The role of periodic boundary forcing in plankton pattern formation

We consider one and two-dimensional minimal models in plankton dynamics. The influence of oscillating boundary forcing functions as agents for triggering pattern formation is discussed. In particular it is found that in these conditions population waves arise for one dimensional models, while for two dimensional models, different amplitudes and frequencies in the boundary forcing generate definite patterns, mimicking the boundary term. This happens even though the model we investigate is very simple. The emergence of these features is an interesting metaphor for the fundamental biological problem of how pattern formation processes may be inevitable in natural heterogeneous ecosystems.     

木根麦冬的种群数量动态

运用静态生命表、生殖力表和Leslie矩阵模型,研究了木根麦冬种群数量动态过程,揭示了种群各龄级植株的动态规律,结果表明,木根麦冬种群为衰退型种群,种群的净增殖率、内禀增长率和周限增长率较低,种群世代周期偏长,种群不能自我更新,在20a内种群幼苗数量和总数量将持续快速下降,木根麦冬种群在16-20a年龄段受到了环境筛的强烈过滤作用。     

皖南丘陵地区小流域氮素径流输出的动态变化

以亚热带北部皖南丘陵地区小流域定位实地观测为基础 ,研究了农林共存小流域氮素径流输出规律。发现小流域氮素径流输出季节性变化明显。降雨和施肥是影响这一变化的重要因子 ,模拟分析表明 ,它们与氮素输出之间具有很好的线性相关关系     

Small mammals as indicators of short-term and long-term disturbance in mixed prairie

Disturbance by military maneuvers over short and long time scales may have differential effects on grassland communities. We assessed small mammals as indicators of disturbance by military maneuvers in a mixed prairie in southern Oklahoma USA. We examined sites on two soil series, Foard and Lawton, across a gradient of disturbance intensity. A MANOVA showed that abundance of small mammals was associated (p = 0.03) with short-term (cover of vehicle tracks) disturbance but was not associated (p = 0.12) with long-term (loss of soil organic carbon, SOC) disturbance intensity. At the individual species level, Sigmodon hispidus (cotton rat) and Peromyscus maniculatus (deer mouse) occurred across all levels of disturbance and in both soil types. Only P. maniculatus abundance changed (p < 0.01) with short-term disturbance and increased by about one individual per 5% of additional track-cover. Abundance of P. maniculatus also increased (p = 0.04) by about three individuals per 1% increase in soil carbon. Chaetodipus hispidus (hispid pocket mouse) and Reithrodontomys fulvescens (fulvous harvest mouse) only occurred in single soil types limiting their potential as more general indicators. Abundance of P. maniculatus was positively related to shifts in plant species composition and likely reflected changes in vegetation structure (i.e. litter depth) and forage availability resulting from disturbance. Peromyscus maniculatus may be a useful biological indicator of ecosystem change because it responded predictably to both long-term and short-term disturbance and, when coupled with soil, plant, and disturbance history variables, can reveal land condition trends.     

Influence of Building Density and Roof Shape on the Wind and Dispersion Characteristics in an Urban Area: A Numerical Study

The Computational Fluid Dynamics code CFX-TASCflow is used for simulating the wind flow and pollutant concentration patterns in two-dimensional wind-tunnel models of an urban area. Several two-dimensional multiple street canyon configurations are studied corresponding to different areal densities and roof shapes. A line source of a tracer gas is placed at the bottom of one street canyon for modelling street-level traffic emissions. The flow fields resulting from the simulations correspond to the patterns observed in street canyons. In particular and in good agreement with observations, a dual vortex system is predicted for a deep flat-roof street canyon configuration, while an even more complex vortex system is evidenced in the case of slanted-roof square street canyons. In agreement with measurement data, high pollutant concentration levels are predicted either on the leeward or the windward side of the street canyon, depending on the geometrical details of the surrounding buildings.     

