闽江河口湿地土壤盐分的空间分异与集聚特征

探究河口湿地土壤盐分的空间异质性,揭示分异格局下的空间集聚特征,对河口湿地的可持续发展具有重要意义。本文以福州市闽江河口湿地的Landsat 8遥感影像、数字高程模型和地面实测土壤盐分为数据源,利用相关性分析与主成分分析法选取显著性环境因子,去除变量间的共线性,分别采用支持向量机回归克里格法(SVROK)和回归克里格法(RK)分析了土壤盐分空间异质性,在基础上运用空间自相关法定量描述了土壤盐分空间集聚特征。结果表明: 通过主成分分析提取出3个主成分,可解释数据总方差的85%,反映植被覆盖、土壤属性和地形状况等综合变化信息,并保留原始变量的大部分信息;土壤盐分及其插值残差的空间变异受结构性因素和随机性因素的影响,采用主成分为自变量所建立的SVROK模型能更为精准地体现土壤盐分 “北高南低”的空间异质特征;土壤盐分的Moran I大于0.5,具有显著的空间正相关,空间集聚程度较高,呈现出“高值集聚、低值广布、低值包围高值”的空间集聚特征。     

Spatial analysis of egg distribution and geographic changes in the spawning habitat of the Brazilian sardine Sardinella brasiliensis

This paper establishes the spawning habitat of the Brazilian sardine Sardinella brasiliensis and investigates the spatial variability of egg density and its relation with oceanographic conditions in the shelf of the south‐east Brazil Bight (SBB). The spawning habitats of S. brasiliensis have been defined in terms of spatial models of egg density, temperature–salinity plots, quotient (Q) analysis and remote sensing data. Quotient curves (Q_C) were constructed using the geographic distribution of egg density, temperature and salinity from samples collected during nine survey cruises between 1976 and 1993. The interannual sea surface temperature (SST) variability was determined using principal component analysis on the SST anomalies (SSTA) estimated from remote sensing data over the period between 1985 and 2007. The spatial pattern of egg occurrences in the SBB indicated that the largest concentration occurred between Paranaguá and São Sebastião. Spawning habitat expanded and contracted during the years, fluctuating around Paranaguá. In January 1978 and January 1993, eggs were found nearly everywhere along the inner shelf of the SBB, while in January 1988 and 1991 spawning had contracted to their southernmost position. The SSTA maps for the spawning periods showed that in the case of habitat expansion (1993 only) anomalies over the SBB were zero or slightly negative, whereas for the contraction period anomalies were all positive. Sardinella brasiliensis is capable of exploring suitable spawning sites provided by the entrainment of the colder and less‐saline South Atlantic Central Water onto the shelf by means of both coastal wind‐driven (to the north‐east of the SBB) and meander‐induced (to the south‐west of the SBB) upwelling.     

Canine filariosis in Umbria: an update of the occurrence one year after the first observation of autochthonous foci

Following the first observation of two autochthonous foci of canine filariosis occurred in Umbria region in the year 2001, a survey on prevalence and risk factors was conducted 12 months later to better understand the actual entity of the Dirofilaria problem in Umbria region. Blood samples were collected between January and December 2002 from 2406 dogs living in a total of 7 towns located in the identified areas at risk. Blood samples were tested by a modified Knott's technique to evaluate the microfilaraemia and, by a commercial ELISA kit, to detect in the sera adult antigens of D. immitis. The results were subject to statistical analysis. A total of 439 dogs were found to be infected. The true prevalence (LC 95%) was of 18%. Microfilariae of D. immitis were detected in 286 dogs (13%) while 112 dogs (6%) showed only microfilariae of D. repens and 41 dogs (1.6%) microfilariae of both D. immitis and D. repens. The prevalence ratio (PR) for each species of Dirofilaria (LC 95%) calculated in association with different risk factors (age, sex, use, outdoor night status, position, living together with other dogs, breed) and the statistical significance between the risk factors and the presence/absence of the infection, evaluated for each species of Dirofilaria, are discussed.     

