利用牧草生长-消费模型优化草场放牧方案

从理论上探讨了草场生态系统牧草的生长过程和消费过程,采用数学模型方法模拟了两者的动态变化规律,分析了两者在草场生态系统生态平衡中的作用机制．运用牧草的生长和消费模型模拟特定生产周期内草场生态系统的累积牧草消费量,提出优化的草场放牧方案。为实际生产提供参考依据．     

Stable adaptive algorithm for simultaneous estimation of time-varying parameters and state variables in aerobic bioprocesses

The application of modern model based control algorithms in the bioprocesses is hampered by the lack of accurate and cheap on-line sensors, capable of providing on-line measurements of the main process variables and parameters. In this paper, a new approach for estimation of immeasurable time-varying parameters and state variable is presented for a class of aerobic bioprocesses using only on-line measurements of the oxygen uptake rate. The approach consists in the design of a new parameter estimator of biomass growth rate and yield coefficient for oxygen consumption on the basis of the theory of adaptive estimation. The dynamical equation of the measurable reaction rate, oxygen uptake rate, is presented as a linear one with respect to the biomass growth rate and the yield coefficient for oxygen consumption. In this way, the structure of the proposed estimator becomes linear time-varying one. After some mathematical transformations, that structure is presented in a form, allowing to be derived the stability conditions using some theoretical results concerning the stability of adaptive observers. The estimates of the yield coefficient for oxygen consumption, the biomass concentration and specific growth rate are obtained then on the basis of the generated estimates using well known kinetic models of bioprocesses. With respect to previous similar approaches, the new estimation algorithm gives stable estimates not only of immeasurable state variable and reaction rates but likewise of an yield coefficient. The behavior of the proposed estimator is studied under inexact initial conditions, step changes of dilution rate and in the presence of measurement noise by simulations using a process model, which belongs to the investigated class of bioprocesses.     

Growth energetics of an alkaline serine protease-producing strain of Bacillus clausii during continuous cultivation

Glucose-limited chemostats were used to determine the growth yields of biomass of Bacillus clausii PP 473-8 producing an alkaline serine protease Savinase (Novozymes A/S, Bagsværd, Denmark) and a low yield of biomass on oxygen was observed. The energy metabolism was investigated further by setting up simple stoichiometric models for growth on glucose and citrate. In order to determine the parameters in the models, a macromolecular biomass composition was determined based on measured values of protein and RNA combined with literature data. From the macromolecular composition of the biomass the theoretical co-factor and building block requirements needed for biomass formation were calculated. Using the stoichiometric models and data for growth on glucose and citrate the amount of ATP needed for biomass synthesis was estimated to 42.0 mmol ATP/gDW, the P/O ratio to 0.68 and the ATP maintenance to 2.93 mmol ATP/gDW/h. From these values it is concluded that the high oxygen consumption compared with other Bacillus species is due to a low efficiency in respiration resulting in a low P/O ratio. Finally, the energetic parameters were estimated for different architectures of the respiratory chain.     

Metaphysiological and evolutionary dynamics of populations exploiting constant and interactive resources:R—K selection revisited

Summary I begin by reviewing the derivation of continuous logistic growth and dynamic consumer—resource interaction equations in terms of specific resource extraction and biomass conversion functions that are considered to hold at a population level. Evolutionary stable strategy (ESS) methods are discussed for analysing populations modelled by these equations. The question of selection trade-offs is then considered, particularly in the context of populations being efficient at extracting resources versus converting resources to their own biomass. Questions relating to single populations with high versus low conversion rates and interacting populations with high versus low self-interference rates are also considered. The models discussed here demonstrate conclusively that self-interference is an essential part of any consumption process: without it population growth and interaction processes do not make any sense. The analysis clarifies concepts relating to the somewhat discredited notion ofr—K selection.     

Division synchrony and the dynamics of microbial populations: A size-specific model

A discrete, environmentally coupled, size-specific model of microbial population dynamics in continuous culture is presented. It is mathematically simpler than other models based on similar assumptions and lends itself to numerical and analytic solutions. It displays several phenomena which have been reported in the experimental literature but which are not well understood; specifically, a loose relationship between biomass and numbers (i.e., a time lag between mass growth and cell division) and a critical damping of biomass while numbers continue to oscillate. In addition, the model provides several new predictions: The stable biomass distribution is independent of the environmental factors considered in the model and uniformly distributes the biomass among the size classes. The rate of approach to stability and the frequency of waves through the size distributions are a function of the flow rate and the variance in rate of growth and size at division. The model should provide a useful basis for studying the effects of size specificity on the dynamics of microbial populations cultured in chemostats.     

