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非自治带扩散的Kolmogorov系统的持续生存性 总被引:1,自引:0,他引:1
本文把持续生存的定义推广到n个种群m个缀块间扩散的非自治Kolmogorov系统中去,应用持续生存函数,讨论了系统的一致持续生存性和永久共存性,获得了系统持续生存的几个充分条件,并应用上述结果讨论了具有一生非自治扩散的Lotka-Volterra系统持续生存性。 相似文献
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提出了一个具有时滞的非自治差分竞争系统.分别利用差分不等式及Lyapunov离散函数技巧,得到了系统永久持续生存和正解全局吸引的充分条件.数值模拟验证了理论结果的正确性. 相似文献
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具有分离扩散的两种群Lotka—Volterra模型的持久性 总被引:1,自引:1,他引:0
本文考虑具有分离扩散的捕食-被捕食系统的持续性。此模型由两种群组成,其中被捕食种群可在两个生态环境中生存,而捕食种群仅能在一个生态环境中生存,两种群的动态行为都用Lotka-Volterra模型来描述。得到了系统强持续的充分必要条件,并证明了无论无扩散时系统是共存的,还是主导的都可以适当选择分离扩散系数使整个系统强持续。 相似文献
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食物链长度是生态系统的基本属性,其变化决定着群落结构和生态系统功能。稳定同位素分析技术的进步推进了生态系统中食物链长度决定因子相关研究的开展。尽管近期的研究证明了食物链长度与资源可利用性、生态系统大小、干扰等远因之间的关系,但是对于食物网内部结构变化这一近因对食物链长度的影响作用关注较少。综述了边界明确和开放类型淡水生态系统中食物链长度的相关研究进展;探讨了远因和近因机制在决定食物链长度中的作用;给出了判断不同层次和尺度上决定食物链长度机制的概念框架;为今后更好的开展不同生态系统间食物链长度的比较研究提出了建议。 相似文献
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Persistence-extinction in simple food chains modelled by Lotka-Volterra dynamics is governed by a single parameter which depends
upon the interspecific interaction coefficients, the intraspecific interaction coefficients, and the length of the food chain.
In persistent systems with nonzero carrying capacity, two new features predominate. Trophic level influence factors relate
persistence on different trophic levels and determine, in conjunction with the persistence parameter, the magnitude of persistence.
Equilibrium component ordering, which results in persistent systems, mandates once again that systems need to be studied on
the complete ecosystem level; static field measurements reflect species location in the food chain, the total length of the
food chain and assume characteristics according to these factors. 相似文献
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Ana Milstein 《Hydrobiologia》1992,231(3):177-186
The relationships between cultivated fish species and their environment is largely dependent on the biological characteristics of the fish and the degree of intensification of the culture. In extensive and semi-intensive systems, based on natural production, stocking fish species of different feeding habits together enables a more efficient utilization of pond resources. In polyculture systems only a proper combination of ecologically different species at adequate densities will utilize the available resources efficiently, maximize the synergistic fish-fish and fish-environment relationships and minimize the antagonistic ones. Synergistic interactions among fish species may be explained on the basis of two interrelated processes: increase of food resources and improvement of environmental conditions. Antagonistic interactions occur between incompatible species combinations and when the stocking rates are balanced; in this case, the way the system is affected depends on the food chain level were the imbalance occurs. Several examples of synergism and antagonism at different levels of the food chain are analyzed in this paper. The knowledge of fish-fish and fish-environment quantitative relationships enables choosing adequate combinations of fish species, stocking rates, input types and rates, and other management decisions according to the specific local conditions: climate, quality of water supply and pond fertility, availability of fish fry and fingerlings, availability of feeds and fertilizers, and market requirements. 相似文献
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Robert D. Holt 《Ecological Research》2002,17(2):261-273
Ecologists increasingly recognize that a consideration of spatial dynamics is essential
for resolving many classical problems in community ecology. In the present paper, I argue that understanding how trophic interactions influence population stability can have important implications for the expression of spatial processes. I use two examples to illustrate this point. The first example has to do with spatial determinants of food chain length. Prior theoretical and empirical work has suggested that colonization–extinction dynamics can influence food chain length, at least for specialist consumers. I briefly review evidence and prior theory that food chain length is sensitive to area. A metacommunity scenario, in which each of various patches can have a food chain varying in length (but in which a consumer is not present on a patch unless its required resource is also present), shows that alternative landscape states are possible. This possibility arises if top predators moderate unstable interactions between intermediate predators and basal resources. The second example has to do with the impact of recurrent immigration on the stability of persistent populations. Immigration can either stabilize or destabilize local population dynamics. Moreover, an increase in immigration can decrease average population size for unstable populations with direct density-dependence, or in predator–prey systems with saturating functional responses. These theoretical models suggest that the interplay of temporal variation and spatial fluxes can lead to novel qualitative phenomena. 相似文献
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Smith BG 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2008,363(1492):849-861
