Evaluating models to assess the distribution of Buxus balearica in southern Spain

Question: Which is the best model to predict the habitat distribution of Buxus balearica Lam. in southern Spain? Location: Málaga and Granada, Spain, across an area of 38 180 km². Methods: Prediction models based on 17 environmental variables were tested. Six methods were compared: multivariate adaptive regression spline (MARS), maximum entropy approach to modelling species' distributions (Maxent), two generic algorithms based on environmental metrics dissimilarity (BIOCLIM and DOMAIN), Genetic Algorithm for Rule‐set Prediction (GARP), and supervised learning methods based on generalized linear classifiers (support vector machines, SVMs). To test the predictive power of the models we used the Kappa index. Results: Maxent most accurately predicted the habitat distribution of B. balearica, followed by MARS models. The other models tested yielded lower accuracy values. A comparison of the predictive power of the models revealed that climate variables made the highest contributions among the environmental variables studied. The variables that made the lowest contributions were the insolation models. To examine the sensitivity of the models to a reduction in the number of variables, a test showed that accuracy of over 0.90 was maintained by applying just three climatic variables (spring rainfall, mean temperature of the warmest month, and mean temperature of the coldest month). Maps derived from the algorithms of all models tested coincided well with the known distribution of the species. Conclusions: Model habitat prediction is a preliminary step towards highlighting areas of high habitat suitability of B. balearica. These data support the results of previous research, which show that MaxEnt is the best technique for modelling species distributions with small sample sizes.     

Distribution of fingerling brook trout, Salvelinus fontinalis (Mitchill), in dissolved oxygen concentration gradients

A self-recording linear gradient tank and procedures are described in which individual brook trout fingerlings unstressed by recent transfer, unaccustomed surroundings or the presence of an observer could move freely in 16 oxygen concentration gradients within the limits of 1 and 8.9 mg O₂1⁻¹. They avoided oxygen concentrations below 4 mg 1⁻¹ most of the time and preferred 5 mg 1⁻¹ or higher more than half the time, which supports the field-derived belief that fish avoid oxygen concentrations below 5 mg l⁻¹ in the natural environment if they can.     

中国地卷属地衣海拔分布分析

海拔是地衣多样性的重要影响因素。了解地衣的海拔分布格局是地衣多样性保护的基础。研究表明中国地卷属地衣的物种丰富度和个体丰富度沿海拔梯度呈单峰曲线,它们倾向于分布在受全球变暖影响较高的高海拔地区[（2,022±995）m],且具有较窄的海拔分布幅（约68%的物种分布于海拔为1,694－2,954m的地带）,因而对其进行保护生物学的研究已十分迫切。地卷属11种地衣具有不同的海拔分布规律,这些分布规律与各自分布的海拔区间有关。基于11物种的海拔分析支持Rapoport法则。全球暖化对4种地衣的潜在威胁尤其强烈,即：大陆地卷Peltigera continentalis、长孢地卷P. dolichospora、克氏地卷P. kristinssonii和小地卷P. venosa。     

Role of environmental and spatial processes in structuring anuran communities across a tropical rain forest

This study aimed to evaluate if anuran species distributions in riparian and non‐riparian areas are influenced by environmental factors (i.e. niche) and/or by spatial factors (i.e. dispersal). The environmental variables analysed were altitude, distance from the stream and leaf litter depth. Spatial factors were represented by the eigenvectors extracted from geographical coordinates by eigenfunction analysis. The study was conducted in 24 km² of terra‐firme forest in Central Amazonia, Manaus – Amazonas, Brazil. Between November 2008 and May 2009, three samples were taken from 41 plots, 21 plots being placed at non‐riparian areas and another 20 placed in riparian areas. We submitted the assemblage dataset to a partial redundancy analysis to evaluate the contributions of environmental and spatial variables (selected with a forward selection procedure). In addition, we tested if communities differ from riparian and non‐riparian areas using a db‐MANOVA. Species richness and species composition differed between riparian and non‐riparian plots. Some species were restricted to riparian areas. Altitude was the only significant variable (P = 0.005) explaining 21% of the total variance. When analysing the data from all plots using the partial redundancy analysis, 27% of the variance was explained by spatial and environmental variables. The environmental variables explained exclusively 4% of the variance in assemblage composition, and 13% was explained by environmental variables that were also structured in space (i.e. the shared fraction), while 10% was explained exclusively by spatial variables. In conclusion, our results showed differences between the assemblages of riparian and non‐riparian areas which can be explained by the distribution of anuran species along environmental gradients altitude and distance to streams, with little evidence of dispersal limitation.     

