中间位置的小兽物种最丰富,是山地生物多样性保护的关键。此外,规范统一的调查方法将有利于研究数据的整合和减少人为因素带来的误差。     

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.     

The role of spatial scale and the perception of large-scale species-richness patterns

Despite two centuries of exploration, our understanding of factors determining the distribution of life on Earth is in many ways still in its infancy. Much of the disagreement about governing processes of variation in species richness may be the result of differences in our perception of species‐richness patterns. Until recently, most studies of large‐scale species‐richness patterns assumed implicitly that patterns and mechanisms were scale invariant. Illustrated with examples and a quantitative analysis of published data on altitudinal gradients of species richness (n = 204), this review discusses how scale effects (extent and grain size) can influence our perception of patterns and processes. For example, a hump‐shaped altitudinal species‐richness pattern is the most typical (c. 50%), with a monotonic decreasing pattern (c. 25%) also frequently reported, but the relative distribution of patterns changes readily with spatial grain and extent. If we are to attribute relative impact to various factors influencing species richness and distribution and to decide at which point along a spatial and temporal continuum they act, we should not ask only how results vary as a function of scale but also search for consistent patterns in these scale effects. The review concludes with suggestions of potential routes for future analytical exploration of species‐richness patterns.     

Latitudinal patterns of mammalian species richness in the New World: the effects of sampling method and faunal group

Abstract. Although the latitudinal gradient of species richness for mammals in North America is well documented, few investigators have quantified the relationship in South America. We examined the pattern in North and South America, at two spatial scales (2.5° and 5°) for each of two sampling methods (quadrats and latitudinal bands). A scale effect was evident for quadrats but not for bands. Significant linear relationships between species richness and latitude were found for three faunal groups: all mammals, nonvolant species, and bats. Effects of area confound the latitudinal relationship. By statistically removing such effects, we found that the latitudinal gradient is not an artifact of the species-area relationship, and that the latitudinal gradients for North and South America were statistically indistinguishable. Our data suggest that both faunal subgroups, nonvolant species and bats, contributed substantially to the overall mammalian pattern. Further, multiple regression analyses showed that only latitude is a necessary variable to explain bat richness; for nonvolant species, in addition to latitude, area and longitude may be important.     

Analysis of the community structure of abyssal kinetoplastids revealed similar communities at larger spatial scales

Knowledge of the spatial scales of diversity is necessary to evaluate the mechanisms driving biodiversity and biogeography in the vast but poorly understood deep sea. The community structure of kinetoplastids, an important group of microbial eukaryotes belonging to the Euglenozoa, from all abyssal plains of the South Atlantic and two areas of the eastern Mediterranean was studied using partial small subunit ribosomal DNA gene clone libraries. A total of 1364 clones from 10 different regions were retrieved. The analysis revealed statistically not distinguishable communities from both the South-East Atlantic (Angola and Guinea Basin) and the South-West Atlantic (Angola and Brazil Basin) at spatial scales of 1000–3000 km, whereas all other communities were significantly differentiated from one another. It seems likely that multiple processes operate at the same time to shape communities of deep-sea kinetoplastids. Nevertheless, constant and homogenous environmental conditions over large spatial scales at abyssal depths, together with high dispersal capabilities of microbial eukaryotes, maintain best the results of statistically indistinguishable communities at larger spatial scales.     

The mid-domain effect applied to elevational gradients: species richness of small mammals in Costa Rica

Aim The objective of this study was to comprehensively document and examine the alpha and gamma patterns of species richness in non-volant, small mammals (rodents, shrews and mouse opossums) along a tropical elevational gradient. These data were used to determine the support for existing hypotheses of species richness encompassing mid-domain null models, as well as climatic, and community overlap hypotheses. Location Field studies were conducted along a Caribbean slope of the Río Peñas Blancas watershed in the north-eastern region of Costa Rica between 750 and 1850 m at 10 sampling sites. Methods Species richness and abundances of small mammals were surveyed for four seasons including three temporal replicates at each of five elevational sites: late wet season (2000), early wet season (2001), and dry season (2002), and one spatial replicate at five different sites within the same elevations during the late wet season (2001). Species richness at elevations below 700 m was compiled from specimen records from 23 US national and international collections. Predictions of a null model based solely on geometric constraints were examined using a Monte Carlo simulation program, Mid-Domain Null. Results In 16,900 trap nights, 1561 individuals from 16 species were captured. Both alpha and gamma species richness peaked at mid-elevation between 1000 and 1300 m, with richness declining both at higher and lower elevations. Most of the empirical curves of species richness occur within 95% prediction curves of the mid-domain model, although deviations from the null model exist. Regression of the empirical richness on the null model predictions explained nearly half of the variation observed (r² = 0.45, P = 0.002). Main conclusions The geometric constraints of montane topography appear to influence the diversity pattern of small mammals, although climatic conditions including an intermediate rainfall and temperature regime, and distance from the persistent cloud cap also are correlated with the pattern of species richness. The predictions of productivity, and community overlap hypotheses are not supported with the empirical data.     

Niche and metabolic principles explain patterns of diversity and distribution: theory and a case study with soil bacterial communities

The causes of biodiversity patterns are controversial and elusive due to complex environmental variation, covarying changes in communities, and lack of baseline and null theories to differentiate straightforward causes from more complex mechanisms. To address these limitations, we developed general diversity theory integrating metabolic principles with niche-based community assembly. We evaluated this theory by investigating patterns in the diversity and distribution of soil bacteria taxa across four orders of magnitude variation in spatial scale on an Antarctic mountainside in low complexity, highly oligotrophic soils. Our theory predicts that lower temperatures should reduce taxon niche widths along environmental gradients due to decreasing growth rates, and the changing niche widths should lead to contrasting α- and β-diversity patterns. In accord with the predictions, α-diversity, niche widths and occupancies decreased while β-diversity increased with increasing elevation and decreasing temperature. The theory also successfully predicts a hump-shaped relationship between α-diversity and pH and a negative relationship between α-diversity and salinity. Thus, a few simple principles explained systematic microbial diversity variation along multiple gradients. Such general theory can be used to disentangle baseline effects from more complex effects of temperature and other variables on biodiversity patterns in a variety of ecosystems and organisms.