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91.
渤海主要生物种间关系及食物网的研究↑(*) 总被引:24,自引:8,他引:24
根据1992年-1993年渤海增殖生态基础调查大面定点底拖网试捕的渔获物,对渤海27种鱼类和10种虾蟹类的3801个胃含物样品进行了分析,并与10年前渤海鱼类的食性进行了比较。结果表明:蓝点马鲛、小黄鱼和白姑鱼等主要捕食鱼类胃含物中鱼的比例较10年前明显增加,鱼类的食性类型无明显变化。渤海低级肉食性鱼类的营养级由1982-1983年的平均2.4上升为2.5,中、高级肉食性鱼类的营养级分别由原来的平均3.2和3.8降为2.8和3.3。渤海主要鱼类之间饵料重叠系数大于0.6的占15%。鱼为渤海多数中、高级肉食性鱼类的主要摄食对象。 相似文献
92.
We examined collembolan food preference for fungal mycelium grown on copper-contaminated medium, and the relationship between copper content, food selectivity and collembolan fitness when fed contaminated mycelium.To clarify whether collembolan food selectivity is related to fitness parameters, Folsomia candida were fed mycelium of the dark-pigmented fungus Alternaria alternata grown on medium with different copper concentrations. Copper-contaminated food (fungus grown on 50, 125, 250 and 500 μg Cu g−1 medium, fresh wt.) was offered together with untreated food for 4 weeks. F. candida fed selectively on the provided mycelium and discriminated clearly between mycelium grown on high and low levels of contamination, distinctly preferring fungus grown on medium with a total copper concentration of 50 and 125 μg g−1. In contrast, fungus grown on highly contaminated medium (250 and 500 μg g−1) was avoided. Collembolan food preference generally matched fitness parameters. Reproduction was significantly affected by the total copper concentration of the fungal growth medium. When fed their preferred mycelium, collembolan reproduction was enhanced, whereas a diet of highly contaminated mycelium (250 or 500 μg g−1) resulted in a strong decrease in reproduction. Adult survival was affected only marginally. Even though heavy metal contamination is a potential stress factor for many soil microarthropods, F. candida is able to discriminate between high and low quality food sources, and even benefits from moderately elevated copper concentrations. 相似文献
93.
Chemical taxonomy based upon the composition of lipids is widely applied to investigate microbial communities and fatty acids have recently been employed to connect soil microbial and faunal food webs as well as to elucidate functional groups at higher trophic levels. The additional use of compound-specific isotopic analysis of 13C/12C ratios in fatty acids allows assessing specific trophic links and belowground carbon fluxes. In this review systematic patterns and processes underlying variations in the composition of fatty acids and their 13C/12C ratio are described. The emphasis is on biomarker fatty acids, their incorporation and modification, effects of pool size, and analytical methods. Further development of the application of fatty acid profiling to soil ecology should include both advances in experimental research and growth of theory. Accordingly, areas in which future experimentation can lead to progress in soil food web analysis are identified. Overall, combining fatty acid biomarker and their isotopic ratios will allow detailed insight into belowground trophic interactions. 相似文献
94.
Demand for urban allotment plots has recently increased in Portugal but little is known about the characteristics and motivations of the demanding population, and if and how its characteristics affect its motivations.In this article, we use the Municipal Network of Urban Allotment Gardens (MNUAG)1 launched by the Portuguese municipality of Vila Nova de Gaia for an exploratory Case Study research. Based on the data collected in the MNUAG application forms submitted in the period 2012–2013, we describe the characteristics and the motivations of the population demanding for urban allotment gardens (UAG)2 and run a logit model to find if and how the motivations are influenced by the characteristics.The population of applicants to the MNUAG is quite diverse. It has a balanced gender distribution and an average age of 47 years. Most of the applicants are between 25 and 64 years old, and belong to households with 2–4 members.To supplement family budget, occupation of leisure times, and access to organic farming are its most important motivations, followed by environmental concerns, the practice of physical exercise, and education.Motivations are influenced by the characteristics. This study has identified two groups of applicants with contrasting motivations. Food security is the only significant motivation for the unemployed and low-income applicants. Food safety, health concerns, environmental concerns, recreation, and education are common and frequent motivations among the upper and intermediate professional groups.Results can have future implications on the MNUAG, namely on the UAG location and typology, plot number, and plot size. To meet the demand of all the types of applicants, while fostering social cohesion, the municipality should reinforce its current small UAG structure and add to the MNUAG one or two productive parks. 相似文献
95.
[目的]探寻最佳脱氧效果的食品脱氧剂。[方法]对比不同配比的铁系脱氧剂在相同条件下的脱氧效果并比较铁粉活化程度对脱氧效果的影响。[结果]配比为0.3 g活化铁粉、0.1 g硅藻土、1 g Na2CO3.10H2O、0.2 g NaCl时脱氧效果最好。[结论]通过该实验获得了最佳脱氧效果的食品脱氧化剂配比。 相似文献
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1995年-1998年中国连续4年粮食丰收,1999-2001年中国粮食连续3年减产,但粮食库存仍然较多。并不能够扭转转收带来的供大于求的局面,预计2002年粮食增产1.1%,在短期内粮食供给大于需求的买方市场态势不会改变,因此,应充分利用当前时机,调整产业结构,发展肉牛生产,促进农业结构调整是提高农民收入的重要途径。文中还分析了欧盟,日本,韩国等国疫情风波及其原因,提出了中国发展绿色肉牛产销供应链的若干对策。 相似文献