Demography and dynamics of three wild horse populations in the Australian Alps

Wild horses (Equus caballus) are a non‐native species occupying over 2800 km² of the nationally significant Australian Alps National Parks. We estimated key demographic parameters (fecundity, adult and juvenile survival and annual finite population growth rate) over 3 years and related these to horse body condition and available food for three populations under natural conditions, and found a trend consistent with food limitation. The populations were independent, with different site characteristics and occupied areas, identified by land managers, as areas of concern about possible conservation impacts. Annual fecundity and juvenile survival varied across sites averaging between 0.21 and 0.31 female young per adult female, and 0.83 and 0.90 per annum, respectively, and annual adult survival was consistent across sites averaging 0.91 per annum. One population was increasing (λ = 1.09 year^?1; 95% CI 1.04–1.14) and two populations were stable (λ ～ 1.0 year^?1). Mean body condition of horses was positively correlated with mean pasture biomass rank. Across the three populations, fecundity, recruitment, body condition and annual finite population growth rate were lowest when mean pasture biomass rank was lowest and conversely highest when pasture rank was highest. We conclude that food limitation appears to be operating across these three sites. We used our results to assess the sensitivity of annual finite rate of increase (λ) to changes in key demographic parameters and found that λ was most sensitive to a change in adult survival, with the second most sensitive parameter being fecundity. Thus, if the aim of management is to reduce the size of the wild horse population then targeting adult survival is most important, followed by fecundity. Finally, we estimated the linear, negative, numerical response for wild horses between annual λ and horses per unit pasture biomass.     

Eelgrass, Zostera marina, growth along depth gradients: upper boundaries of the variation as a powerful predictive tool

1200 measurements of eelgrass ( Zostera marina ) biomass, shoot density and cover along 19 depth gradients in Øresund, located between Denmark and Sweden, were analysed to characterise growth of eelgrass in relation to depth. The large data set allowed analyses of boundaries of distribution as well as of average trends. Natural variability is large in shallow water where populations are disturbed by wave action and other physical parameters. Models based on average values, therefore, did not adequately describe growth regulation by resources, and only explained a minor part (up to 30%) of the overall variation in data. In contrast, boundary functions, which describe the upper bounds of distributions, focus on the variation produced by the ultimately growth-regulating resource, and therefore provide models with high predictive power. An exponential model explained up to 90% of the variation in upper bounds of eelgrass shoot density as a function of depth and indicated that shoot density was ultimately regulated by light availability. The boundary functions demonstrated that eelgrass shoot density, biomass and cover followed markedly different patterns as functions of depth and were affected differently by the factors governing their distribution. In addition, boundary functions revealed informative spatial structures in data and illustrated whether a given general trend was caused by changes in maximum values, minimum values or both. For example, upper and lower boundaries of biomass-shoot density relations changed markedly with depth, demonstrating depth-related changes in intraspecific succession and competition patterns. Boundary functions are therefore suggested as a promising tool for analysing ultimate regulating factors of distribution and growth of organisms when large data sets are available.     

How far details are important in ecosystem modelling: the case of multi-limiting nutrients in phytoplankton-zooplankton interactions

We try to answer the question of to what extent details in nutrient uptake and phytoplankton physiology matter for population and community dynamics. To this end, we study how two nutrients interact in limiting phytoplankton growth. A popular formulation uses a product-rule for nutrient uptake, which we compare with that on the basis of synthesizing units. We first fit different nutrient uptake models to a dataset and conclude that the quantitative differences between the models are small. Then we study the sensitivity of phytoplankton growth and zooplankton-phytoplankton interactions (ZPi) models to uptake formulations. Two population models are compared; they are based on different assumptions on the relation between nutrient uptake and phytoplankton growth. We find that the population and community models are sensitive to uptake formulations. According to the uptake formulation used in the ZPi models, qualitative differences can be observed. Indeed, although two models based on functions with similar shapes have close equilibria, these can differ in stability properties. Since stability involves the derivatives of formulas, even if two formulas provide close values, large numerical differences in the stability criterion may occur after derivation. We conclude that mechanistic details can be of importance for community modelling.     

