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511.
Measuring diversity: the importance of species similarity 总被引:4,自引:0,他引:4
Realistic measures of biodiversity should reflect not only the relative abundances of species, but also the differences between them. We present a natural family of diversity measures taking both factors into account. This is not just another addition to the already long list of diversity indices. Instead, a single formula subsumes many of the most popular indices, including Shannon's, Simpson's, species richness, and Rao's quadratic entropy. These popular indices can then be used and understood in a unified way, and the relationships between them are made plain. The new measures are, moreover, effective numbers, so that percentage changes and ratio comparisons of diversity value are meaningful. We advocate the use of diversity profiles, which provide a faithful graphical representation of the shape of a community; they show how the perceived diversity changes as the emphasis shifts from rare to common species. Communities can usefully be compared by comparing their diversity profiles. We show by example that this is a far more subtle method than any relying on a single statistic. Some ecologists view diversity indices with suspicion, questioning whether they are biologically meaningful. By dropping the naive assumption that distinct species have nothing in common, working with effective numbers, and using diversity profiles, we arrive at a system of diversity measurement that should lay much of this suspicion to rest. 相似文献
512.
Resource competition theory predicts that, in equilibrium, the number of coexisting species cannot exceed the number of limiting resources. In some competition models, however, competitive interactions may result in nonequilibrium dynamics, allowing the coexistence of many species on few resources. The relevance of these findings is still unclear, since some assumptions of the underlying models are unrealistic. Most importantly, these models assume that individual growth directly reflects the availability of external resources, whereas real organisms can store resources, thereby decoupling their growth from external fluctuations. Here we study the effects of resource storage by extending the well-known Droop model to the context of multiple species and multiple resources. We demonstrate that the extended Droop model shows virtually the same complex dynamics as models without storage. Depending on the model parameters, one may obtain competitive exclusion, stable equilibrium coexistence, periodic and non-periodic oscillations, and chaos. Again, nonequilibrium dynamics allows for the coexistence of many species on few resources. We discuss our findings in the light of earlier work on resource competition, highlighting the role of luxury consumption, trade-offs in competitive abilities, and ecological stoichiometry. 相似文献
513.
The need to look beyond the production and provision of relief seed: experiences from southern Sudan
Free distribution of seeds in selected areas of southern Sudan has been widespread as a way of increasing food security. Field research in areas targeted for seed relief found that farmer seed systems continue to meet the crop and varietal needs of farmers even following the 1998 famine. Donor investments in seed multiplication of improved sorghum have not been sustained due to a lack of effective demand for the improved seed beyond that created by the relief agencies. The article argues that rather than imposing outside solutions, whether through seed provisioning or seed production enterprises, greater attention needs to be given to building on the strengths of existing farmer systems and designing interventions to alleviate the weaknesses. The case is made to support dynamically the process of farmer experimentation through the informed introduction of new crops and varieties that can potentially reinforce the strength and diversity of local cropping systems. 相似文献
514.
Unsightly and environmentally damaging debris is an ever present problem for waterways and beaches around the world. This debris has numerous sources, and is comprised of materials ranging from metal and wood to plastics and paper. the aesthetic, economic, and environmental impacts of debris have been well documented over the past several years. in an effort to control the release of trash and debris into our waters, there are many activities ongoing in the US. One such activity is a coordinated effort between the US Environmental Protection Agency (EPA), other federal Agencies (National Oceanic and Atmospheric Administration (NOAA), United States Coast Guard (USCG), United States Navy (USN), National Park Service (NPS), Department of Interior (DOI)), industry (the Society of the Plastics Industry, INC. (SPI)), environmental, and local groups. This paper describes the results of field assessments, and the other activities undertaken by EPA as part of this coordinated effort to control the release of debris to our nation's waterways. 相似文献
515.
A new version of a classical method was applied to study the distribution of natural radionuclides (238U, 230Th, and 226Ra) in the soil fractions obtained by a sequential extraction procedure. The potential significance of the fractions obtained with this method was tested on two very similar soils but with very different contents of the three radionuclides, collected in the proximity of a disused uranium mine located in the Extremadura region in the south-west of Spain. The results confirmed that, if only non-residual fractions are considered, the sequential method applied shows a characteristic speciation pattern of these natural radionuclides in this soil matrix, i.e., the distribution of each of the three radionuclides was very similar for the two soil samples. 相似文献
516.
Grimsrud TK Berge SR Martinsen JI Andersen A 《Journal of environmental monitoring : JEM》2003,5(2):190-197
Among workers employed at a nickel refinery in Norway between 1910 and 1977 an elevated risk of lung cancer has been demonstrated. A dose-related effect from nickel exposure has been identified, with the strongest gradient for water-soluble nickel. This pattern was recently confirmed in a nested case-control study with adjustment for smoking and potential occupational confounders. In the present study, updated cancer data were used to explore the risk by duration of work at the refinery and by exposure to different forms of nickel. Comparisons were made with the national male population (standardised incidence ratios) as well as internal reference groups (Poisson regression) under adjustment for age and smoking. The results confirmed earlier findings of a strong dose-related risk dependent on duration of work in production departments and cumulative exposure to nickel, most clearly seen for water-soluble nickel. Only slightly elevated risks were found among the unexposed and in the group with no experience from production or maintenance work. The risk associated with exposure to nickel chloride was similar to that for nickel sulfate. Analyses restricted to men exposed after 1967, with estimates based on personal monitoring of nickel in the breathing zone, showed the same risk pattern as for earlier years. Elevated lung cancer incidence was even suggested for workers with their first employment after 1978 when a lot of high exposure jobs were abandoned. The combined effect of exposure to nickel and smoking seemed to be in agreement with a multiplicative risk pattern. 相似文献
517.
Ashmore J Babister E Corsellis T Fowler J Kelman I McRobie A Manfield P Spence R Vitale A Battilana R Crawford K 《Disasters》2003,27(4):273-287
The diversity of shelters used in transitional settlements for internally displaced persons (IDPs) in Herat, Afghanistan is described. The information is based on a field survey undertaken in March 2002 and highlights the adaptation techniques, which IDPs undertake to improve any provided shelter. Potential areas for improvement are indicated; for example, the possibility for using insulated, demountable liners to prevent cold-related deaths without sacrificing shelter flexibility along with the likely need for better agency coordination of the shelter responses they provide. The wider context in which the technical recommendations would be implemented must also be considered. Such issues include agency resources, political impediments to providing the desired option, and the preference of many IDPs that the best shelter would be their home. 相似文献
518.
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520.
Clive?BonsallEmail author Adina?Boronean? Andrei?Soficaru Kathleen?McSweeney Tom?Higham Nicolae?Miri?oiu Catriona?Pickard Gordon?Cook 《Die Naturwissenschaften》2012,99(4):321-325
In 1968, excavations in the Climente II cave in the Iron Gates gorge of the River Danube in southwest Romania unearthed the skeleton of an adult male. The burial was assumed to be of Late Pleistocene age because of the presence of Late Upper Palaeolithic (LUP) artefacts in the cave. However, there was no strong supporting stratigraphic evidence, and the body position is reminiscent of Early Neolithic burial practice in the region. Here, we report the results of radiocarbon and stable isotope analyses of the Climente II skeleton, which show that the skeleton dates to the Bølling–Allerød Interstadial ~14,500 cal BP. This is several millennia older than any previously dated human remains from the Iron Gates region and confirms its status as the oldest known burial from Romania. The stable isotope results indicate a diet with an emphasis on aquatic resources, contrary to the commonly held view that the LUP inhabitants of the Iron Gates subsisted mainly by hunting large land mammals. 相似文献