The evolution of intermediate castration virulence and ant coexistence in a spatially structured environment

Theory suggests that spatial structuring should select for intermediate levels of virulence in parasites, but empirical tests are rare and have never been conducted with castration (sterilizing) parasites. To test this theory in a natural landscape, we construct a spatially explicit model of the symbiosis between the ant-plant Cordia nodosa and its two, protecting ant symbionts, Allomerus and Azteca . Allomerus is also a castration parasite, preventing fruiting to increase colony fecundity. Limiting the dispersal of Allomerus and host plant selects for intermediate castration virulence. Increasing the frequency of the mutualist, Azteca , selects for higher castration virulence in Allomerus , because seeds from Azteca -inhabited plants are a public good that Allomerus exploits. These results are consistent with field observations and, to our knowledge, provide the first empirical evidence supporting the hypothesis that spatial structure can reduce castration virulence and the first such evidence in a natural landscape for either mortality or castration virulence.     

An evaluation of semi‐automated methods for collecting ecosystem‐level data in temperate marine systems

Historically, marine ecologists have lacked efficient tools that are capable of capturing detailed species distribution data over large areas. Emerging technologies such as high‐resolution imaging and associated machine‐learning image‐scoring software are providing new tools to map species over large areas in the ocean. Here, we combine a novel diver propulsion vehicle (DPV) imaging system with free‐to‐use machine‐learning software to semi‐automatically generate dense and widespread abundance records of a habitat‐forming algae over ~5,000 m² of temperate reef. We employ replicable spatial techniques to test the effectiveness of traditional diver‐based sampling, and better understand the distribution and spatial arrangement of one key algal species. We found that the effectiveness of a traditional survey depended on the level of spatial structuring, and generally 10–20 transects (50 × 1 m) were required to obtain reliable results. This represents 2–20 times greater replication than have been collected in previous studies. Furthermore, we demonstrate the usefulness of fine‐resolution distribution modeling for understanding patterns in canopy algae cover at multiple spatial scales, and discuss applications to other marine habitats. Our analyses demonstrate that semi‐automated methods of data gathering and processing provide more accurate results than traditional methods for describing habitat structure at seascape scales, and therefore represent vastly improved techniques for understanding and managing marine seascapes.     

Modeling WEPP erodibility parameters in calcareous soils in northwest Iran

Modeling soil detachment rates at the regional scale is important for better understanding of the processes of erosion and the development of erosion models. Soil erodibility is an important factor for predicting soil loss, but its direct measurement at the watershed scale is difficult, time-consuming and costly. This study used stepwise multiple-linear regression (MLR) and artificial neural networks (ANNs) to model Water Erosion Prediction Project (WEPP) soil erodibility parameters, including the baseline inter-rill erodibility (K_ib), baseline rill erodibility (K_rb) and critical shear stress (τ_cb) of cropland conditions in calcareous soils of northwest Iran. Simulated inter-rill and rill erosion experiments were conducted at 100 locations with three replications. K_ib, K_rb and τ_cb and basic soil properties were measured at each location. Auxiliary variables related to soil erodibility were derived from a Landsat 7 satellite image and a 30 m × 30 m digital elevation model (DEM). MLR and ANN models were employed to predict K_ib, K_rb and τ_cb using two groups of input variables: i) more easily measurable basic soil properties (pedo-transfer functions (PTFs)) and ii) more easily measurable basic soil properties and auxiliary data (soil spatial prediction functions (SSPFs)). The results indicated that the WEPP models performed poorly in comparison to the derived models. PTFs and SSPFs generated from ANN models provided more reliable predictions than the MLR models. ANN-based SSPF models yielded the best results (with the highest R² and lowest RMSE values) for predicting Kib and Krb. ANN-based PTF model performed reasonably well for predicting τ_cb. These results show that information from terrain attributes and remote sensing data are potential auxiliary variables for improving prediction of soil erodibility parameters.     

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.     

2001-2010年疏勒河流域植被净初级生产力时空变化及其与气候因子的关系

通过改进的光能利用率CASA模型估算2001-2010年间疏勒河流域陆地生态系统的净第一性生产力（NPP），采用线性趋势分析、变异系数和Hurst指数等方法，分析了NPP的时空变化特征及其与气候因子的相关性。结果表明：①疏勒河流域NPP的空间分布具有明显差异，空间上呈现西北低、东南高的趋势，且具有较明显的经向"条带"分布特征，2001-2010年，NPP平均值为102.26 gC m^-2 a^-1。②2001-2010年，疏勒河流域NPP总体呈增长趋势，年际波动较大，NPP明显增加的区域占总面积25.15%，明显减小的区域约占11.93%。③Hurst指数分析显示，疏勒河流域NPP变化的同向特征强于反向特征，其中持续改善地区占总面积的78.3%，21.7%的区域将由改善转为退化。④在年尺度上，降水是植被NPP变化的主要影响因素，NPP与降水呈弱的正相关关系，与温度相关性不显著；在月尺度上，温度是NPP变化的主要控制因子。疏勒河流域NPP对气候因子不存在明显的时滞和累积效应。     

On Connectedness of a Two-way Elimination of Heterogeneity Design

For some subclass of a two-way elimination of heterogeneity design, necessary and sufficient conditions are established for row-connectedness and column-connectedness of a design to imply its connectedness.     

基于地统计学的新疆棉田烟粉虱(Bemisia tabaci (Gennadius))危害动态与时空分布

应用地统计学(GS)的原理与方法研究了外来入侵有害生物烟粉虱(Bemisia tabaci (Gennadius))为害新疆棉田的时空动态,并与经典统计学进行对比分析.两种方法一致表明,烟粉虱成虫在空间上呈聚集分布的格局,而各时期成虫的聚集程度依据空间变异随机程度所占的比例不同而不同.经频次分布检验,以零频率法参数拟合的负二项分布来表达其空间分布型最为合适.运用GS的分析方法,进一步得到种群分布面积变化与扩散的趋势,并依此对昆虫种群的扩散模型进行模拟.棉田烟粉虱成虫在田间7～8月份均存在一定的空间相关性,随机程度为19.22%～49.99%;空间相关距离(相关程)在一个月内从32m急速增至6372m,随后在2000～3000m的范围波动.从整个发生过程看出,烟粉虱从越冬场所顺风侵入大田后,迁飞扩散在很大程度上受风向的影响,属于典型的借助风力扩散的昆虫,其在棉田的垂直分布则与吐鲁番地区独特的暖温带大陆性干旱荒漠气候特征有关.顺风扩散时多从棉株上部叶片开始危害, 而逆风扩散时从棉株中、下部叶片危害.烟粉虱在棉株上建立稳定种群后,中、下部虫口密度要略高于上部, 这是烟粉虱对吐鲁番地区特殊气候的适应.