Examining stability of independent component analysis based on coefficient and component matrices for voxel-based morphometry of structural magnetic resonance imaging

Independent component analysis (ICA) on group-level voxel-based morphometry (VBM) produces the coefficient matrix and the component matrix. The former contains variability among multiple subjects for further statistical analysis, and the latter reveals spatial maps common for all subjects. ICA algorithms converge to local optimization points in practice and the mostly applied stability investigation approach examines the stability of the extracted components. We found that the practically stable components do not guarantee to produce the practically stable coefficients of ICA decomposition for the further statistical analysis. Consequently, we proposed a novel approach including two steps: (1), the stability index for the coefficient matrix and the stability index for the component matrix were examined, respectively; (2) the two indices were multiplied to analyze the stability of ICA decomposition. The proposed approach was used to study the sMRI data of Type II diabetes mellitus group and the healthy control group (HC). Group differences in VBM were found in the superior temporal gyrus. Besides, it was revealed that the VBMs of the region of the HC group were significantly correlated with Montreal Cognitive Assessment (MoCA) describing the level of cognitive disorder. In contrast to the widely applied approach to investigating the stability of the extracted components for ICA decomposition, we proposed to examine the stability of ICA decomposition by fusion the stability of both coefficient matrix and the component matrix. Therefore, the proposed approach can examine the stability of ICA decomposition sufficiently.     

Susceptibility of mosquitoes in central Taiwan to natural infections of Dirofilaria immitis

From October 1997 to September 1998, 3085 Culex quinquefasciatus (Say) (Diptera: Culicidae), 584 Cx. tritaeniorhynchus (Giles) (Diptera: Culicidae), 392 Cx. annulus (Theobald) (Diptera: Culicidae), 374 Aedes albopictus (Skuse) (Diptera: Culicidae) and 102 Armigeres subalbatus (Coquillet) (Diptera: Culicidae) were collected and examined for Dirofilaria immitis (Leidy) (Spirurida: Filariidae) infection. However, only Cx. quinquefasciatus and Ae. albopictus were infected, with a prevalence of 4.28% and 3.74%, respectively. The intensity of D. immitis found in Ae. albopictus (3.43 larvae/mosquito) was higher than that found in Cx. quinquefasciatus (2.89 larvae/mosquito). After being fed with canine blood containing 7500 microfilariae (mf) per mL, Cx. quinquefasciatus ingested approximately two times as many mf as Ae. albopictus (mean of 31.73 in comparison to 16.47). However, almost three times as many third-stage infective larvae developed in Ae. albopictus as in Cx. quinquefasciatus (mean of 3.25 as compared with 1.10), with a vector efficiency index (VEI) of 19.73 and 3.47, respectively. The results showed that Cx. quinquefasciatus and Ae. albopictus served as natural vectors of D. immitis in central Taiwan. Although Ae. albopictus was more efficient for heartworm transmission, Cx. quinquefasciatus may play a more prominent role on the transmission of dirofilariasis in central Taiwan.     

Host and parasite recruitment correlated at a regional scale

Drivers of large-scale variability in parasite prevalence are not well understood. For logistical reasons, explorations of spatial patterns in parasites are often performed as observational studies. However, to understand the mechanisms that underlie these spatial patterns, standardized and controlled comparisons are needed. Here, we examined spatial variability in infection of an important fishery species and ecosystem engineer, the oyster (Crassostrea virginica) by its pea crab parasite (Zaops ostreus) across 700 km of the southeastern USA coastline. To minimize the influence of host genetics on infection patterns, we obtained juvenile oysters from a homogeneous source stock and raised them in situ for 3 months at multiple sites with similar environmental characteristics. We found that prevalence of pea crab infection varied between 24 and 73 % across sites, but not systematically across latitude. Of all measured environmental variables, oyster recruitment correlated most strongly (and positively) with pea crab infection, explaining 92 % of the variability in infection across sites. Our data ostensibly suggest that regional processes driving variation in oyster recruitment similarly affect the recruitment of one of its common parasites.     