广西猫儿山地区鸟类组成及垂直分布格局

猫儿山是华南地区的最高峰,为了了解其鸟类随着海拔高度变化的规律,利用网捕法和样线法对猫儿山地区的鸟类组成及分布格局进行了研究。结果表明,猫儿山地区共有鸟类268种,隶属于16目51科,其中留鸟130种,夏候鸟51种,冬候鸟15种,旅鸟72种。依据不同海拔的典型植被类型把猫儿山地区分成7类生境,其中低海拔的农田生境鸟类多样性最丰富,有156种。随着海拔的升高,猫儿山鸟类种数逐渐减少,G-F指数也表现相似的规律。猫儿山鸟类在区系组成上主要以东洋界鸟类为主,在181种繁殖鸟中,东洋界鸟类有149种,古北界鸟类有15种,其余为广布种。随着海拔的升高,东洋界的鸟类所占的比例逐渐降低,而古北界的鸟类所占的比例逐渐升高。猫儿山鸟类组成的垂直分布格局的形成是多种因素共同作用的结果。     

The phytoplankton along a pollution gradient in the river Mahanadi (M.P. state) India – a multivariate approach

Phytoplankton of the River Seonath, a major tributary of Mahanadi river system, was studied for 15 months together with physical–chemical variables in relation to a pollution gradient. Multivariate analysis and ordination by Principal Components Analysis of the physical–chemical variables and phytoplankton density indicated a community replacement along a pollution gradient. The dominant benthic diatom community, mainly comprising Achnanthes trigibba and A. affinis of the upstream was replaced by Chlorophycea at the middle stretch and Cyanophycea at the downstream sites. Chlorella, Scenedesmus and Coelastrum dominated among Chlorophyceae in the middle stretch in the highly polluted sites, followed by the Cyanophycean assemblage of Microcystis and Merismopedia.     

Prediction of formic acid chromatogram in gradient elution chromatography

Optimal operation in chromatography is needed to save operation time and the solvent used in multiple chromatographic runs. To this end, many simulation studies of chromatography process have been performed. The relationship between the distribution coefficient and the ionic strength is important in gradient elution ion chromatography. Experimental runs and computer simulation were carried out under linear gradient elution conditions in order to compare the experiments and the simulation. Experiments were performed with formic acid under isocratic conditions to determine the simulation equation parameters. Computer simulation was based on three equations which related distribution with ionic strength as follows;K=αI ^−β, K=A+BI+Cl² and. The effects of gradient slope on the chromatograms are discussed, and good agreement between the experimental and the simulated results is shown.     

Do metacommunity theories explain spatial variation in fish assemblage structure in a pristine tropical river?

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Neotropical C3/C4 grass distributions – present,past and future

Changes in C₄ grass distribution and abundance are frequently observed in Quaternary, Holocene and future environmental‐change scenarios. However, the factors driving these dynamics are not fully understood, and conflicting theories have been reported. In this paper, we present a very large dataset of modern altitudinal distribution profiles of C₃ and C₄ grasses covering the entire Neotropical Andes, which was compared with actual climate data. The results of multivariate analysis demonstrate that, in the Neotropical Andes, mean annual temperature is the main factor governing the modern altitudinal distribution of C₃ and C₄ grass species. The C₃ and C₄ grass distributions were compared with simulations based on the Lund‐Potsdam‐Jena dynamic global vegetation model (LPJ‐DGVM), which allowed the present grass distribution to be estimated. Finally, the DGVM was employed to simulate past and future scenarios, using the IPCC's climate projections for 2100 and PMIP2 models for the Holocene Optimum (HO, 6000 years bp ) and the Last Glacial Maximum (LGM, 21 000 years bp ). The results were found to be significantly different from those obtained using a simple photosynthetic model. According to LPJ forced with the PMIP2 models for the LGM, during the LGM, the C₄ grasses would not have reached higher altitudes than found in the present day.     

3种高山植物的物候和种群分布格局在融雪梯度上的变化

在青藏高原东部的一个高山雪床,沿着融雪梯度分别设置早融、中间和晚融3个融雪部位,然后测定川西小黄菊（Pyrethrum tatsienense）、长叶火绒草（Leontopodium longifolium）和圆穗蓼（Polygonum macrophyllum）在3个融雪部位上的物候差异以及种群分布格局的变化。结果表明：从早融到晚融的梯度上,3个物种的物候期都不同程度地有所推迟。其中,开始生长的时间推迟12~14 d,始花期推迟6~8 d,盛花期推迟6 d左右,但同一种植物在不同的融雪部位上的衰老枯黄期趋于一致,这标志着在晚融部位同一植物的生长期要缩短。在种群层次上,长叶火绒草和圆穗蓼的分布格局随着融雪的推迟都发生了一定的变化,基本上表现为从早融部位的集群分布到中间或晚融部位的随机分布。川西小黄菊在各个融雪部位上都表现为集群分布,但集群的强度随融雪的推迟逐渐减弱。     