A new method for non-destructive measurement of biomass, growth rates, vertical biomass distribution and dry matter content based on digital image analysis

BACKGROUND AND AIMS: Biomass is an important trait in functional ecology and growth analysis. The typical methods for measuring biomass are destructive. Thus, they do not allow the development of individual plants to be followed and they require many individuals to be cultivated for repeated measurements. Non-destructive methods do not have these limitations. Here, a non-destructive method based on digital image analysis is presented, addressing not only above-ground fresh biomass (FBM) and oven-dried biomass (DBM), but also vertical biomass distribution as well as dry matter content (DMC) and growth rates. METHODS: Scaled digital images of the plants silhouettes were taken for 582 individuals of 27 grass species (Poaceae). Above-ground biomass and DMC were measured using destructive methods. With image analysis software Zeiss KS 300, the projected area and the proportion of greenish pixels were calculated, and generalized linear models (GLMs) were developed with destructively measured parameters as dependent variables and parameters derived from image analysis as independent variables. A bootstrap analysis was performed to assess the number of individuals required for re-calibration of the models. KEY RESULTS: The results of the developed models showed no systematic errors compared with traditionally measured values and explained most of their variance (R(2) > or = 0.85 for all models). The presented models can be directly applied to herbaceous grasses without further calibration. Applying the models to other growth forms might require a re-calibration which can be based on only 10-20 individuals for FBM or DMC and on 40-50 individuals for DBM. CONCLUSIONS: The methods presented are time and cost effective compared with traditional methods, especially if development or growth rates are to be measured repeatedly. Hence, they offer an alternative way of determining biomass, especially as they are non-destructive and address not only FBM and DBM, but also vertical biomass distribution and DMC.     

A model study of stability and oscillations in the myocardial cell membrane

As a step towards an improved understanding of cardiac arrhythmias caused by abnormal automaticity, we perform a stability analysis of a Hodgkin-Huxley model of the myocardial cell membrane (modified Beeler-Reuter, MBR). The bifurcation structure of the model is obtained as a function of three parameters: the intensity of an applied constant current; the potassium equilibrium potential representing the accumulation of K+ ions in the external medium; and the maximum conductance of the slow inward current mimicking the local application of catecholamines on the membrane. For a range of parameter values, the model exhibits either stable automaticity or bistability between two quiescent states or between a quiescent state and an oscillatory state. These transformations of the bifurcation structure are shown to depend on the interrelationship between three elements: the activation of the slow inward current, the region of high slope conductance of the time-independent potassium current functions, and the slow variables controlling the activation of the potassium current and the inactivation of the slow inward current. Reduced two- and three-dimensional models are shown to reproduce the main stability properties of the full MBR model and to facilitate the understanding of its dynamic behavior. The onset of instability and the oscillatory features of the MBR model are in good agreement with relevant experimental results, and possible sources of disagreement on certain points are discussed.     

植株密度和氮素互作对垂穗披碱草生物量分配的影响

垂穗披碱草（Elymus nutans）是高寒地区建植和改良栽培草地的首选草种。虽然合理植株密度和氮素添加量是垂穗披碱草栽培草地稳产的关键因子,但两者之间是否存在最佳互作组合仍不清楚。采用盆栽试验,通过分析不同植株密度（58、102、146株/m²）和氮素添加量（0、200、400 mg/kg）组合状态下垂穗披碱草株高、单株分蘖数、地上生物量、地下生物量、根系体积和地上地下生物量比,以确定理论上是否存在植株密度和氮素添加量的最佳组合。结果表明：随植株密度增加,垂穗披碱草株高、地上生物量和地上地下生物量比值均先增加后降低,而单株分蘖数逐渐减小,根系体积和地下生物量先增加后保持相对稳定;随氮素添加量增加,垂穗披碱草单株分蘖数、地上生物量和地上地下生物量比值均表现为先增加后降低,地下生物量逐渐降低。植株密度与氮素添加量互作虽然对垂穗披碱草的根系体积和单株分蘖数没有显著影响,但两者互作显著影响了垂穗披碱草株高、地上生物量、地下生物量、地上地下生物量比（P<0.01）,这些指标与植株密度和氮素添加量的关系均表现为一个开口向下的抛物面。当植株密度为102株/m²和氮素添加量为200 mg/kg时,垂穗披碱草栽培草地产量最大,生物量分配最优。垂穗披碱草植株密度和氮素添加互作时理论上存在最佳组合,这为垂穗披碱草栽培草地的田间管理提供了理论依据。     