Serological and molecular studies on Dirofilaria immitis in dogs from Turkey

We estimated the prevalence of Dirofilaria immitis infection in domestic dogs in five Turkish provinces - Sakarya, Kocaeli, Ankara, Elazig and Mersin - using a commercial ELISA kit for detecting circulating antigen and a PCR test for detecting circulating microfilarial DNA. A total of 211 whole-blood and serum samples were collected from dogs of various breeds, ages and life status (owned or stray). Sample population characteristics were recorded and examined for differences in prevalence. Additionally, we collected 15 blood samples from cats (14 owned and 1 stray) from Ankara province and used PCR to detect D. immitis infection. Twenty-seven (12.8%) of 211 dog samples were positive for D. immitis antigen by ELISA. No differences in prevalence were observed by sex (female: 14.4%; male: 10.7%; P>0.05). The prevalence of D. immitis infection varied with age: 11.8% in younger dogs (0.5-2 years) and 17.5% in older dogs (3-5 years). Prevalence between stray dogs (15.2%) and owned dogs (9.3%) did not differ (P>0.05). Prevalence rates were highest in Kocaeli province (18.3%), followed by Ankara (14.8%), Sakarya (12.3%) and Mersin (10.5%) provinces. Prevalence in Elazig province was 0%. No dogs or cats had microfilarial DNA detectable by PCR.     

Revealing cryptic spatial patterns in genetic variability by a new multivariate method

Increasing attention is being devoted to taking landscape information into account in genetic studies. Among landscape variables, space is often considered as one of the most important. To reveal spatial patterns, a statistical method should be spatially explicit, that is, it should directly take spatial information into account as a component of the adjusted model or of the optimized criterion. In this paper we propose a new spatially explicit multivariate method, spatial principal component analysis (sPCA), to investigate the spatial pattern of genetic variability using allelic frequency data of individuals or populations. This analysis does not require data to meet Hardy-Weinberg expectations or linkage equilibrium to exist between loci. The sPCA yields scores summarizing both the genetic variability and the spatial structure among individuals (or populations). Global structures (patches, clines and intermediates) are disentangled from local ones (strong genetic differences between neighbors) and from random noise. Two statistical tests are proposed to detect the existence of both types of patterns. As an illustration, the results of principal component analysis (PCA) and sPCA are compared using simulated datasets and real georeferenced microsatellite data of Scandinavian brown bear individuals (Ursus arctos). sPCA performed better than PCA to reveal spatial genetic patterns. The proposed methodology is implemented in the adegenet package of the free software R.     

MORPHOLOGICAL EVOLUTION IN MUROID RODENTS I. CONSERVATIVE PATTERNS OF CRANIOMETRIC COVARIANCE AND THEIR ONTOGENETIC BASIS IN THE NEOTROPICAL GENUS ZYGODONTOMYS

Analyses of craniodental measurement data from 15 wild-collected population samples of the Neotropical muroid rodent genus Zygodontomys reveal consistent patterns of relative variability and correlation that suggest a common latent structure. Eigenanalysis of each sample covariance matrix of logarithms yields a first principal component that accounts for a large fraction of the total variance. Variances of subsequent sample principal components are much smaller, and the results of bootstrap resampling together with asymptotic statistics suggest that characteristic roots of the covariance matrix after the first are seldom distinct. The coefficients of normalized first principal components are strikingly similar from sample to sample: inner products of these vectors reveal an average between-sample correlation of 0.989, and the mean angle of divergence is only about eight degrees. Since first principal component coefficients identify the same contrasts among variables as comparisons of relative variability and correlation, we conclude that a single factor accounts for most of the common latent determination of these sample dispersions. Analyses of variance based on toothwear (a coarse index of age) and sex in the wild-collected samples, and on known age and sex in a captive-bred population, reveal that specimen scores on sample first principal components are age- and sex-dependent; residual sample dispersion, however, is essentially unaffected by age, sex, or age × sex interaction. The sample first principal component therefore reflects the covariance among measured dimensions induced by general growth, and its coefficients are interpretable as exponents of postnatal growth allometry. Path-analytic models that incorporate prior knowledge of the equivalent allometric effects of general growth within these samples can be used to decompose the between-sample variance by factors corresponding to other ontogenetic mechanisms of form change. The genetic or environmental determinants of differences in sample mean phenotypes induced by such mechanisms, however, can be demonstrated only by experiment.     

