一类扩散的种内相食系统正平衡态的全局渐近稳定性

讨论一类扩散的种内相食的捕食者-食饵模型,该模型带有齐次Neumann边界条件.通过迭代的方法证明:在适当的条件下,该模型唯一正常数平衡解全局渐近稳定.     

一类捕食者与被捕食者模型的持久性与稳定性

研究了一类捕食者与被捕食者模型,该生态系统是一个食饵种群被一个捕食种群捕食.当给定参数满足一定条件下,利用比较原理和构造Lyapunov函数的方法,证明了系统的持久性和全局渐近稳定性,并讨论了正平衡点的渐近稳定性.     

富氢水和富氢生理盐水生物医学研究进展——临床试验

氢分子已被证实具有广泛的生物学效应,研究表明,氢气对多种疾病具有显著的治疗作用。近年来,国内外关于氢分子临床应用的报道较多,为疾病治疗提供了新的途径。饮用富氢水或注射富氢生理盐水是常用的氢气摄入方式,因其摄入简单、安全性高得到了临床广泛地关注。主要综述了富氢水在代谢性疾病、神经系统疾病、炎症性疾病、肿瘤、皮肤病及运动疲劳等的临床研究进展,旨在为富氢水和富氢生理盐水的临床应用及作用机制研究提供理论参考。     

富硒食用菌的研究进展

富硒食用菌是一类有价值的药用/功能性食品.从食用菌的富硒特性、富硒食用菌的营养成分、药理作用及生产技术等方面进行了总结.     

食蚜瘿蚊研究进展

<正> 食蚜瘿蚊Aphidoletes aphidimyza(Rond.)是蚜虫的一种专一捕食性天敌,可以取食61种不同作物上的蚜虫(Harris,1973),其中包括许多种重要的农业害虫。早在1916年,Davis就指出食蚜瘿蚊是蚜虫的一种具有很大潜在价值的生防控制因子。70年代初,联邦德国、苏     

富脯氨酸模体研究进展

综述了近年来富脯氨酸模体的研究进展状况,并将其分为PxxP核心序列模体、聚脯氨酸模体、PPxY核心序列模体以及其他类型的模体4类,论述了富脯氨酸膜体的生物学功能及其常出现的原因.     

昆虫中肠围食膜蛋白研究进展

围食膜是大多数昆虫中肠内壁附着的一层起润滑和保护作用的半透性粘膜, 按其形成方式不同分为Ⅰ型围食膜和Ⅱ型围食膜。围食膜主要由几丁质和蛋白质构成, 其中蛋白质对于维持围食膜的致密结构至关重要, 对围食膜蛋白的破坏可能会对昆虫的正常生长发育造成干扰, 甚至会导致低龄幼虫的死亡。本文介绍了围食膜的组成与结构, 阐述了昆虫围食膜蛋白研究的新发现、并依据结构特征对它们进行了分类, 总结了以围食膜蛋白为新靶标的害虫防治的可能途径, 讨论了当前围食膜蛋白研究的不足, 最后展望了今后围食膜蛋白研究的发展方向。     

富硒畜产品研究进展

综述了硒的生物学功能、居民摄入现状、富集载体选择以及富硒肉、蛋、奶等优质畜产品的国内外研究进展等,并结合该领域目前的发展现状及存在问题,提出我国富硒产业未来的工作重点,为推进我国营养型农业生产、保障国民健康提供科学依据。     

富硒食品的研究进展与展望

介绍了富硒食品中硒元素的优点,总结了富硒产品的分类、国内外富硒食品的研究现状以及硒元素的检测方法,并对富硒食品的前景进行了展望。     

灵芝富硒研究进展

对灵芝的富硒和耐硒特性,硒对灵芝生长代谢的影响,富硒灵芝中硒的赋存形态和含量分布以及富硒灵芝药理活性等方面的研究进展作了概述,并对灵芝富硒研究的发展趋势和前景进行了探讨。     

