全文获取类型
收费全文 | 125篇 |
免费 | 25篇 |
国内免费 | 16篇 |
出版年
2023年 | 5篇 |
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 11篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 8篇 |
2014年 | 15篇 |
2013年 | 7篇 |
2012年 | 8篇 |
2011年 | 5篇 |
2010年 | 7篇 |
2009年 | 14篇 |
2008年 | 4篇 |
2007年 | 4篇 |
2006年 | 11篇 |
2005年 | 8篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有166条查询结果,搜索用时 15 毫秒
1.
群落均匀度分形分析 总被引:7,自引:1,他引:6
修正了Frontier和Ricotta等关于有效物种丰富度指数A与物种丰富度指数S之间幂律关系的定义.探讨了A与S之间分形关系的生态学意义.认为分形维数D是群落均匀度测度值在物种数S不断增加的过程中.向其逼近的一个理论值;提出了利用双对数坐标上建立的A与S拟合直线的方程.对群落均匀度的4种变化趋势进行描述的方法。以广东黑石顶自然保护区森林演替系列为例.研究了针阔叶混交林和常绿阔叶林样带上.随着样带观察长度的逐渐增加群落均匀度的变化情况。结果表明.230m长的混交林样带只存在一个线性无标度区间.群落均匀度随样带长度的不断增加而逐渐降低.向分形维数D=0.810趋近。170m长的常绿阔叶林样带存在两个线性无标度区问.在0~25m的尺度域内.随着样带长度的逐渐增加均匀度不断降低.向分形维数D=0.525逼近;在30~170m的尺度域内.随着样带观察长度的增加.群落均匀度也逐渐增加.向分形维数D=0.920趋近。 相似文献
2.
3.
Carlo Ricotta 《Ecology and evolution》2017,7(13):4835-4843
The amount of variation in species composition among sampling units or beta diversity has become a primary tool for connecting the spatial structure of species assemblages to ecological processes. Many different measures of beta diversity have been developed. Among them, the total variance in the community composition matrix has been proposed as a single‐number estimate of beta diversity. In this study, I first show that this measure summarizes the compositional variation among sampling units after nonlinear transformation of species abundances. Therefore, it is not always adequate for estimating beta diversity. Next, I propose an alternative approach for calculating beta diversity in which variance is substituted by a weighted measure of concentration (i.e., an inverse measure of evenness). The relationship between this new measure of beta diversity and so‐called multiple‐site dissimilarity measures is also discussed. 相似文献
4.
Biocomplexity theory is becoming increasingly important in understanding natural vegetation dynamics and interrelation among all components of the ecosystem. In this study, based on the field investigation of plant species and environmental factors (altitude, microtopography, soil water content, and soil nutrients) in an arid valley of the upper reaches of Minjiang River, Sichuan Province, southwestern China, plant community complexity and its relationship with environmental factors, community diversity, species evenness and richness were studied. Both total and structural complexities of the communities showed a “high- low-high” tendency with the increase in altitude of the area, which meant that the complexity of communities was the highest at the sites of low and high altitude, whereas it was the lowest at the sites of intermediate altitude. It was found that the total community complexity had significant quadratic correlations with soil organic matter (SOM) content, total nitrogen (N), hydrolyzable N, soil water content, and available potassium (K), whereas it had no significant correlations with soil total K, total phosphorus (P), available P, and pH value. The total community complexity positively correlated with community diversity, species evenness and species richness, whereas the structural complexity negatively correlated with the community evenness. Of the two components of the total community complexity, namely, the structural complexity and the structural diversity, the structural complexity was more sensitive than the structural diversity to the changes of species in the community, which was not only related to the community evenness but also to the community richness. The relative contribution of both the structural complexity and the structural diversity to the total complexity would be different for different study areas or ecosystems. 相似文献
5.
Svensson JR Lindegarth M Jonsson PR Pavia H 《Proceedings. Biological sciences / The Royal Society》2012,279(1736):2163-2170
The intermediate disturbance hypothesis (IDH) and the dynamic equilibrium model (DEM) are influential theories in ecology. The IDH predicts large species numbers at intermediate levels of disturbance and the DEM predicts that the effect of disturbance depends on the level of productivity. However, various indices of diversity are considered more commonly than the predicted number of species in tests of the hypotheses. This issue reaches beyond the scientific community as the predictions of the IDH and the DEM are used in the management of national parks and reserves. In order to compare responses with disturbance among measures of biodiversity, we used two different approaches of mathematical modelling and conducted an extensive meta-analysis. Two-thirds of the surveyed studies present different results for different diversity measures. Accordingly, the meta-analysis showed a narrow range of negative quadratic regression components for richness, but not evenness. Also, the two models support the IDH and the DEM, respectively, when biodiversity is measured as species richness, but predict evenness to increase with increasing disturbance, for all levels of productivity. Consequently, studies that use compound indices of diversity should present logical arguments, a priori, to why a specific index of diversity should peak in response to disturbance. 相似文献
6.
7.