The prey-dependent consumption two-prey one-predator models with stage structure for the predator and impulsive effects

In this paper, we consider the prey-dependent consumption two-prey one-predator models with stage structure for the predator and impulsive effects. By applying the Floquet theory of linear periodic impulsive equation, we show that there exists a globally asymptotically stable pest-eradication periodic solution when the impulsive period is less than some critical value, that is, the pest population can be eradicated totally. But from the point of ecological balance and saving resources, we only need to control the pest population under the economic threshold level instead of eradicating it totally, and thus, we further prove that the system is uniformly permanent if the impulsive period is larger than some critical value, and meanwhile we also give the conditions for the extinction of one of the two preys and permanence of the remaining species. Thus, we can use the stability of the positive periodic solution and its period to control insect pests at acceptably low levels. Considering population communities always are imbedded in periodically varying environments, and the parameters in ecosystem models may oscillate simultaneously with the periodically varying environments, we add a forcing term into the prey population's intrinsic growth rate. The resulting bifurcation diagrams show that with the varying of parameters, the system experiences process of cycles, periodic windows, periodic-doubling cascade, symmetry breaking bifurcation as well as chaos.     

The effects of land use change on native dung beetle diversity and function in Australia's Wet Tropics

The impacts of land use change on biodiversity and ecosystem functions are variable, particularly in fragmented tropical rainforest systems with high diversity. Dung beetles (Scarabaeinae) are an ideal group to investigate the relationship between land use change, diversity and ecosystem function as they are easily surveyed, sensitive to habitat modification and perform many ecosystem functions. Although this relationship has been investigated for dung beetles in some tropical regions, there has been no study assessing how native dung beetles in Australia's tropical rainforests respond to deforestation, and what the corresponding consequences are for dung removal (a key ecosystem function fulfilled by dung beetles). In this study we investigated the relationship between dung beetle community attributes (determined through trapping) and function (using dung removal experiments that allowed different dung beetle functional groups to access the dung) in rainforest and cleared pasture in a tropical landscape in Australia's Wet Tropics. Species richness, abundance and biomass were higher in rainforest compared to adjacent pasture, and species composition between these land use types differed significantly. However, average body size and evenness in body size were higher in pasture than in rainforest. Dung removal was higher in rainforest than in pasture when both functional groups or tunnelers only could access the dung. Increased dung removal in the rainforest was explained by higher biodiversity and dominance of a small number of species with distinct body sizes, as dung removal was best predicted by the evenness in body size of the community. Our findings suggest that functional traits (including body size and dung relocation behaviour) present in a dung beetle community are key drivers of dung removal. Overall, our results show that deforestation has reduced native dung beetle diversity in Australian tropical landscapes, which negatively impacts on the capacity for dung removal by dung beetles in this region.     

Biomass allocation, shade tolerance and seedling survival of the invasive species

Berberis darwinii (Berberidaceae) is a serious environmental weed in New Zealand, capable of invading a range of different light environments from grazed pasture to intact forest. According to optimal partitioning models, some plants optimise growth under different environmental conditions by shifting biomass allocation among tissue types (e.g. roots, shoots) to maximise the capture of limiting resources (e.g. water, light). We examined patterns of growth, biomass allocation, and seedling survival in Berberis darwinii to determine whether any of these factors might be contributing to invasion success. Growth and biomass allocation parameters were measured on seedlings grown for 7 months in five natural light environments in the field. Survival was high in the sunniest sites, and low in the shadiest sites. Seedlings grown in full sun were an order of magnitude taller and heavier, had five times as many leaves, and proportionally more biomass allocated to leaves than seedlings grown in other light environments. In the shade, leaves were bigger and thinner, and leaf area as a proportion of total plant biomass increased, but the proportion of above- to below-ground biomass was similar across all light and soil moisture environments. In summary, although leaf traits were plastic, patterns of biomass allocation did not vary according to optimal partitioning models, and were not correlated with patterns of seedling survival. Implications for the management of this invasive species are discussed.     

