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471.
Limitations of Biodiversity Databases: Case Study on Seed-Plant Diversity in Tenerife, Canary Islands 总被引:3,自引:0,他引:3
Abstract: Databases on the distribution of species can be used to describe the geographic patterns of biodiversity. Nevertheless, they have limitations. We studied three of these limitations: (1) inadequacy of raw data to describe richness patterns due to sampling bias, (2) lack of survey effort assessment (and lack of exhaustiveness in compiling data about survey effort), and (3) lack of coverage of the geographic and environmental variations that affect the distribution of organisms. We used a biodiversity database (BIOTA-Canarias) to analyze richness data from a well-known group (seed plants) in an intensively surveyed area (Tenerife Island). Observed richness and survey effort were highly correlated. Species accumulation curves could not be used to determine survey effort because data digitalization was not exhaustive, so we identified well-sampled sites based on observed richness to sampling effort ratios. We also developed a predictive model based on the data from well-sampled sites and analyzed the origin of the geographic errors in the obtained extrapolation by means of a geographically constrained cross-validation. The spatial patterns of seed-plant species richness obtained from BIOTA-Canarias data were incomplete and biased. Therefore, some improvements are needed to use this database (and many others) in biodiversity studies. We propose a protocol that includes controls on data quality, improvements on data digitalization and survey design to improve data quality, and some alternative data analysis strategies that will provide a reliable picture of biodiversity patterns. 相似文献
472.
473.
水环境中痕量重金属生物活性形态的分析 总被引:6,自引:0,他引:6
水环境中痕量重金属的生物活性形态,包括生物可吸收态和生物毒性形态,这种形态的分析是重金属形态分析研究的一个重要发展方向。对于水环境中重金属对生物的毒害现状评价、潜在危害预测以及水环境容量的确定、排放标准和污染治理方案的制定,具有重要意义。本文总结了各种物理化学法重金属形态分析的结果与生物测试重金属形态测定结果之间的相关性,进而探讨了应用物理化学方法进行金属生物活性形态分析的可行性和特点。 相似文献
474.
聚合氯化铝中Alb和Al13的形态分布规律 总被引:4,自引:0,他引:4
按三类典型工业聚合氯化铝的生产条件制得铝浓度为2.50mol·l^-1,盐基度为0%-92%的A,C,D系列样品,同时采用慢速滴碱法制得铝浓度为0.150mol·l^-1-0.336mol·l^-1,盐基度为0%-92%的B系列聚合氯化铝.Ferron试验结果表明:相同盐基度不同系列样品的Alb值大小变化规律为:盐基度等于20%时,C〉D〉A〉B;盐基度等于30%时,A〉D〉B〉C;盐基度大于30%时,B〉A〉D〉C;四个系列样品的Ala均随盐基度的升高而减小,Alc则随盐基度的升高而增加.27A1-NMR测试结果表明:四个系列所有样品的Al单均随盐基度的升高而减小;相同盐基度的不同系列样品Al13值大小顺序为B〉A〉C〉D;A,C,D系列样品的Al其他均随盐基度的升高而增加,B系列样品的Al其他则先随盐基度的升高而增加,达到最大值后开始降低,然后再开始上升,最大值为B4样品的44.40%.A,C,D三个工业系列样品中的Alb和Al13的绝对值均不大,在所研究的盐基度范围内Alb和Al13均不是其中的优势形态.B系列样品在盐基度大于60%时,Alb和Al13成为其中的优势形态. 相似文献
475.
Using Niche-Based Models to Improve the Sampling of Rare Species 总被引:7,自引:0,他引:7
ANTOINE GUISAN†† OLIVIER BROENNIMANN ROBIN ENGLER MATHIAS VUST NIGEL G. YOCCOZ† ANTHONY LEHMANN§ NIKLAUS E. ZIMMERMANN‡ 《Conservation biology》2006,20(2):501-511
Abstract: Because data on rare species usually are sparse, it is important to have efficient ways to sample additional data. Traditional sampling approaches are of limited value for rare species because a very large proportion of randomly chosen sampling sites are unlikely to shelter the species. For these species, spatial predictions from niche-based distribution models can be used to stratify the sampling and increase sampling efficiency. New data sampled are then used to improve the initial model. Applying this approach repeatedly is an adaptive process that may allow increasing the number of new occurrences found. We illustrate the approach with a case study of a rare and endangered plant species in Switzerland and a simulation experiment. Our field survey confirmed that the method helps in the discovery of new populations of the target species in remote areas where the predicted habitat suitability is high. In our simulations the model-based approach provided a significant improvement (by a factor of 1.8 to 4 times, depending on the measure) over simple random sampling. In terms of cost this approach may save up to 70% of the time spent in the field. 相似文献
476.
