层次分析法在闽南沿海山地混交林优化模式选择上的应用

采用层次分析法(AHP)对闽南沿海山地各混交经营模式进行层次决策选择,从层次选择模型和判断矩阵的构建入手,对评价因子和混交优化模式进行排序并经一致性检验,结果表明,所构建的判断矩阵的随机一致性比率=0.0646<0.10,总排序的=0.0516<0.10,均具有满意的一致性和可靠性,选择出的优化模式与现实生产实际相吻合,说明层次分析法在混交林经营模式的定量化选择上的应用是可行的.     

A complex social structure with fission–fusion properties can emerge from a simple foraging model

Precisely how ecological factors influence animal social structure is far from clear. We explore this question using an agent-based model inspired by the fission–fusion society of spider monkeys (Ateles spp). Our model introduces a realistic, complex foraging environment composed of many resource patches with size varying as an inverse power law frequency distribution with exponent β. Foragers do not interact among them and start from random initial locations. They have either a complete or a partial knowledge of the environment and maximize the ratio between the size of the next visited patch and the distance traveled to it, ignoring previously visited patches. At intermediate values of β, when large patches are neither too scarce nor too abundant, foragers form groups (coincide at the same patch) with a similar size frequency distribution as the spider monkey’s subgroups. Fission–fusion events create a network of associations that contains weak bonds among foragers that meet only rarely and strong bonds among those that repeat associations more frequently than would be expected by chance. The latter form subnetworks with the highest number of bonds and a high clustering coefficient at intermediate values of β. The weak bonds enable the whole social network to percolate. Some of our results are similar to those found in long-term field studies of spider monkeys and other fission–fusion species. We conclude that hypotheses about the ecological causes of fission–fusion and the origin of complex social structures should consider the heterogeneity and complexity of the environment in which social animals live.     

Enchytraeid population dynamics: Resource limitation and size-dependent mortality

Enchytraeids are regarded as keystone soil organisms in forest ecosystems. Their abundance and biomass fluctuate widely. Predicting the consequences of anthropogenic disturbances requires an understanding of the mechanisms underlying enchytraeid population dynamics. Here I develop a simple model, which predicts that the type of dynamics is controlled by resource input rate. If fungal resource input is a discrete event once a year, an exponential growth phase is followed by starvation and sharp decline of enchytraeid abundance. Model simulations with three different forcing functions were compared to field data. Initial parameter values were obtained from various independent sources, and parameters were estimated by minimizing the residual sum of squares. The best fitting model with resource addition once a year explained 39% of the variation in enchytraeid biomass over an 8-year study period. Further, variation in rainfall explained 59% of the variation in R² of the exponential phase models, which is also an index of the stability of population size-structure. The results emphasize the importance of resource limitation for enchytraeid population dynamics and support the hypothesis that the mortality during the decline phase is size-dependent.     

Effects of Harvesting Flowers from Shrubs on the Persistence and Abundance of Wild Shrub Populations at Multiple Spatial Extents

Abstract: Wildflower harvesting is an economically important activity of which the ecological effects are poorly understood. We assessed how harvesting of flowers affects shrub persistence and abundance at multiple spatial extents. To this end, we built a process‐based model to examine the mean persistence and abundance of wild shrubs whose flowers are subject to harvest (serotinous Proteaceae in the South African Cape Floristic Region). First, we conducted a general sensitivity analysis of how harvesting affects persistence and abundance at nested spatial extents. For most spatial extents and combinations of demographic parameters, persistence and abundance of flowering shrubs decreased abruptly once harvesting rate exceeded a certain threshold. At larger extents, metapopulations supported higher harvesting rates before their persistence and abundance decreased, but persistence and abundance also decreased more abruptly due to harvesting than at smaller extents. This threshold rate of harvest varied with species’ dispersal ability, maximum reproductive rate, adult mortality, probability of extirpation or local extinction, strength of Allee effects, and carrying capacity. Moreover, spatial extent interacted with Allee effects and probability of extirpation because both these demographic properties affected the response of local populations to harvesting more strongly than they affected the response of metapopulations. Subsequently, we simulated the effects of harvesting on three Cape Floristic Region Proteaceae species and found that these species reacted differently to harvesting, but their persistence and abundance decreased at low rates of harvest. Our estimates of harvesting rates at maximum sustainable yield differed from those of previous investigations, perhaps because researchers used different estimates of demographic parameters, models of population dynamics, and spatial extent than we did. Good demographic knowledge and careful identification of the spatial extent of interest increases confidence in assessments and monitoring of the effects of harvesting. Our general sensitivity analysis improved understanding of harvesting effects on metapopulation dynamics and allowed qualitative assessment of the probability of extirpation of poorly studied species.     

