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.     

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.     

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。     

Could temperature and water availability drive elevational species richness patterns? A global case study for bats

Aim A global meta‐analysis was used to elucidate a mechanistic understanding of elevational species richness patterns of bats by examining both regional and local climatic factors, spatial constraints, sampling and interpolation. Based on these results, I propose the first climatic model for elevational gradients in species richness, and test it using preliminary bat data for two previously unexamined mountains. Location Global data set of bat species richness along elevational gradients from Old and New World mountains spanning 12.5° S to 38° N latitude. Methods Bat elevational studies were found through an extensive literature search. Use was made only of studies sampling  70% of the elevational gradient without significant sampling biases or strong anthropogenic disturbance. Undersampling and interpolation were explicitly examined with three levels of error analyses. The influence of spatial constraints was tested with a Monte Carlo simulation program, Mid‐Domain Null. Preliminary bat species richness data sets for two test mountains were compiled from specimen records from 12 US museum collections. Results Equal support was found for decreasing species richness with elevation and mid‐elevation peaks. Patterns were robust to substantial amounts of error, and did not appear to be a consequence of spatial constraints. Bat elevational richness patterns were related to local climatic gradients. Species richness was highest where both temperature and water availability were high, and declined as temperature and water availability decreased. Mid‐elevational peaks occurred on mountains with dry, arid bases, and decreasing species richness occurred on mountains with wet, warm bases. A preliminary analysis of bat richness patterns on elevational gradients in western Peru (dry base) and the Olympic Mountains, WA (wet base), supported the predictions of the climate model. Main conclusions The relationship between species richness and combined temperature and water availability may be due to both direct (thermoregulatory constraints) and indirect (food resources) factors. Abundance was positively correlated with species richness, suggesting that bat species richness may also be related to productivity. The climatic model may be applicable to other taxonomic groups with similar ecological constraints, for instance certain bird, insect and amphibian clades.     

空间尺度对地形异质性-物种多样性关系的影响:粒度和幅度

空间尺度是影响我们理解生态学格局和过程的关键因素.目前已有多种关于物种多样性分布格局形成机制的假说且研究者未达成共识,原因之一是空间尺度对物种多样性分布格局的环境影响因子的解释力和相对重要性有重要影响.地形异质性是物种多样性分布格局的重要影响因素.本文综述了在地形异质性-物种多样性关系的研究中,不同空间粒度和幅度对研究...     

寒温带牧林交错区生境复杂度对啮齿类物种多样性的影响

采用铗日法对嫩江流域牧林交错区5个生境梯度中啮齿动物的多样性水平进行了研究,以探讨栖息地复杂程度对地面啮齿类物种多样性的影响.结果表明,黑线姬鼠、黑线仓鼠和大林姬鼠是嫩江流域牧林交错区中的优势种和常见种,不同物种在不同生境类型中呈明显的不均匀分布,反映了它们对不同生境的选择倾向性.同时,地面草本植物的覆盖度和丰富度对地面活动的小型哺乳动物的物种组成和群落结构具有较大的影响,啮齿动物的捕获率和生物量与草本植物的多样性水平呈现出显著的相关性关系,其物种丰富度随草本植物多样性指数的增加呈递增的趋势.此外,各生境中啮齿动物的物种多样性指数与草本植物多样性的相关关系并不显著,可能是因为灌丛区和林-灌交错区内大量的低矮灌丛与萌生丛改善了生境的隐蔽条件与食物资源,为更多物种的共存创造了良好的微环境,使得两生境中啮齿动物的物种多样性水平尤为突出.研究表明,小型啮齿动物的物种组成与栖息地的复杂程度有关,但地面植被对小型兽类生物量和物种多样性的影响力度并不是等同的,对地面小型兽类物种多样性影响的研究,统计生境复杂度或异质性时应考虑不同植被型/生境类型距地面的高度,不同植被型对小型兽类物种多样性的贡献程度随其距地面高度的增加而降低.