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1.
ABSTRACT. An individual‐based model of stream trout is analyzed by testing its ability to reproduce patterns of population‐level behavior observed in real trout: (1) “self‐thinning,” a negative power relation between weight and abundance; (2) a “critical period” of density‐dependent mortality in young‐of‐the‐year; (3) high and age‐specific inter‐annual variability in abundance; (4) density dependence in growth; and (5) fewer large trout when pool habitat is eliminated. The trout model successfully reproduced these patterns and was useful for evaluating their theoretical basis. The model analyses produced new explanations for some field observations and indicated that some patterns are less general than field studies indicate. The model did not reproduce field‐observed patterns of population variability by age class, discrepancies potentially explained by site differences, predation mortality being more stochastic than the model assumes, or uncertainty in the field study's age estimates.  相似文献   

2.
Abstract In this paper, we describe an individual‐based model of the interaction between a producer and herbivore species. The interaction occurs in a 2‐dimensional matrix of individual cells. The producer organism grows in the cells and the herbivores move between the cells, towards areas of high concentration of producer. Herbivores may die of starvation or they may reproduce asexually. The model is not built to represent a specific existing system but is a parsimonious generalized model of producer–herbivore interaction designed to test spatial effects. Although the model algorithm is kept simple—the herbivores have no learning or social behavior and have a minimal foraging strategy—the model displays some characteristics of real systems such as metapopulation behavior. We find significant effects on the herbivore and producer populations of the maximum move distance per step of the herbivores, the shape of the two‐dimensional matrix, the quality of a corridor between patches habitable by the herbivores, and edge effects with fuzzy edges. The behavior of the model is comparable with empirical observations found in the literature, and we suggest that this simple model may be used to investigate the mechanism of these real effects.  相似文献   

3.
The Gierer-Meinhardt's Model with a time delaydx(t)/dt=Co-bx(t)+cx2(t-τ)/y(t)(1+kx2(t-τ)),dy(t)/dt=x2(t)-ay(t).is studied. It is proved that there exists a Hopf bifurcation. Some conditions are established under which the equilibrium is globally stable.  相似文献   

4.
ABSTRACT. In this paper we report the use of an individual‐based model of predator‐prey interaction to explore the effects of “within generational” and ‘between generational’ updating of a system level variable. We also report the importance of diversity within the simulated populations. Our findings support those of Grimm and Uchmánski [1994] in regard to the importance of the timing of system level variables, and support Grimm and Uchmañski and others in regard to the importance of the level of diversity across the population. The significance of these findings is emphasized by the fundamental differences between our model and that of Grimm and Uchmánski in regard to the assumptions made about resource flow in the system. This paper was presented at the 2004 Research Modeling Association World Conference on Natural Resource Modeling in Melbourne, Australia.  相似文献   

5.
1 IntroductionConsider the fOllowing Logistic modelwhere A denotes the forward difference operator defined by Ax. = xu l -- x.,{r.}7=, is a sequence of nonnegative real number, {k.}7=, is a sequence ofnonnegative integers, which satisfies jt(n -- k.) = co) }it sup k. = co? andK is a positive constant. Obviously, K is the unique positive equilibrium pointof Eq.(1).FOr the special cases of Eq.(l)f re = r > 0 or k. == k 6 {0, 1, 2,' .}, therehave been many papers studying them. See, for exa…  相似文献   

6.
GLOBALATTRACTIVITYINADISCRETEMODELOF NICHOLSON'S BLOWFLIESLiJingwen(李经文)(ShaoyangTeachersCollege湖南邵阳师专,邮编;422000)Abstract:Cons...  相似文献   

7.
In this paper, we establish new sufficient conditions for the infected equilibrium of a nonresident computer virus model to be globally asymptotically stable. Our results extend two kind of known results in recent literature.  相似文献   

8.
在本文中,我们进一步研究时滞微分方程它由Mackey和Ladas[2]提出作为血生成模型.我们建立了(*)的平衡是全局吸引子的新的充分条件,我们还改进了Gopalsamy,Kulenovic和Ladas[1]所得到的某些结果.  相似文献   

9.
In this paper, we present a competition modei of e-commerce sites with the property of "better for better". Then we qualitatively analyze the special case of two dimensions. So we prove that there does not exist limit cycle, in the first quadrant of the phase plane and all trajectories tend to some singular points.  相似文献   

10.
1IlltroductionInl99o,MiltinandB.lairl1]raisedadifferenceequationasapopulationmodelforthegrowthofthebobwhitequailpopulationofnorthernWisconsin.Inl994,Ladas,G.proposedthefollowingopenproblem[']:"(a)Investigatetheboundedness,persistence,permanence,oscillation,periodicity,andglobalattractivity;(b)ExtendEq.(*)byintroducingdelaysintothemodel,andinvestigatethedelayedequation.".Inl996,TangHeng-shengandOuChun-hua[3]considereditsglobalattrac-tivity,partlyansweredaboveopenproblem(a).Inl999,byintrodu…  相似文献   