Progress in global ecological modelling

The development of ecological modelling on global level since the middle of the 19th century is first reviewed, including application of statistical analysis, introduction of logistic curve, earth surface modeling, systems ecology, computer-oriented mathematical models and spatially explicit models. Finally, we discuss problems existing in ecological modelling on global level.     

Effectiveness of Multi‐Site Weather Generator for Hydrological Modeling1

Khalili, Malika, François Brissette, and Robert Leconte, 2011. Effectiveness of Multi‐site Weather Generator for Hydrological Modeling. Journal of the American Water Resources Association (JAWRA) 1‐12. DOI: 10.1111/j.1752‐1688.2010.00514.x Abstract: A multi‐site weather generator has been developed using the concept of spatial autocorrelation. The multi‐site generation approach reproduces the spatial autocorrelations observed between a set of weather stations as well as the correlations between each pair of stations. Its performance has been assessed in two previous studies using both precipitation and temperature data. The main objective of this paper is to assess the efficiency of this multi‐site weather generator compared to a uni‐site generator with respect to hydrological modeling. A hydrological model, known as Hydrotel, was applied over the Chute du Diable watershed, located in the Canadian province of Quebec. The distributed nature of Hydrotel accounts for the spatial variations throughout the watershed, and thus allows a more in‐depth assessment of the effect of spatially dependent meteorological input on runoff generation. Simulated streamflows using both the multi‐site and uni‐site generated weather data were statistically compared to flows modeled using observed data. Overall, the hydrological modeling using the multi‐site weather generator significantly outperformed that using the uni‐site generator. This latter combined to Hydrotel resulted in a significant underestimation of extreme streamflows in all seasons.     

CLIMATE CHANGE AND EXTRATROPICAL STORMINESS IN THE UNITED STATES: AN ASSESSMENT1

ABSTRACT: Climate change due to enrichment of the atmosphere with carbon dioxide is projected to change the circulation of the atmosphere, increase its moisture content, warm the surface layers, and increase precipitation. Extratropical storms are the intermediate agent in mid-latitudes between changes in the circulation of the atmosphere and surface water resources. The climatology of extratropical storms for the period 1885–1996 is presented, and major changes in storminess are detected across much of North America. General Circulation Model (GCM) projections of storm frequency and storm track are found to have little in common with the observed pattern of storms and evidence no systematic changes in response to an enrichment of the atmosphere with carbon dioxide.     

Construction of evolving models for the environmental evaluation of innovative sub-systems based on a hierarchical agglomerative clustering

This paper deals with simplifying the environmental evaluation of an innovative sub-system related to the future complex system that will include it, by using evolving generic models built on a limited number of characteristics. For a complex system range, the evolving approach of the environmental modelling aims to generate a learning dynamics, to avoid the paralysing complexity induced in design by the valuation of many components according to many impact categories. Applied to the automotive sector, dendrograms are made with results of life cycle assessments (LCA) of 17 vehicles for 4 environmental indicators and on 3 life cycle steps. In an iterative process, a limit condition threshold on the resulting relative errors aims to cluster the vehicles. First, several calculation methods of dendrograms are tested. Second, the influence of the limit condition on the models is observed. Lastly, by simulating the vehicle population increase, the modelling capacity to evolve is tested. Five vehicle characteristics are sufficient to identify a model to be equivalent to the future vehicle. While the number of clusters is increased to simplify their identification with the system characteristics, the relative error variability increases too. The generic models are stable when adding LCA's results.     

Models of taiga-steppe communities on the western coast of Lake Baikal

As a result of monitoring spatial changes in the cenotic structure of plant communities at the taiga-extrazonal steppe boundary on the western coast of Lake Baikal, models of taiga-steppe communities reflecting the formation, dynamics, and genesis of forests in the taiga zone have been constructed. Changes in the species composition of communities, mesophytization of steppes, the expansion of moss synusiae characteristic of polydominant dark conifer and light conifer taiga forests, active forest invasion into steppe areas, and the presence of dark conifer tree species in light conifer forests have been revealed.     

A lagrangian dispersion model for calculating concentration distribution within a built-up domain

A Lagrangian model to study the dispersion of pollutants between urban buildings is described. The flow field is supplied by an objective analysis (Rockle (1990) Ph.D. thesis, Vom Fachbereich Mechanik, der Technischen Hochschule Darmstadt, Germany) and is adjusted to satisfy the continuity equation. From the resulting; mass consistent field the Lagrangian diffusion parameters are eliminated. A 3-D Lagrangian diffusion model in a nonhomogeneous field is applied to calculate the pollutant distribution between the buildings. Several examples are studied and compared to wind tunnel measurements.