This paper reviews the opportunities available for food businesses to encourage consumers to eat healthier and more nutritious diets, to invest in more sustainable manufacturing and distribution systems and to develop procurement systems based on more sustainable forms of agriculture. The important factors in developing more sustainable supply chains are identified as the type of supply chain involved and the individual business attitude to extending responsibility for product quality into social and environmental performance within their own supply chains. Interpersonal trust and working to standards are both important to build more sustainable local and many conserved food supply chains, but inadequate to transform mainstream agriculture and raw material supplies to the manufactured and commodity food markets. Cooperation among food manufacturers, retailers, NGOs, governmental and farmers' organizations is vital in order to raise standards for some supply chains and to enable farmers to adopt more sustainable agricultural practices. 相似文献
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Microbes in food processing technology 总被引:4,自引:0,他引:4
Abstract: There is an increasing understanding that the microbial quality of a certain food is the result of a chain of events. It is clear that the microbial safety of food can only be guaranteed when the overall processing, including the production of raw materials, distribution and handling by the consumer are taken into consideration. Therefore, the microbiological quality assurance of foods is not only a matter of control, but also of a careful design of the total process chain. Food industry has now generally adapted quality assurance systems and is implementing the Hazard Analysis Critical Control Point (HACCP) concept. Rapid microbiological monitoring systems should be used in these cases. There is a need for rapid and simple microbiological tests which can be adapted to the technology and logistics of specific production processes. Traditional microbiological methods generally do not meet these high requirements. This paper discusses the tests, based on molecular biological principles, to detect and identify microbes in food-processing chains. Tests based on DNA technology are discussed, including in vitro DNA amplification like the polymerase chain reaction (PCR) method and identifications based on RFLP, RAPD and DNA fingerprinting analysis. PCR-haled methodology can be used for the rapid detection of microbes in food manufacturing environments. In addition, DNA fingerprinting methods are suitable for investigating sources and routes of microbial contamination in the food cycle. 相似文献
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"蒲公英-蝌蚪-鳝鱼"食物链的物流与能流分析 总被引:1,自引:0,他引:1
本文对食物链“蒲公英—蝌蚪—鳝鱼”的物质流和能量流作了定量分析。结果表明:该食物链经济产品的物质、能量转化效率较低,生物量转化效率为1.1%,能量转化效率为0.8%,N、P转化效率分别为3.1%、1.5%。但该食物链刺激鳝鱼食欲,有利于鳝鱼繁殖。 相似文献
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We show in this paper that the chaotic regimes of many food chain models often enjoy a very peculiar property, known as peak-to-peak dynamics. This means that the maximum (peak) density of the populations of any trophic level can be easily forecasted provided the last two peaks of the same population are known. Moreover, extensive simulation shows that only the last peak is needed if the forecast concerns the population at the top of the food chain and that peaks variability often increases from bottom to top. All these findings bring naturally to the conclusion that top populations should be sampled in order to have higher chances to detect peak-to-peak dynamics. The analysis is carried out by studying ditrophic food chain models with seasonally varying parameters, tritrophic food chain models with constant parameters, and more complex food chain and food web models. 相似文献
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稻草—凤尾菇—蚯蚓—肉鸡食物链的氮流与能流研究 总被引:4,自引:0,他引:4
稻草养菇、菇渣喂蚓、以蚂喂鸡是通过营养关系将三个生产过程有机地连接起来,形成农业生态系统特有的食物链。关于这三个环节各自的经济效益及栽培技术方面的研究工作已经做了很多,而作为一条食物链的整体状况,主要是能流和物流状况。尚未见到更深入具体的报道。作者试图通过实验定量分析和评价该食物链中每一链节上以及整体上的氮流和能流状况,进而对其生产应用价值做一初步探讨。 相似文献
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Global patterns of aquatic food chain length 总被引:5,自引:1,他引:4
Food chain length is a fundamental ecosystem property, and plays a central role in determining ecosystem functioning. Recent advances in the field of stable isotope ecology allow the estimation of food chain length (FCL) from stable nitrogen isotope (δ15 N) data. We conducted a global literature synthesis and estimated FCL for 219 lake, stream, and marine ecosystems. Streams had shorter food chains (∼3.5 trophic levels) than marine and lake ecosystems (∼4.0 trophic levels). In marine systems, inclusion of marine mammals increased FCL by 2/3 of a trophic level. For each ecosystem type, estimates of FCL were normally distributed and spanned two full trophic levels. Comparison with published connectance food webs revealed similar mean FCL values, though stable isotope-derived FCL estimates were less variable. At the global scale, FCL showed weak or no relationships with ecosystem size, mean annual air temperature, or latitude. Our study highlights the utility of stable isotopes for quantifying among-system food web variability, and the application of this approach for assessing global-scale patterns of food chain length. 相似文献