The paradox of enrichment in an adaptive world

Paradoxically, enrichment can destabilize a predator-prey food web. While adaptive dynamics can greatly influence the stability of interaction systems, few theoretical studies have examined the effect of the adaptive dynamics of interaction-related traits on the possibility of resolution of the paradox of enrichment. We consider the evolution of attack and defence traits of a predator and two prey species in a one predator-two prey system in which the predator practises optimal diet use. The results showed that optimal foraging alone cannot eliminate a pattern of destabilization with enrichment, but trait evolution of the predator or prey can change the pattern to one of stabilization, implying a possible resolution of the paradox of enrichment. Furthermore, trait evolution in all species can broaden the parameter range of stabilization. Importantly, rapid evolution can stabilize this system, but weaken its stability in the face of enrichment.     

The stability of ecosystems: A brief overview of the paradox of enrichment

In theory, enrichment of resource in a predator-prey model leads to destabilization of the system,thereby collapsing the trophic interaction,a phenomenon referred to as "the paradox of enrichment". After it was first pro posed by Rosenzweig (1971), a number of subsequent studies were carried out on this dilemma over many decades. In this article, we review these theoretical and experimental works and give a brief overview of the proposed solutions to the paradox. The mechanisms that have been discussed are modifications of simple predator -prey models in the presence of prey that is inedible, invulnerable, unpalatable and toxic. Another class of mechanisms includes an incorporation of a ratio-dependent functional form,inducible defence of prey and density-dependent mortality of the predator. Moreover, we find a third set of explanations based on complex population dynamics including chaos in space and time. We conclude that,although any one of the various mechanisms proposed so far might potentially prevent destabilization of the predator-prey dynamics following enrichment, in nature different mechanisms may combine to cause stability, even when a system is enriched. The exact mechanisms,which may differ among systems,need to be disentangled through extensive field studies and laboratory experiments coupled with realistic theoretical models.     

Imperfect optimal foraging and the paradox of enrichment

We show that the paradox of enrichment can be theoretically resolved in a flexible predator–prey system in which the predator practices imperfect optimal foraging. A previous study showed that perfect optimal foraging can mitigate increases in the amplitude of population oscillations associated with enrichment, but it did not show a stabilization pattern. Our results show that imperfect optimal foraging can stabilize the system and resolve the paradox of enrichment under nonequilibrium dynamics. Furthermore, the degree of stabilization with enrichment was stronger when the imperfection of optimal foraging was larger.     

Dispersal delays, predator-prey stability, and the paradox of enrichment

It takes time for individuals to move from place to place. This travel time can be incorporated into metapopulation models via a delay in the interpatch migration term. Such a term has been shown to stabilize the positive equilibrium of the classical Lotka-Volterra predator-prey system with one species (either the predator or the prey) dispersing. We study a more realistic, Rosenzweig-MacArthur, model that includes a carrying capacity for the prey, and saturating functional response for the predator. We show that dispersal delays can stabilize the predator-prey equilibrium point despite the presence of a Type II functional response that is known to be destabilizing. We also show that dispersal delays reduce the amplitude of oscillations when the equilibrium is unstable, and therefore may help resolve the paradox of enrichment.     

PCR enrichment techniques to identify the diet of predators

The increasing sensitivity of PCR has meant that in the last two decades PCR has emerged as a major tool in diet studies, enabling us to refine our understanding of trophic links and to elucidate the diets of predators whose prey is as yet uncharacterized. The achievements and methods of PCR-based diet studies have been reviewed several times, but here we review an important development in the field: the use of PCR enrichment techniques to promote the amplification of prey DNA over that of the predator. We first discuss the success of using group-specific primers either in parallel single reactions or in multiplex reactions. We then concentrate on the more recent use of PCR enrichment techniques such as restriction enzyme digests, peptide nucleic acid clamping, DNA blocking and laser capture microdissection. We also survey the vast literature on enrichment techniques in clinical biology, to ascertain the pitfalls of enrichment techniques and what refinements have yielded some highly sensitive methods. We find that while there are several new approaches to enrichment, peptide nucleic acid clamping and DNA blocking are generally sufficient techniques for the characterization of diets of predators and highlight the most important considerations of the approach.     

