Considerations for the use of SADIE statistics to quangify spatial patterns

The SADIE methodology has recently been developed to quangify spatial patterns, particularly in determining the randomness of observed patterns, estimating patches and gaps, and quangifying correlation between species. We used argificially generated data sets to investigate the relationship of the SADIE pattern and association statistics with patch number and spatial positions of the patches. Results showed that SADIE statistics are critically dependent on the absolute positions of quadrat counts, and not just on their relative positions. In particular, degree of patchiness increased as the patch was displaced away from the centre. Therefore, the dependence of SADIE statistics on absolute sampling positions should be taken into consideration when using and interpreting SADIE-based results.     

遗传算法支持下土地利用空间分形特征尺度域的识别

针对土地利用空间分形特征只存在于有限尺度域的现象,采用无标度区内离散点拟合的离差平方和平均值最小作为目标函数,提出了一种基于遗传算法的土地利用空间分形特征尺度域的识别方法,用于准确计算分形维数的有效区间范围。以武汉市武昌区水域空间分形特征为例,利用Quickbird多光谱遥感影像提取土地利用空间信息,重点讨论了基于遗传算法识别土地利用空间分形特征尺度域范围的总体思路、适应度函数和遗传算子等环节;然后分别从测定系数、标准差和无标度区间3个角度,将其同人工判断法、相关系数法以及强化系数法进行对比讨论;并结合研究区域实际的水域空间分布格局,分析不同方法计算所得半径维数的合理性。结果表明,土地利用分形特征尺度域的范围对分形维数计算结果有较大影响;相对于传统计算方法来说,遗传算法在尺度无标度区间识别上具有更高的精度,可以为土地利用空间格局分形特征的研究提供客观指导意见。     

Quartet mapping and the extent of lateral transfer in bacterial genomes

Several recent analyses have used quartet-based methods to assess the congruence among phylogenies derived for large sets of genes from prokaryotic genomes. The principal conclusion from these studies is that lateral gene transfer (LGT) has blurred prokaryotic phylogenies to such a degree that the darwinian scheme of treelike evolution might be abandoned in favor of a net or web. Here, we focus on one of these methods, quartet mapping, and show that its application can lead to overestimation of the extent of inferred LGT in prokaryotes, particularly when applied to distantly related taxa.     

The spatial distribution of soils across Europe: A fractal approach

In this work we investigate the applicability of fractal modeling to the soil surface system in Europe, as described by the European Soil Database (V2.0) and the soil classification of the World Reference Base [FAO, 1999. World Reference Base for Soil Resources. ISSS–ISRIC–FAO, Rome, World Soil Resources Report No. 84]. Firstly, we observe the power law patterns of the distribution of pedotaxa as well as their pedorichness–area relationships. After this, we consider the 45 most abundant soils that cover 92% of the surface of Europe and estimate the box-counting fractal dimension of the areas covered by each of the pedotaxa within three orders of magnitude. Our analysis shows a remarkable scaling behavior of soil distribution and strongly suggests the fractal nature of pedotaxa distribution across Europe. These findings lead us to propose that considering the pedotaxa fractal dimension could play an important role in the analysis of the complexity of European soil systems.     

The lateral extent of the subsidy from an upland stream to riparian lycosid spiders

Adult aquatic insects emerging from streams can subsidize riparian food webs, but little is known of the spatial extent of these subsidies. Stable isotope (¹⁵N) enrichment of aquatic insects, principally a species of stonefly (Plecoptera: Leuctridae), emerging from an upland stream was used to trace the subsidy from the stream ecosystem to riparian spiders (Lycosidae). The downstream profile of spider δ¹⁵N correlated closely with that of adult stoneflies, indicating that they were deriving nutrition from aquatic sources. The contribution of adult aquatic insects to spider diets was determined using a two-source mixing model. Adult aquatic insects made up over 40% of spider diets adjacent to the stream, but <1% at 20 m from the stream. Enrichment of riparian spiders declined exponentially with distance from the stream channel. Aquatic-terrestrial subsidies were spatially restricted, but locally important, to riparian lycosid spiders at the study site.     

Disruption of state estimation in the human lateral cerebellum

The cerebellum has been proposed to be a crucial component in the state estimation process that combines information from motor efferent and sensory afferent signals to produce a representation of the current state of the motor system. Such a state estimate of the moving human arm would be expected to be used when the arm is rapidly and skillfully reaching to a target. We now report the effects of transcranial magnetic stimulation (TMS) over the ipsilateral cerebellum as healthy humans were made to interrupt a slow voluntary movement to rapidly reach towards a visually defined target. Errors in the initial direction and in the final finger position of this reach-to-target movement were significantly higher for cerebellar stimulation than they were in control conditions. The average directional errors in the cerebellar TMS condition were consistent with the reaching movements being planned and initiated from an estimated hand position that was 138 ms out of date. We suggest that these results demonstrate that the cerebellum is responsible for estimating the hand position over this time interval and that TMS disrupts this state estimate.     