Using Economic and Regulatory Incentives to Restore Endangered Species: Lessons Learned from Three New Programs 总被引:2,自引:0,他引:2
Abstract: We studied three new incentive-based programs for restoring endangered species on private lands in the United States: safe harbor, Environmental Defense's Landowner Conservation Assistance Program, and conservation banking. For each program, we gathered data on the number of participating landowners, the number of species targeted for assistance, and the cumulative acreage of enrolled land. Measured in this way, both safe harbor and the Landowner Conservation Assistance Program have been remarkably successful. Landowners are drawn to three aspects of these programs: (1) the removal of regulatory burdens associated with attracting endangered species to their property; (2) technical guidance on how to restore habitats for endangered species; and (3) cost-share assistance for habitat restoration. Technical guidance appears to be more important than either regulatory relief or financial assistance in securing the cooperation of some landowners. Assessing the success or failure of conservation banking proved more difficult, given the relatively small number of banks created to date and the lack of any centralized database on them. However, nearly half of the 47 endangered-species conservation banks we surveyed have sold credits, indicating some success in either acquiring or restoring essential habitats. 相似文献
477.
Biotic Impoverishment and Homogenization in Unfragmented Forest Understory Communities 总被引:11,自引:0,他引:11
THOMAS P. ROONEY SHANNON M. WIEGMANN DAVID A. ROGERS D. M. WALLER 《Conservation biology》2004,18(3):787-798
Abstract: Ecological change is often hard to document because of a lack of reliable baseline data. Several recent then-versus-now surveys of temperate forest and grassland communities demonstrate losses of local plant species, but most are based on data from a single site. We resurveyed understory communities in 62 upland forest stands in northern Wisconsin (U.S.A.) for which quantitative baseline data exist from 50 years ago. These stands are within a largely unfragmented region but vary in species composition and successional stage. We collected data on changes in (1) total and native species richness, (2) the ratio of exotic to native species, (3) the relative abundance of habitat generalists, and (4) community similarity among sites. We also compared how these rates of change varied over time. Over the past 50 years, native species density declined an average of 18.5% at the 20-m2 scale, whereas the ratio of exotic species to native species increased at 80% of all sites. Habitat generalists increased, and habitat specialists declined, accounting in part for an 8.7% rise in average similarity in species composition among sites. Most of these changes cannot be related to succession, habitat loss, or invasion by exotic species. Areas without deer hunting showed the greatest declines in native species density, with parks and research natural areas faring no better than unprotected stands. Animal-pollinated and animal-dispersed species also declined, particularly at unhunted sites. These results demonstrate the power of quantitative multistand data for assessing ecological change and identify overabundant deer as a key driver of community change. Because maintaining forest habitats alone fails to preserve plant diversity at local scales, local biotic simplification seems likely to continue in the region unless active efforts are taken to protect diversity. 相似文献
478.
高寒小嵩草草甸种子库和种子雨动态分析 总被引:18,自引:0,他引:18
对小嵩草草甸种子库的大小和物种组成及与种子雨、地上植被的关系进行了初步研究 .结果表明 ,返青期和枯黄期小嵩草草甸种子库单位体积 (1.0m× 1.0m× 0 .1m)分别有种子nf=10 5 5 0粒和nk=13 815粒 ,分别由 2 2种和 2 4种植物组成 ,分属 9个科 .其中 ,莎草科、豆科和龙胆科占优势 ,禾本科所占比例较小 .每平方米种子雨nr=8436 .4粒 ,由2 5种植物组成 ,分属 10个科 ,莎草科和禾本科所占比例较大 .种子库和种子雨在物种组成上有一定的相似性 (r =0 .76 0 0 ,P <0 .0 1) ,二者共有 19个种 ,分别占种子库和种子雨物种总数的 82 .6 1%和 90 .48% .地上植被与种子库的相似性较小 ,地上植被中有 43.2 4%和 5 1.35 %的植物分别在返青期和枯黄期种子库中出现 ,6 0 %的植物出现于种子雨中 .在物种分布和优势度上 ,地上植被与种子雨间一致性较高 ,但它们与种子库间有一定的分歧 .从地上植被到返青期时的种子库 ,物种多样性降低了 1.6 1% ,从而说明种子库不仅是地上植被补充更新的源泉之一 ,而且是维持植物物种多样性的一种机制 .图 3参 13 相似文献
479.
Binary matrices originating from presence/absence data on species (rows) distributed over sites (columns) have been a subject of much controversy in ecological biogeography. Under the null hypothesis that every matrix is equally likely, the distributions of some test statistics measuring co-occurrences between species are sought, conditional on the row and column totals being fixed at the values observed for some particular matrix. Many ad hoc methods have been proposed in the literature, but at least some of them do not provide uniform random samples of matrices. In particular, some swap algorithms have not accounted for the number of neighbors each matrix has in the universe of matrices with a set of fixed row and column sums. We provide a Monte-Carlo method using random walks on graphs that gives correct estimates for the distributions of statistics. We exemplify its use with one statistic. 相似文献
480.
山西云顶山亚高山草甸优势种群和群落的格局分析 总被引:10,自引:0,他引:10
应用DCA排序与双项轨迹方差法相结合的方法,对云顶山亚高山草甸优势种群和群落的分布格局进行了分析.结果表明,群落格局与其优势种的格局关系密切,披针苔草 车前群系、披针苔草 蒲公英群系和嵩草 车前群系的格局差异明显,种群和群落的分布格局不仅受种的生物学特性影响,还受环境因子制约.图4表1参19 相似文献