Evaluating regional water security through a freshwater ecosystem service flow model: A case study in Beijing-Tianjian-Hebei region,China

Freshwater ecosystem service is essential to human’s survival and development. Many studies have documented the spatial differences in the supply and demand of ecosystem services and proposed the concept of ecosystem services flows. However, few studies characterize freshwater ecosystem service flow quantitatively. Therefore, our paper aims to quantify the effects of freshwater ecosystem service flow on downstream areas. We developed a freshwater ecosystem service flow model and applied it in the Beijing–Tianjin–Hebei (BTH) region, China, for the year of 2000, 2005, and 2010. We assessed the regional water security with an improved freshwater security index by integrating freshwater service provision, consumption and flow; and found that most areas of the BTH region (69.2%) were affected by upstream freshwater flows. The areas achieving water security in the region also expanded to 66.9%, 66.1%, and 71.3%, which were 6.4%, 6.8% and 5.7% increments compared to no-flow situation, in 2000, 2005 and 2010, respectively. Setting quota for human water consumption is suggested to further improve water security. These results highlight the need to fully understand the connections between distant freshwater ecosystem service provision and local freshwater ecosystem service consumption. This approach may also help managers to choose more sustainable strategies for critical freshwater resource management across different regions.     

The scale of analysis determines the spatial pattern of woody species diversity in the Mediterranean environment

We examine the spatial pattern of woody species diversity at different scales, in two sites of Mt. Holomontas in northern Greece, which falls within the transitional zone between temperate forests and Mediterranean-type ecosystems. We investigate how diversity is distributed in space and whether the perceived pattern changes with the scale of observation. We use two different metrics of diversity: species richness and species turnover. Our main finding is that the spatial pattern of diversity changes with the scale of observation or analysis. For a given scale, the pattern of species richness (alpha diversity) is negatively correlated with the pattern of species turnover (beta diversity). Species-rich areas have more species in common with their neighbors than species-poor areas. The between-scale disparity of the spatial pattern of diversity may be a general feature of ecological systems. For this to be validated, studies with different groups of species in different biomes and in different biogeographical areas are required; our study contributes to this direction providing evidence that this holds true for woody species in Mediterranean communities. Finally, we discuss how these findings might affect important issues in theoretical and applied ecology, such as identifying the environmental factors driving biodiversity.     

Conceptual design and implantation of an external fixator with improved mobility for knee rehabilitation

A hinged external fixator is used to allow early knee rehabilitation in case of injury or trauma, as an alternative approach to immobilization. It is mainly adopted for the treatment of dislocations, which involve tearing of the ligaments, and it basically consists of two links connected to each other by a revolute joint. Each link is fixed to the femur and tibia via pin fixation, and the revolute joint is approximately aligned to the knee flexion-extension (FE) axis. The advantage in its implantation is to protect ligament reconstruction, while allowing for an aggressive rehabilitation. Traditional fixators only accommodate the functional flexion movement in a limited range, i.e. where the anatomical movement is closer to a planar circular trajectory. This paper presents the conceptual design and implantation procedure of a double-axis fixator, which accommodates both FE and longitudinal internal-external rotation. The procedure is based on accurate knee kinematics measurements and on computer-aided multibody simulations to assist clinicians in the implantation. An experimental test is presented using an artificial knee, and guidelines are given for in vitro studies. The proposed technique may allow for a better understanding of knee kinematics and have the potential advantage to increase the range of motion in postoperative rehabilitation.     