Testing hypotheses on shape and distribution of ecological response curves

Niche theory with hypotheses on shape and distribution of ecological response curves is used in the studies of resource sharing of competing plant species. Predictions based on theory should be applicable when, e.g., effects of competing species on the ecological tolerances are assessed or species’ diversity along a resource gradient is evaluated. We studied the ecological response curves of competing plant species along a resource gradient in boreal forests. The study was based on nation-wide soil and vegetation data collected from 455 sample plots on boreal forests in Finland. Species response curves along a soil fertility gradient (in terms of C/N ratio) were estimated using generalized additive models. Distribution of species optima and the relationship of niche width and skewness to the location of the optimum were analyzed with new bootstrap tests. The developed tests can account for the effects of truncation observed in the response curves of several species and for the uneven distribution of observations on the gradient.The estimated response curves of the major field layer species of boreal forests were not evenly distributed along soil C/N gradient. The density of optima peaked with relatively high nitrogen availability. Species with optima at low nitrogen availability had relatively broad realized niches. Niche width was negatively correlated with the density of optima. Species optima were packed and niches were narrow at high resource levels. This result suggests that a greater number of more specialized species can occur and interspecific competition decreases niche widths at high resource levels. Species were packed in the gradient where the C/N ratio was lower than 25, i.e., in conditions where nitrification can take place. This indicates that the majority of the vascular plants of boreal forests are favoured by the availability of NO₃⁻. Those few species thriving at high C/N ratios have broader realized niches.     

Critical review of Integrated Water Resources Management: Moving beyond polarised discourse

Integrated Water Resource Management (IWRM) emerged as a popular concept in the water sector in the 20th century. From a highly techno-centric approach in the past, it has taken a new turn embracing Habermasian communicative rationality as a place-based nexus for multiple actors to consensually and communicatively integrate decisions in a hydrological unit. The 'how to integrate' approach had remarkable appeal worldwide in promoting authentic participation of all stakeholders. However, critics argue that the domain of water resource management is a political process of contestation and negotiation; the emphasis is on complexities, contextuality, power dynamics and the importance of analysing real world situations. They demonstrate 'how integration cannot be achieved' given the power dynamics in social interactions. These apparently contradictory discourses draw on different theoretical paradigms and polarise the discourse on IWRM, without offering constructive alternatives. To this end, this paper offers an option to complement this polarised discourse by examining 'how integration actually does take place' in a strategic context thereby facilitating consensual decisions to integrate water management for a sustainable future.     

绵竹县社会经济发展战略的系统动力学研究

摆脱传统思维方式的束缚,采用科学的、系统的、程序化的方法制定我国县级经济和社会发展战略,是我国现代化建设提出的一项艰巨任务。本文旨在通过介绍“绵竹县经济社会发展总体规划(系统工程应用)研究”的核心部分——绵竹县社会经济系统动态仿真模型设计与发展战略的仿真实验择优,阐述系统工程的原理和运用数学模型方法对县级社会经济系统进行总体设计、预演和优化的一点体会。     

CHEMISTRY RESPONSE OF TWO FORESTED WATERSHEDS TO ACID ATMOSPHERIC DEPOSITION1

ABSTRACT: The deposition and chemistry of precipitation were estimated for one year in two forest ecosystems in the South-Central United States. Precipitation, throughfall, litter leachate, and soil leachate were analyzed for a small catchment of pine-hardwoods in southeastern Oklahoma and for a catchment of loblolly pines (Pinus taeda L.) in northern Mississippi. In the pine-hardwood forest, 98 percent of the acid deposition was neutralized, 50 percent in the forest canopy, and 48 percent in the forest floor. In the pine forest, 75 percent of the acid deposition was neutralized, all in the forest floor. The pine-hardwood ecosystem accumulated sulfate, nitrate, and ammonia ions, and lost base cations. During seasons of deficient precipitation, dry deposition appeared to enrich the concentrations of hydrogen, nitrate, sulfate, and ammonia ions in throughfall samples at both locations.