11.
赵汇涛 《数学杂志》2016,36(1):191-198
本文研究了一类比率依赖的捕食者-食饵模型的Hopf分支问题,运用吴建宏等人利用等变拓扑度理论建立起的一般泛函微分方程的全局分支理论,得到了由系统的正平衡点分支出来的周期解的全局存在性,最后利用数值模拟验证了理论分析的正确性.  相似文献   

12.
In this paper, we study a predator-prey model with prey refuge and disease. We study the local asymptotic stability of the equilibriums of the system. Further, we show that the equilibria are globally asymptotically stable if the equilibria are locally asymptotically stable. Some examples are presented to verify our main results. Finally, we give a brief discussion.  相似文献   

13.
土地资源的可拓性及优化配置系统结构模型   总被引:8,自引:0,他引:8  
本文应用可拓学的理论和方法,对土地资源的特征及优化配置原理进行分析,设计了优化配置系统结构模型,为土地资源的优化配置和合理利用提供了一种新的科学方法。  相似文献   

14.
全球变暖的宏观经济增长模型   总被引:1,自引:0,他引:1  
本文研究了全球变暖的减排对策及其对经济环境的影响.运用动态最优化的方法,对该系统进行静态与动态的分析,并且讨论了参数对经济环境的影响.对我国制定全球变暖的对策有一定启发意义.  相似文献   

15.
This paper investigates the global stability of a viral infection model with lytic immune response. If the basic reproductive ratio of the virus is less than or equal to one, by the LaSalle's invariance principle, the disease-free steady state is globally asymptotically stable. If the basic reproductive ratio of the virus is greater than one but less than or equal to a constant, which is defined by the parameters of the model, then the immune-exhausted steady state is globally asymptotically stable. The endemic steady state is globally asymptotically stable if the inverse is valid.  相似文献   

16.
The existence of a positive periodic solution foru'(t) =u(t)[α(t)-1+β(t)/1+uk(t-τ(t))], t≥0is established. Some sufficient conditions are obtained for the periodic solution to be globally attractive.  相似文献   

17.
马文君  孙亮亮 《数学杂志》2017,37(4):731-736
本文研究一类带食饵趋向的Beddington-DeAngelis捕食者-食饵扩散模型,其中食饵趋向性描述的是捕食者对食饵数量变化而产生的一种正向迁移.利用Neumann热半群的Lp-Lq估计和带抛物型方程Moser迭代的Lp估计,获得了该模型经典解的整体有界性.  相似文献   

18.
ABSTRACT. The excessive and unsustainable exploitation of our marine resources has led to the promotion of marine reserves as a fisheries management tool. Marine reserves, areas in which fishing is restricted or prohibited, can offer opportunities for the recovery of exploited stock and fishery enhancement. In this paper we examine the contribution of fully protected tropical marine reserves to fishery enhancement by modeling marine reserve‐fishery linkages. The consequences of reserve establishment on the long‐run equilibrium fish biomass and fishery catch levels are evaluated. In contrast to earlier models this study highlights the roles of both adult (and juvenile) fish migration and larval dispersal between the reserve and fishing grounds by employing a spawner‐recruit model. Uniform larval dispersal, uniform larval retention and complete larval retention combined with zero, moderate and high fish migration scenarios are analyzed in turn. The numerical simulations are based on Mombasa Marine National Park, Kenya, a fully protected coral reef marine reserve comprising approximately 30% of former fishing grounds. Simulation results suggest that the establishment of a fully protected marine reserve will always lead to an increase in total fish biomass. If the fishery is moderately to heavily exploited, total fishery catch will be greater with the reserve in all scenarios of fish and larval movement. If the fishery faces low levels of exploitation, catches can be optimized without a reserve but with controlled fishing effort. With high fish migration from the reserve, catches are optimized with the reserve. The optimal area of the marine reserve depends on the exploitation rate in the neighboring fishing grounds. For example, if exploitation is maintained at 40%, the ‘optimal’ reserve size would be 10%. If the rate increases to 50%, then the reserve needs to be 30% of the management area in order to maximize catches. However, even in lower exploitation fisheries (below 40%), a small reserve (up to 20%) provides significantly higher gains in fish biomass than losses in catch. Marine reserves are a valuable fisheries management tool. To achieve maximum fishery benefits they should be complemented by fishing effort controls.  相似文献   

19.
GLOBAL STABILITY OF AN SIRS EPIDEMIC MODEL WITH DELAYS   总被引:2,自引:0,他引:2  
In this article, an SIRS epidemic model spread by vectors (mosquitoes) which have an incubation time to become infectious is formulated. It is shown that a disease-free equilibrium point is globally stable if no endemic equilibrium point exists. Further, the endemic equilibrium point (if it exists) is globally stable with a respect "weak delay". Some known results are generalized.  相似文献   

20.
In this paper, an SIR epidemic model with vaccination for both the newborns and susceptibles is investigated, where it is assumed that the vaccinated individuals have the temporary immunity. The basic reproduction number determining the extinction or persistence of the infection is found. By constructing a Lyapunov function, it is proved that the disease free equilibrium is globally stable when the basic reproduction number is less than or equal to one, and that the endemic equilibrium is globally stable wh...  相似文献   

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