The dynamics of food chains under climate change and nutrient enrichment

Warming has profound effects on biological rates such as metabolism, growth, feeding and death of organisms, eventually affecting their ability to survive. Using a nonlinear bioenergetic population-dynamic model that accounts for temperature and body-mass dependencies of biological rates, we analysed the individual and interactive effects of increasing temperature and nutrient enrichment on the dynamics of a three-species food chain. At low temperatures, warming counteracts the destabilizing effects of enrichment by both bottom-up (via the carrying capacity) and top-down (via biological rates) mechanisms. Together with increasing consumer body masses, warming increases the system tolerance to fertilization. Simultaneously, warming increases the risk of starvation for large species in low-fertility systems. This effect can be counteracted by increased fertilization. In combination, therefore, two main drivers of global change and biodiversity loss can have positive and negative effects on food chain stability. Our model incorporates the most recent empirical data and may thus be used as the basis for more complex forecasting models incorporating food-web structure.     

Enrichment in a stoichiometric model of two producers and one consumer

We consider a stoichiometric population model of two producers and one consumer. Stoichiometry can be thought of as the tracking of food quality in addition to food quantity. Our model assumes a reduced rate of conversion of biomass from producer to consumer when food quality is low. The model is open for carbon but closed for nutrient. The introduction of the second producer, which competes with the first, leads to new equilibria, new limit cycles, and new bifurcations. The focus of this paper is on the bifurcations which are the result of enrichment. The primary parameters we vary are the growth rates of both producers. Secondary variable parameters are the total nutrients in the system, and the producer nutrient uptake rates. The possible equilibria are: no-life, one-producer, coexistence of both producers, the consumer coexisting with either producer, and the consumer coexisting with both producers. We observe limit cycles in the latter three coexistence combinations. Bifurcation diagrams along with corresponding representative time series summarize the behaviours observed for this model.     

Towards resolving the paradox of enrichment: the impact of zooplankton vertical migrations on plankton systems stability

Eutrophication, often resulting from human activity, is a serious threat to aquatic communities. Theoretical analysis of this phenomenon, based on conceptual mathematical models, leads to controversial predictions known as Rosenzweig's paradox of enrichment. At the same time, field observations demonstrate that real plankton communities exhibit various mechanisms of self-regulation which can buffer negative effects of enrichment. In this paper, we study potential effects of zooplankton vertical migration on stability of plankton systems functioning. We consider an intrinsically unstable plankton model, which is characterized by an unlimited phytoplankton multiplication and population oscillations of increasing amplitude, and investigate whether vertical migrations of zooplankton can stabilize such a system at low plankton densities. By means of developing two different models accounting for different ecological situations, e.g. deep waters and shallow waters, we show that vertical migrations of zooplankton can result in stabilization of eutrophic plankton systems. Thus, we show that this mechanism, rarely taken into account in models of plankton dynamics, may be important for resolving the paradox of enrichment in plankton communities.     

The responses of unstable food chains to enrichment

Summary This article investigates the mean abundances of trophic levels in simple models of two- and three-level food chains as a function of the rate of input of nutrients. The analysis concentrates on cases in which the equilibrium point with all species present is unstable. In most of the models, the instability arises because the consumer species become satiated when food density is high. In unstable two-level systems, bottom level abundance generally increases with increased nutrient input. The abundance of the second level may decrease with increased input. Changes in the intrinsic rate of increase and carrying capacity of the bottom level can have qualitatively opposite effects on trophic level abundances. Refuges for or immigration of the bottom level usually cause both levels to increase in mean abundance with an increased carrying capacity. A variety of different predator—prey models are discussed briefly and the results suggest that increased nutrient input will often increase the abundance of both levels; however, several circumstances can cause the top level to decrease. In three-level systems, an increased carrying capacity can cause extinction of the top level. Extinction may or may not be conditional on the initial densities of the three levels. These results may help explain the observed lack of correlation between productivity and the number of trophic levels in natural food webs, as well as the lack of very long food chains. The results suggest that patterns of abundances across productivity gradients cannot be used to assess the importance of top-down vs bottom-up effects.