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81.
J. Bastow Wilson Mick J. Crawley Mike E. Dodd Jonathan Silvertown 《Plant Ecology》1996,124(2):183-190
Repeated patterns, of a type that would be expected to result from limitations to species coexistence (i.e. assembly rules) were sought in the Park Grass experiment. This classical grassland experiment was sampled in two years, using replicated biomass samples. Variance in a number of measures was examined, and compared to the variance expected under appropriate null models, the latter based on assumptions of no interactions between species. In each case, an assembly rule would result in low variance. Examining variance in species richness between quadrats within a treatment, there was no indication of constraint on species co-occurrences; variance in richness was actually greater than expected under the null model, attributable to environmental variation or perhaps positive interactions between species. However, there was control on biomass, evidenced by variance in total biomass (i.e. over all species) within a treatment being significantly lower than expected under the null model. There was no indication of community structure based on guilds (i.e. functional types). Although there was in 1991 some, non-significant, indication of a constant proportion of species from the legume guild, there was no sign of such an effect in 1992. Searches for intrinsic guilds failed to converge. There was no indication at all of constancy in the proportional representation of guilds by biomass. Thus, there is good evidence for competitive control on plant growth, but none for control of species occurrences. There is no convincing evidence for guild structure in this community at the scale sampled. Possible conflict is discussed between the existence of evidence for temporal stability but the absence of evidence for spatial uniformity. It is concluded that most of the mechanisms proposed for temporal stability will not necessarily lead to control on spatial variation. For many mechanisms, this would depend on the spatial scale examined. 相似文献
82.
Ectopic ion channels developed locally at the injury site after nerve damage by light ligation around common sciatic nerve of the rats. Different channel types have different processes of formation, accumulation and degeneration. During the first three days after injury, mechanically activated channels that are modulated by Ca++ channel activities first appeared. As the nerve fibers begin to be excited by TEA, a blocker of K+ channels, suggesting that the accumulation of K+ channels, the responsibility of mechanically activated channels was declining. Onset of K+ channels was from the 3rd postoperative day and lasted up to the fiftieth day. This time course of K+ channel development was closely related to allodynia and hyperalgesia of neuropathic animal behaviour. The results suggest that chronic contraction injury induces a dynamic change in the ectopic mechanically activated channels and K+ channels at the injury site of nerve and there is an interchange in the development time courses of the mechanic 相似文献
83.
升流厌氧污泥层反应器动力学模型 总被引:1,自引:0,他引:1
用碘离子作示踪剂,采用矩形脉冲示踪法测定升流厌氧污泥层(UASB)反应器的流动分布。建立了申级返混加沟流模型。模型简单,能够反映反应器流动分布,具有较强的拟合能力和良好的适用性。运用流动模型和Monod方程,建立了UASB反应器稳态模型,并对模型参数进行了估计。通过灵敏度分析,进水基质浓度S。,废水流量Q,最大比基质降解速率,μmax 对出水基质浓度有较大影响。在稳态模型的基础上又建立了UASB反应器动态模态,利用此模型,对出水基质浓度序列Se,和产气量序列Qg进行计算预测,平均偏差分别5.40%和7.46%,标准偏差分别为7.02%和9.66%。 相似文献
84.
动态神经网络中的同步振荡 总被引:3,自引:0,他引:3
目前有一种假设认为同一视觉对象是由一群神经元的同步振荡活动来表征的。这一神经元发放活动的时间特性,是解决视觉信息处理中“结合问题(Bindingproblem)”的可能机制。本文用我们所提出的一种简化现实性神经网络模型[1]所构造的时滞非线性振子网络[2],模拟生物神经网络的同步振荡活动。并考虑了振子各参数的设置与振荡活动的关系,以及网络振子间耦联对同步活动的影响. 相似文献
85.
