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101.
The Science of Nature - 相似文献
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Divergent evolution of feeding substrate preferences in a phylogenetically young species flock of pupfish (Cyprinodon spp.) 总被引:1,自引:0,他引:1
A fundamental question in sympatric speciation is how trophic divergence is achieved. We used an extremely young (<8,000 years)
species flock of pupfish (Cyprinodon spp.) from Laguna Chichancanab in south-eastern Mexico to examine divergent evolution of preferences for different feeding
substrates. In a test aquarium, we presented four feeding substrates (sand, gravel, a plastic plant, and blank bottom), but
no actual food was offered. The four feeding substrates were chosen to mirror the most common substrate types in Laguna Chichancanab.
Previous studies demonstrated that benthic food items prevail in the diet of most Cyprinodon species. C. beltrani preferred sand, whereas C. labiosus preferred gravel. F1 hybrids of both species showed intermediate preferences. C. maya searched for food equally at all substrates. As the test fish were reared under identical laboratory conditions (i.e., in
the absence of feeding substrates), the species-specific preferences appear to be genetically fixed, suggesting rapid divergent
evolution of feeding behaviors. 相似文献
104.
Joachim von Schéele 《International Journal of Green Energy》2013,10(2):139-148
There is a strong political will to decrease CO2 emissions. Although the steel industry only accounts for some 5% of worldwide CO2 emissions (which totalled 1,200 million tonnes per annum in the late 1990s), it will be strongly affected by this. The EU, for example, is putting up strong economic incentives for reductions. This is taking place at a time when demand for steel products is greater than ever. To radically change existing processes and production routes to decrease the CO2 emissions would be extremely expensive, even if it were possible. Nevertheless, many of the solutions which have been discussed seem to go in this direction. The other alternative discussed seems to be the creation of process solutions and alterations that lead to a focusing of CO2 streams, i.e., much higher CO2 concentrations in flue gases than today, for entrapment of the CO2 so that it is not discharged into the atmosphere. These solutions are feasible, but expensive. However, there exists today a number of solutions and technologies which, if fully implemented, could substantially decrease CO2 emissions without seriously altering current methods of operation; they are short-term viable solutions. The present paper reviews and discusses such technologies, throughout the steel production paths. If these solutions are fully implemented, the combined impact on CO2 emissions from the steel industry worldwide is estimated to be a reduction of 100–150 million tonnes of CO2 per annum, i.e., current emissions can be reduced by some 8–10% within a relatively short time span. 相似文献
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A regional-scale study on the crop uptake of cadmium from sandy soils: measurement and modeling 总被引:1,自引:0,他引:1
Plant uptake is one of the major pathways by which cadmium (Cd) in soils enters the human food chain. This study was conducted to investigate the uptake of Cd by crops from soils within the wastewater irrigation area (WIA) of Braunschweig (Germany) and to develop a simple process-oriented model that is suited to predict Cd uptake at the regional scale. The sandy soils within the WIA (4300 ha) have received considerable loads of heavy metals by irrigation using municipal wastewater for up to 40 years. In 1998 and 1999, we sampled soil and plant material at 40 potato (Solanum tuberosum L.), 40 sugar beet (Beta vulgaris L.), and 32 winter wheat (Triticum aestivum L.) fields. In both years and for all three crops, we found close linear relationships between the Cd content of plant material and the Cd concentration in soil solution. For all three crops, we observed a trend of relatively increased Cd uptake in the year with the higher saturation deficit of the atmosphere. We interpret this to indicate that transpiration plays an important role in the Cd uptake of crops under the conditions of the WIA. In modeling the uptake of Cd by crops, we assume that uptake is proportional to mass flow, that is, the product of water transpired, Cd concentration in soil solution, and a plant-specific empirical parameter. The simulations agreed well with the observed Cd contents in crops. Our model explained between 66 and 87% of the observed variance. 相似文献
107.
Entwicklungsphysiologische und genetische Grundlagen der Formbildung bei der Schirmalge Acetabularia 总被引:1,自引:0,他引:1
Joachim Hämmerling 《Die Naturwissenschaften》1934,22(50):829-836
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