Land-use change in a tropical mountain rainforest region of southern Ecuador affects soil microorganisms and nutrient cycling

Over the past decades, the tropical mountain rainforest of southern Ecuador has been threatened by conversion to cattle pastures. Frequently, these pastures are invaded by bracken fern and abandoned when bracken becomes dominant. Changes in land-use (forest–pasture–abandoned pasture) can affect soil microorganisms and their physiological responses with respect to soil carbon and nutrient cycling. In situ investigations on litter decomposition and soil respiration as well as biogeochemical characterization of the soil were carried out to identify the driving factors behind. The conversion of forest to pasture induced a pronounced increase in CO₂–C effluxes to 12.2 Mg ha^?1 a^?1 which did not decrease after abandonment. Soil microbial activity and biomass showed a different pattern with lowest values at forest and abandoned pasture sites. With 3445 mg kg^?1 (0–5 cm) microbial biomass carbon (MBC by CFE-method), the active pasture had a more than three times higher value than forest and abandoned pasture, which was among the highest in tropical pasture soils. A shift in the microbial community structure (phospholipid fatty acid, PLFA) was also induced by the establishment of pasture land; the relative abundance of fungi and Gram-negative bacteria increased. PLFA fingerprints of the forest organic layer were more similar to pasture than to forest mineral soil. Chemical properties (pH value, exchangeable cations) were the main factors influencing the respective microbial structure. Bracken-invasion resulted in a decrease in the quantity and quality of above- and belowground biomass. The lower organic substance and nutrient availability induced a significant decline in microbial biomass and activity. After pasture abandonment, these differences in soil microbial function were not accompanied by pronounced shifts in the community structure and in soil pH as was shown for the conversion to pasture. A disconnection between microbial structure and function was identified. Similar soil CO₂–C effluxes between active and abandoned pasture sites might be explained by an underestimation of the effluxes from the active pasture site. All measurements were carried out between grass tussocks where fine-root density was about 2.6 times lower than below tussocks. Thus, lower proportions of root respiration were expected than below tussocks. Overall, soil microorganisms responded differently to changes in land-use from forest to pasture and from pasture to abandoned pasture resulting in pronounced changes of carbon and nutrient cycling and hence of ecosystem functioning.     

棉花蕾花铃生物量、氮累积特征及临界氮浓度稀释模型

在大田栽培条件下,于河南安阳（黄河流域黄淮棉区）和江苏南京（长江流域下游棉区）设置了棉花氮素水平试验,对不同氮素水平条件下棉花蕾花铃的生物量、氮素累积及氮浓度的动态变化进行分析,并依据Justes的临界氮浓度稀释模型确定方法,研究棉花蕾花铃临界氮浓度稀释模型。结果表明：棉花蕾花铃的生物量增长和氮吸收累积均受氮素水平的影响,其动态变化符合S型曲线,氮累积的快速起始时间较生物量早1～5d;氮浓度过高或过低均不利于产量形成,蕾花铃等器官存在氮奢侈消费现象;氮浓度随施氮量的增加而升高、随生育进程的推移而降低,其生物量累积量与氮浓度间符合幂函数关系,两试点蕾花铃氮稀释曲线模型形式相同,但模型参数a不同,不同生态区存在独立的临界氮稀释曲线模型。由于临界稀释模型具有明确的生物学意义,可以作为定量诊断蕾花铃氮营养动态变化的指标之一。     

Accumulation characteristics of biomass and nitrogen and critical nitrogen concentration dilution model of cotton reproductive organ

Several nitrogen (N) field experiments were carried out in Nanjing and Anyang, China, to study the dynamic characteristics of biomass accumulation and N uptake, and to define the dilution curve for critical N concentration in cotton reproductive organ over the growth period. The results show that the total biomass and N accumulation were affected significantly by the rate of N application, exhibiting a sigmoid curve over time. The beginning time of fast N accumulation was 1–5 d earlier than that of biomass accumulation. The cotton lint yield was correlated with N concentration in the reproductive organ and fluctuated with varying N concentration, indicating the existence of luxurious N consumption in the cotton reproductive organ. The N concentration increased with increasing N application rates, and decreased gradually during the growth period. The relationship between biomass and N concentration can be described with a power equation. The patterns of the N concentration dilution model were consistent at both experimental sites, but the model parameter values of a differed. The results presented in this paper indicate that a critical N concentration dilution curve for cotton reproductive organ is independent of ecological region and can be described with a power equation.