Global patterns of diversity and community structure in marine bacterioplankton

Because of their small size, great abundance and easy dispersal, it is often assumed that marine planktonic microorganisms have a ubiquitous distribution that prevents any structured assembly into local communities. To challenge this view, marine bacterioplankton communities from coastal waters at nine locations distributed world-wide were examined through the use of comprehensive clone libraries of 16S ribosomal RNA genes, used as operational taxonomic units (OTU). Our survey and analyses show that there were marked differences in the composition and richness of OTUs between locations. Remarkably, the global marine bacterioplankton community showed a high degree of endemism, and conversely included few cosmopolitan OTUs. Our data were consistent with a latitudinal gradient of OTU richness. We observed a positive relationship between the relative OTU abundances and their range of occupation, i.e. cosmopolitans had the largest population sizes. Although OTU richness differed among locations, the distributions of the major taxonomic groups represented in the communities were analogous, and all local communities were similarly structured and dominated by a few OTUs showing variable taxonomic affiliations. The observed patterns of OTU richness indicate that similar evolutionary and ecological processes structured the communities. We conclude that marine bacterioplankton share many of the biogeographical and macroecological features of macroscopic organisms. The general processes behind those patterns are likely to be comparable across taxa and major global biomes.     

森林植被中优势种的形成和分布规律及其应用

一森林多是天然植被(人工林除外),它经历了千百年的演化,在改造环境和适应环境过程中,形成了物种与外界环境的高度吻合,最后形成了多种稳定的森林植被类型,因而研究森林植被中优势种的形成和分布规律,较之农田生态系统等人工植被具有更多的便利条件。森林树种的分布遵循着一定的规律,搞清     

Longitudinal and Vertical Spatial Gradients in the Distribution of Fish within a Canyon‐shaped Reservoir

The large‐scale spatial distribution of fish was investigated within a morphometrically simple canyon‐shaped reservoir with a single major tributary and a longitudinal trophic gradient (Římov Reservoir, Czech Republic). Samples of fish were taken by Nordic survey gill nets (several mesh sizes from 8 to 70 mm knot to knot) installed as surface nets at several offshore areas located along the longitudinal axis of the reservoir. Surveys were carried out in late summer during 1999–2003. An obvious distribution gradient of fish was revealed along the longitudinal axis of the Římov Reservoir. The total relative fish abundance and biomass (catch per unit effort) decreased considerably from the upstream end of the reservoir toward the dam. Roach (Rutilus rutilus), bleak (Alburnus alburnus) and bream (Abramis brama) comprised the bulk of catches at all areas. Enhanced dominance of bream was observed in the fish assemblage at the uppermost, more eutrophic area of the reservoir. The highest number of fish species and the highest abundance of young‐of‐the‐year fish were also observed in the tributary area. In the downstream part of the reservoir, gill net surveys along the vertical depth profiles indicated that offshore fish occupied mostly the epilimnion. Extreme flood events affected the Římov Reservoir, however, it seemed they had no significant impact on the gradients described. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Diversity and vertical distribution of magnetotactic bacteria along chemical gradients in freshwater microcosms

The vertical distribution of magnetotactic bacteria along various physico-chemical gradients in freshwater microcosms was analyzed by a combined approach of viable cell counts, 16S rRNA gene analysis, microsensor profiling and biogeochemical methods. The occurrence of magnetotactic bacteria was restricted to a narrow sediment layer overlapping or closely below the maximum oxygen and nitrate penetration depth. Different species showed different preferences within vertical gradients, but the largest proportion (63-98%) of magnetotactic bacteria was detected within the suboxic zone. In one microcosm the community of magnetotactic bacteria was dominated by one species of a coccoid "Alphaproteobacterium", as detected by denaturing gradient gel electrophoresis in sediment horizons from 1 to 10 mm depth. Maximum numbers of magnetotactic bacteria were up to 1.5 x 10(7) cells/cm3, which corresponded to 1% of the total cell number in the upper sediment layer. The occurrence of magnetotactic bacteria coincided with the availability of significant amounts (6-60 microM) of soluble Fe(II), and in one sample with hydrogen sulfide (up to 40 microM). Although various trends were clearly observed, a strict correlation between the distribution of magnetotactic bacteria and individual geochemical parameters was absent. This is discussed in terms of metabolic adaptation of various strains of magnetotactic bacteria to stratified sediments and diversity of the magnetotactic bacterial communities.     

Community composition and tree population structure in a sub-tropical broad-leaved forest along a disturbance gradient

Floristic composition, diversity, dominance and distribution pattern of species and tree population structure were studied in three stands of a sub-tropical wet hill broad-leaved forest of Meghalaya, India, along a disturbance gradient. Tree species diversity declined with increasing disturbance. Disturbed stands showed low equitability or high dominance and the undisturbed stand exhibited high equitability or low dominance. Contagious distribution among the tree species increased with increasing intensity of disturbance. Species showing regular distribution were restricted only to the undisturbed stand. Effect of disturbance on tree population structure was analysed using density-diameter curves. In the disturbed stands tree species showed reverse J-shaped and/or negative exponential curves, while those in the undisturbed stand exhibited sigmoid to bimodal mound shaped curves.     