Correcting for finite spatial scales of self-similarity when calculating fractal dimensions of real-world structures

Fractal geometry is a potentially valuable tool for quantitatively characterizing complex structures. The fractal dimension (D) can be used as a simple, single index for summarizing properties of real and abstract structures in space and time. Applications in the fields of biology and ecology range from neurobiology to plant architecture, landscape structure, taxonomy and species diversity. However, methods to estimate the D have often been applied in an uncritical manner, violating assumptions about the nature of fractal structures. The most common error involves ignoring the fact that ideal, i.e. infinitely nested, fractal structures exhibit self-similarity over any range of scales. Unlike ideal fractals, real-world structures exhibit self-similarity only over a finite range of scales.Here we present a new technique for quantitatively determining the scales over which real-world structures show statistical self-similarity. The new technique uses a combination of curve-fitting and tests of curvilinearity of residuals to identify the largest range of contiguous scales that exhibit statistical self-similarity. Consequently, we estimate D only over the statistically identified region of self-similarity and introduce the finite scale- corrected dimension (FSCD). We demonstrate the use of this method in two steps. First, using mathematical fractal curves with known but variable spatial scales of self-similarity (achieved by varying the iteration level used for creating the curves), we demonstrate that our method can reliably quantify the spatial scales of self-similarity. This technique therefore allows accurate empirical quantification of theoretical Ds. Secondly, we apply the technique to digital images of the rhizome systems of goldenrod (Solidago altissima). The technique significantly reduced variations in estimated fractal dimensions arising from variations in the method of preparing digital images. Overall, the revised method has the potential to significantly improve repeatability and reliability for deriving fractal dimensions of real-world branching structures.     

广州地区淡水水体尿素的分布特征

近年来,随着农业的发展,化学肥料尿素的使用量逐年攀升,由于土壤中氮肥的流失,导致水体中尿素含量偏高,对浮游植物的生长繁殖起到了重要的作用。于2007年8月～2008年7月对广州市区、从化市、花都区和增城区四个地区的具有代表性的河涌、河流、人工湖和水库等47个样点的尿素含量进行了一年的监测。结果表明,这四个地区河涌、河流、人工湖和水库都不同程度的受到了尿素的污染,其中广州市区尿素污染最严重,其次是花都区和增城区,污染最轻的是从化市;从水体类型来看,人工湖和大多数水库尿素污染较轻,而人口居住较密集地区和农田附近的河涌和河流污染较严重,可能与人类活动和农业生产关系较大。     

Local host competition in the evolution of virulence

The evolution of parasite life histories should usually have correlated effects on host survivorship and/or reproductive success. For example, parasites that reproduce more rapidly might be expected to cause greater reductions in host fitness. Important theoretical advances have recently been made on virulence evolution, but the results are not always consistent. Here I compare two models [ Q. Rev. Biol. 71 (1996) 37 ; Q. Rev. Biol. 75 (2000) 261 ] on the evolution of virulence that get qualitatively different results with respect to the effects of coinfection. I also construct a third model that attempts to connect these two formulations. The results suggest that parasite growth rates should increase as local host competition increases, unless relatedness is at equilibrium. In addition, the qualitative effect of adding coinfections on parasite growth rates depends critically on how the number of coinfections affects transmission success.     

Efficiency of using spatial analysis in first-generation coastal Douglas-fir progeny tests in the US Pacific Northwest

Single-trial and across-trial spatial analyses using autoregressive error structures were conducted for growth traits based on 1,146 data sets from 275 Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] progeny trials in 45 first-generation breeding zones in the US Pacific Northwest. The breeding zones encompassed a wide range of latitude, longitude, and elevation. Efficiency of using spatial analysis in reducing variation due to site heterogeneity, estimating genetic parameters, and increasing prediction accuracy was compared among different experimental designs, traits, assessment ages, and tree spacings. More than 97% of the data sets showed significant model improvement with spatial analysis, and height showed more improvement than diameter or volume. Spatial analysis on average removed 14~34% of residual variance due to spatial heterogeneity, which resulted in an up to 20% increase in accuracy of breeding value prediction. The coefficient of variation decreased substantially due to spatial adjustment. Rank correlation between predicted gains before and after spatial analysis was about 0.96, and spatial analysis had little effect on the average predicted gain of the top 20% of parents. We did not observe substantial geographic trends in improvements due to spatial adjustment. Across-site spatial analysis had almost no effect on genotype-by-environment interaction but tended to increase among-trial heterogeneity of residual variance. Two different methods for across-trial spatial analysis were compared and discussed.