日粮水平对鲇鱼日总代谢,特殊动力作用和活动代谢的影响 总被引:4,自引:0,他引:4
在25℃不同日粮水平(饥饿─4%体重/d)条件下,采用封闭式呼吸仪测定了31尾鲇鱼(体重72.9─133.3g)的日总代谢率,然后,将鱼限制在呼吸室中的限动笼内测定了其中20尾鲇鱼的静止日总代谢率,并计算出了鲇鱼的特殊动力作用(SDA)和活动代谢率。日总代谢率和活动代谢率都随日粮水平的升高呈“V”形变化,分别在约1%和2%体重/d的日粮水平时最低,SDA的能量支出占摄入能量的22.14%。 相似文献
86.
87.
We assessed the potential for several acoustic properties ofthe advertisement calls of male gray tree frogs to affect relativemating success by relating patterns of variation in these propertiesto minimum differences required to elicit female choice. Dynamicproperties (pulse number, PN; call rate, CR; and duty cycle,DC, the ratio of call duration to call period) varied much morewithin bouts of calling than a static property (dominant frequency,DF) but nevertheless exhibited significant between male variationin three of four breeding seasons. Many multiply recorded malesconsistently produced calls with values substantially aboveor below mean values of males recorded on the same nights. Nightlyranges of variation in PN and CR were often greater than theminimum differences required to elicit female preferences inthe laboratory. In most experiments, females chose high-PN orfast-CR calls over low-PN or slow-CR alternatives, respectively,even if the preferred stimuli were farther away or 6-10 dB lowerin sound pressure level (SPL), provided that differences inPN or CR were 100%. Consistent with these results, females didnot always choose the closer of two calling males in the field.Nightly ranges of variation in DF rarely equaled the minimumdifference required to elicit SPL independent preferences. Femalespreferred a stimulus of high-PN and slow-CR over an alternativeof low-PN or fast-CR with the same acoustic on-time; in twoexperiments, females chose calls of high-PN over low-PN alternativeseven though the playback of the high-PN call was interruptedand the low-PN call was broadcast continuously. Thus, femalepreferences were not merely based on the total time of acousticstimulation. Responses of females tested twice in the same experimentsuggest that phenotypic variation in preference was limitedin our study populations. 相似文献
88.
89.
本研究初步开发了一个用于毛乌素沙地草地种植管理咨询的专家系统ASSG。这个系统将当地生态系统管理专家们的经验知识和对土壤水分动态的理论研究成果结合起来以产生对于土地利用和种植的作物种类及品种的最优管理策略和最适的植被覆盖率。本系统利用3个层次的推理过程和结构化的知识库,通过咨询过程—步步地引导用户得到最优种植管理策略。在每—层次的推理中,本系统提供给用户多重选择,根据用户的意愿进行下一步的推理。这一推理的交互作用机制为用户获得适宜的咨询结果提供了最大的便利性。本系统的主体部分山Turbo Prolog语言完成,该语言是一种用于开发专家系统的描述性语言。基于土壤水分平衡原理的最优植被覆盖率模型由C语言实现,并应用多语言编程技术将之嵌入程序主体中。系统的样本运行结果表明本系统运行便利,并能产生合理的种植管理策略。 相似文献
90.
We investigated how the population dynamics of the same bird species varied in different environments, and how the population dynamics of different species varied in the same environment, by calculating long-term population trends for 59 insectivorous songbird species in 22 regions or strata of eastern and central North America using data from the North American Breeding Bird Survey. Of the 47 species that occurred in more than one region 77% increased in some regions and declined in others. Of the 22 regions 91% had some species that increased and others that decreased. There were only slightly more significant correlations between strata in species trends and between species for stratum trends than would be expected by chance. Because of nonlinearities in the data, the actual patterns of population fluctuations of the same species in different regions and of different species in the same region were even more heterogeneous than suggested by our analyses of linear trends. We conclude that these bird species respond to spatial and temporal variation in their environment in a very individualistic fashion. These individualistic responses show that the extrapolation of population trends gained from a few local studies to a larger spatial scale, and the use of a few indicator species to monitor the status of a broader community, are suspect. 相似文献