Drivers of temporal changes in temperate forest plant diversity vary across spatial scales 下载免费PDF全文
Markus Bernhardt‐Römermann Lander Baeten Dylan Craven Pieter De Frenne Radim Hédl Jonathan Lenoir Didier Bert Jörg Brunet Markéta Chudomelová Guillaume Decocq Hartmut Dierschke Thomas Dirnböck Inken Dörfler Thilo Heinken Martin Hermy Patrick Hommel Bogdan Jaroszewicz Andrzej Keczyński Daniel L. Kelly Keith J. Kirby Martin Kopecký Martin Macek František Máliš Michael Mirtl Fraser J.G. Mitchell Tobias Naaf Miles Newman George Peterken Petr Petřík Wolfgang Schmidt Tibor Standovár Zoltán Tóth Hans Van Calster Gorik Verstraeten Jozef Vladovič Ondřej Vild Monika Wulf Kris Verheyen 《Global Change Biology》2015,21(10):3726-3737
Global biodiversity is affected by numerous environmental drivers. Yet, the extent to which global environmental changes contribute to changes in local diversity is poorly understood. We investigated biodiversity changes in a meta‐analysis of 39 resurvey studies in European temperate forests (3988 vegetation records in total, 17–75 years between the two surveys) by assessing the importance of (i) coarse‐resolution (i.e., among sites) vs. fine‐resolution (i.e., within sites) environmental differences and (ii) changing environmental conditions between surveys. Our results clarify the mechanisms underlying the direction and magnitude of local‐scale biodiversity changes. While not detecting any net local diversity loss, we observed considerable among‐site variation, partly explained by temporal changes in light availability (a local driver) and density of large herbivores (a regional driver). Furthermore, strong evidence was found that presurvey levels of nitrogen deposition determined subsequent diversity changes. We conclude that models forecasting future biodiversity changes should consider coarse‐resolution environmental changes, account for differences in baseline environmental conditions and for local changes in fine‐resolution environmental conditions. 相似文献
8.
Diversity, abundance or rare species as a target for the conservation of mammalian carnivores: a case study in Southern Spain 总被引:6,自引:2,他引:4
Alejandro Travaini Miguel Delibes Pablo Ferreras Francisco Palomares 《Biodiversity and Conservation》1997,6(4):529-535
Management goals in protected areas and/or communities usually include diversity as one of the most valuable and confident criteria. Nevertheless, the use of diversity and related indices as a means of evaluating successful management practices could produce conflicting results. Here we report a case study in one of the most important European protected areas. After 6 years of intensive conservation management of the Don~ana National Park, the general abundance and numbers of the target single-species conservation plan (the Iberian lynx) increased, although carnivore community diversity and evenness decreased. This was a result of a disproportionate increase of an oportunistic native species, the red fox. We propose the combined use of diversity, richness and evenness indices when monitoring management practices such as those reported here. 相似文献
9.
An arctic river was fertilized continuously through the ice-free season with phosphoric acid beginning in 1983. The epilithic
diatom community increased in biomass in the first two years in response to the added limiting nutrient (Peterson et al., 1983). The diatom community switched from one dominated by Hannea arcus to one dominated by species of Achnanthes and Cymbella. The immediate responses to the P-addition were decreases in both
the Shannon diversity and evenness indices. By the second year, the community diversity increased downriver reaching maximal
species richness (110–127 spp). In 1985–1987, the epilithic algal biomass decreased an order of magnitude with both whole-river
PO4 (1985, 1987) and PO4 + NH4 addition (1986). In the 5th summer of fertilization, the reduction in biomass was clearly caused by a numerical increase
of grazing, refugia-building chironomids (Orthocladiinae, primarily) (Gibeau, 1991; Gibeau, Miller, Hershey, in prep.). We
assume the algal biomass reduction in the 3rd and 4th years was similarly caused by grazers with a two year time lag in the
numerical response of these monovoltine species. The evenness of the community increased in 1986 as if it might have been
grazed; however the number of immigrants was reduced. The community became dominated by Eunotia, Cymbella and Achnanthes,
species either fast growing or more prostrate, as the erect species of Hannea Diatoma, and Fragillaria declined. A detrended
correspondence analysis of the temporal and spatial diatom samples in species space (186 spp.) showed that the largest variation
in the community was between years and less variation was associated with river fertilization.
Samples from bioassay tubes run by Peterson et al. (1983) in the Kuparuk River showed P and N + P limitation as found in the river in 1983–84. Like the river samples, the
largest change in the diatom community occurred between 15 and 25 day samples, more than that induced by fertilization. Diatoms
sampled from all treatments taken at day 25 were more similar to one another than those sampled at day 15. Diatoms colonizing
glass slides used in the bioassay tubes were dominated by Achnanthes linearis and Cymbella minuta. Of the 84 species found in bioassays, 26 species were present in all river samples for 4 years. Differences in the communities
discriminated by multivariate methods were cause by changes in rare species and abundance patterns of common species. 相似文献
10.
A global synthesis of the effects of diversified farming systems on arthropod diversity within fields and across agricultural landscapes 下载免费PDF全文
《Global Change Biology》2017,23(11):4946-4957
Agricultural intensification is a leading cause of global biodiversity loss, which can reduce the provisioning of ecosystem services in managed ecosystems. Organic farming and plant diversification are farm management schemes that may mitigate potential ecological harm by increasing species richness and boosting related ecosystem services to agroecosystems. What remains unclear is the extent to which farm management schemes affect biodiversity components other than species richness, and whether impacts differ across spatial scales and landscape contexts. Using a global metadataset, we quantified the effects of organic farming and plant diversification on abundance, local diversity (communities within fields), and regional diversity (communities across fields) of arthropod pollinators, predators, herbivores, and detritivores. Both organic farming and higher in‐field plant diversity enhanced arthropod abundance, particularly for rare taxa. This resulted in increased richness but decreased evenness. While these responses were stronger at local relative to regional scales, richness and abundance increased at both scales, and richness on farms embedded in complex relative to simple landscapes. Overall, both organic farming and in‐field plant diversification exerted the strongest effects on pollinators and predators, suggesting these management schemes can facilitate ecosystem service providers without augmenting herbivore (pest) populations. Our results suggest that organic farming and plant diversification promote diverse arthropod metacommunities that may provide temporal and spatial stability of ecosystem service provisioning. Conserving diverse plant and arthropod communities in farming systems therefore requires sustainable practices that operate both within fields and across landscapes. 相似文献