Dimensional statistics for estimation of lung volumes

The theory of dimension has been widely used in physics to check the validity of formulae. This theory has not been used more frequently in statistics as compared to physics for development of various prediction formulae/equations in applied physiology. An attempt has, therefore, been made in the present investigation to evolve formulae for estimation of lung volumes from cubic function of height based on dimensional considerations in boys and girls 8-13 and 16-21 years of age.     

A three-layer model of natural image statistics

An important property of visual systems is to be simultaneously both selective to specific patterns found in the sensory input and invariant to possible variations. Selectivity and invariance (tolerance) are opposing requirements. It has been suggested that they could be joined by iterating a sequence of elementary selectivity and tolerance computations. It is, however, unknown what should be selected or tolerated at each level of the hierarchy. We approach this issue by learning the computations from natural images. We propose and estimate a probabilistic model of natural images that consists of three processing layers. Two natural image data sets are considered: image patches, and complete visual scenes downsampled to the size of small patches. For both data sets, we find that in the first two layers, simple and complex cell-like computations are performed. In the third layer, we mainly find selectivity to longer contours; for patch data, we further find some selectivity to texture, while for the downsampled complete scenes, some selectivity to curvature is observed.     

The use of bootstrap resampling to assess the uncertainty of cooper statistics

The predictive abilities of two-group classification models (CMs) are often expressed in terms of their Cooper statistics. These statistics are often reported without any indication of their uncertainty, making it impossible to judge whether the predicted classifications are significantly better than the predictions made by a different CM, or whether the predictive performance of the CM exceeds predefined performance criteria in a statistically significant way. Bootstrap resampling routines are reported that provide a means of expressing the uncertainty associated with Cooper statistics. The usefulness of the bootstrapping routines is illustrated by constructing 95% confidence intervals for the Cooper statistics of four alternative skin-corrosivity tests (the rat skin transcutaneous electrical resistance assay, EPISKIN, Skin(2) and CORROSITEX), and four two-step sequences in which each in vitro test is used in combination with a physicochemical test for skin corrosion based on pH measurements.     

Characterizing fishing effort and spatial extent of coastal fisheries

Biodiverse coastal zones are often areas of intense fishing pressure due to the high relative density of fishing capacity in these nearshore regions. Although overcapacity is one of the central challenges to fisheries sustainability in coastal zones, accurate estimates of fishing pressure in coastal zones are limited, hampering the assessment of the direct and collateral impacts (e.g., habitat degradation, bycatch) of fishing. We compiled a comprehensive database of fishing effort metrics and the corresponding spatial limits of fisheries and used a spatial analysis program (FEET) to map fishing effort density (measured as boat-meters per km2) in the coastal zones of six ocean regions. We also considered the utility of a number of socioeconomic variables as indicators of fishing pressure at the national level; fishing density increased as a function of population size and decreased as a function of coastline length. Our mapping exercise points to intra and interregional 'hotspots' of coastal fishing pressure. The significant and intuitive relationships we found between fishing density and population size and coastline length may help with coarse regional characterizations of fishing pressure. However, spatially-delimited fishing effort data are needed to accurately map fishing hotspots, i.e., areas of intense fishing activity. We suggest that estimates of fishing effort, not just target catch or yield, serve as a necessary measure of fishing activity, which is a key link to evaluating sustainability and environmental impacts of coastal fisheries.     

空间幅度变化对景观格局分析的影响

景观格局指数是量化描述景观格局特征的主要方法之一,各种格局指数的尺度依赖性使比较分析景观格局特征和尺度推绎复杂化,分析不同指数随空间幅度变化的一般行为有助于景观格局分析结果的解释和降低空间尺度推绎的复杂性。研究以2种真实景观和27种模拟景观为分析对象,考查了16种常用的景观水平格局指数随空间幅度变化行为。根据这些指数因幅度变化行为可预测性把它们分为两类：第1类随幅度变化可预测性强,指数与幅度之间的关系可用简单的函数关系来表达;这类指数包括缀块数、边界总长、景观形状指数和缀块丰度密度;前两者随幅度增加呈幂函数形式增加,而缀块丰度密度随幅度增加呈幂函数下降,景观形状指数随幅度增加呈直线增加。第2类指数随幅度变化的可预测性较差,指数随幅度的变化存在多种可能(不同形式的增加、减小或保持不变),不可用一种或多种简单的函数关系来描述所有的情况。这类指数包括缀块丰度、缀块密度、边界密度、最大缀块指数、平均缀块面积、缀块面积标准差、缀块面积变异系数、平均缀块形状指数、面积加权平均缀块形状指数、双对数回归分维数、聚集度指数与Shannon多样性指数。第2类指数随幅度的变化行为受景观格局特征和指数本身算法的影响。总体上来说,第2类格局指数随幅度变化呈折线增加或减小;但当景观的缀块类型较多、各类型优势度比较均等、空间分布格局比较随机时,它们随幅度变化形为的可预测性增加,随幅度增加的函数关系主要有3种：幂函数减小、对数函数增加或直线增加,因指数和格局特征不同而异。研究的结果在揭示了常用景观指数随幅度变化的一般关系外,也启示我们在进行景观格局的比较分析,比较景观的幅度应相同或采用尺度效应图(scalograms)更有效。