The effect of hydropower on fish stocks: comparison between cascade and non-cascade reservoirs

Spatial distributions of fish were studied in two types of reservoirs by means of hydroacoustics during the summer. Different patterns of fish distribution were found in non-cascade (Římov, Želivka) and cascade (Kamyk, Slapy, Štěchovice, Vrané) reservoirs. Maximum biomass and density of fish were observed in the tributary area of the non-cascade reservoir. The biomass declined towards the dam area. Average weight of fish showed the opposite trend—maximum average weight was observed in the dam area and declined towards the tributary area. In the cascade reservoirs fish distribution was found to be more complicated but the maximum biomass and density of fish were observed in the dam areas, whereas the tributary areas were nearly fishless. Poor ecohydrological conditions in the tributaries of cascade reservoirs are likely to be responsible for the low abundance of fish in these areas. This was evident in the example of Vrané reservoir which has two major inflows. Low biomass and density of fish were observed in the cold and low oxygen saturated inflowing cascade Vltava River while higher biomass and density were observed in the warm and well oxygen saturated Sázava River inflow. Average weights of fish followed the same trend as in non-cascade reservoirs—the maximum was in the dam area and it declined towards the tributary area. The vertical distribution of fish is driven by the fully developed stratification of temperature and oxygen during the summer season in non-cascade reservoirs. A significantly lower biomass of fish was observed below the thermocline in vertical surveys in both non-cascade and cascade reservoirs. Summer stratification in cascade reservoirs is weakly developed or is not developed at all due to hypolimnetic releases of cold water and short retention times. High transparency suggests lower primary production in cascade reservoirs. Guest editors: R. L. Welcomme & G. Marmulla Hydropower, Flood Control and Water Abstraction: Implications for Fish and Fisheries     

Ontogenetic variation in habitat associations for four flatfish species in the Gulf of Maine-Georges Bank region

Multivariate ordination techniques were used to examine how size classes of four flatfish species, American plaice Hippoglossoides platessoides , winter flounder Pseudopleuronectes americanus , yellowtail flounder Limanda ferruginea and fourspot flounder Paralichthys oblongus , are related to bottom depth, bottom temperature, substratum grain size and temporal factors using a 35 year time series from autumn and spring in the Gulf of Maine-Georges Bank region. Depth had the most explanatory value during both seasons in most cases, with fish size generally increasing with depth. One exception was yellowtail flounder in the spring for which a temporal factor explained the most variance, reflecting an increase in size over the time series due to changes in fishing pressure. Temperature was secondarily important for yellowtail flounder in the autumn and for fourspot flounder in both seasons. Substratum type was secondarily important for winter and yellowtail flounders in the spring with smaller fish associated with larger substratum types. Seasonal associations with depth, temperature and substratum are related to seasonal spawning migrations, thermal preferences and other ecological factors.     

Community of small mammals along an elevational gradient in Biological Reserve of Serra do Japi,municipality of Jundiaí‐SP,Brazil

Studies of elevational gradients in forests are particularly interesting for the considerable differences that can be observed over short distances, such as in vegetation and temperature. Different taxonomic groups display varying types of distribution patterns along elevational gradients, with unimodal distribution being recognised as the most common pattern. The distribution of species can be affected by a range of factors that include, biotic, spatial, climatic, historic and energetic. Small mammals represent an ideal model for studies about distribution and habitat use as they can be highly abundant, tend to have different diets and use space differently. The aims of this study are to build a comprehensive understanding of the community of small mammals of the Biological Reserve of Serra do Japi and to explore its distribution pattern along elevational gradients. We investigated the influence of biomass of arthropods, fruits and seeds and percentage of ground cover, canopy cover and vertical vegetation at richness and abundance of small mammals at three different elevations. To accomplish this, we used seventy‐two pitfall traps of 63 L to capture small mammals and distributed them equally across three elevations defined as low (880–899 m), intermediate (1046–1089 m) and high (1170–1189 m). Each elevation had three lines or replicas of traps. Throughout the study, we captured one hundred and fourteen individuals belonging to eleven species of small mammals. The presence of rare and endemic species demonstrates the importance of conservation and maintenance of the Biological Reserve of Serra do Japi. In regard to the distribution of species, despite the short gradient range, we found a unimodal pattern and a positive correlation between ground cover (fallen twigs and branches up to 1 m high) and richness and abundance of small mammals. More ground cover can reduce the effects of competition and predation on small mammals’ communities. Abstract in Portuguese is available with online material.