Survey of canine heartworm in the city of Recife, Pernambuco, Brazil.

Six hundred and eleven random-source dogs (338 male, 273 female) one year of age or older, from six sections of the city of Recife, Pernambuco, were examined antemortem for circulating microfilariae Dirofilaria immitis and Dipetalonema reconditum adult heartworm (D. immitis) antigen, and examined postmortem for adult heartworms. The prevalence of heartworm infection was 2.3% (14/611), as determined by necropsy for adult worms, and 1% (6/611) had circulating microfilariae of D. immitis; thus, 57.1% of the heartworm-infected dogs had occult infections. The results of serological testing indicated that 1.3% (8/611) of the dogs were positive for adult heartworm antigen. A total of 42 (6.9%) of the dogs had microfilariae of D. reconditum; 40 of these had only D. reconditum and two additional dogs had microfilariae of both species, D. immitis and D. reconditum.     

Spatial Analysis of Antibiotic Resistance Along Metal Contaminated Streams

The spatial pattern of antibiotic resistance in culturable sediment bacteria from four freshwater streams was examined. Previous research suggests that the prevalence of antibiotic resistance may increase in populations via indirect or coselection from heavy metal contamination. Sample bacteria from each stream were grown in media containing one of four antibiotics—tetracycline, chloramphenicol, kanamycin, and streptomycin—at concentrations greater than the minimum inhibitory concentration, plus a control. Bacteria showed high susceptibilities to the former two antibiotics. We summarized the latter two more prevalent (aminoglycoside) resistance responses and ten metals concentrations per sediment sample, by Principal Components Analysis. Respectively, 63 and 58% of the variability was explained in the first principal component of each variable set. We used these multivariate summary metrics [i.e., first principal component (PC) scores] as input measures for exploring the spatial correlation between antibiotic resistance and metal concentration for each stream sampled. Results show a significant and negative correlation between metals PC scores versus aminoglycoside resistance scores and suggest that selection for metal tolerance among sediment bacteria may influence selection for antibiotic resistance differently in sediments than in the water column. Our most important finding comes from geostatistical cross-variogram analysis, which shows that increasing metal concentration scores are spatially associated with decreasing aminoglycoside resistance scores—a negative correlation, but holds for contaminated streams only. We suspect our field results are influenced by metal bioavailability in the sediments and by a contaminant promoted interaction or “cocktail effect” from complex combinations of pollution mediated selection agents.     

Multivariate variation in feral American mink (Mustela vison) from Southern Norway

Multiple group principal component analysis was used to investigate the morphological relationships between feral American mink from three areas of Southern Norway based on 15 skull dimensions. The first principal axis calculated from the variance-covariance matrix of log-transformed data is usually interpreted as a growth axis. In the present analysis, the scores of the first principal axis of males were found to be uncorrelated with estimated age for specimens younger than seven months old, and was interpreted as a growth-free size axis. However, the second component of males was found to reflect mainly growth in the postorbital area. The first component of females was thought to reflect a mixing of growth-out and growth-in size variation. One of the reasons for separating size and size-free variation in the present work was to test whether growth-dependent size influenced the assessment of geographic variation within each sex. The scores on the components reflecting size variation (growthout and growth-in) were, however, not found to deviate significantly between the areas. Discriminant analyses run on the component scores, both with size variation included and excluded, gave the same result. In mean, the mink from Western Norway deviated significantly from the mink from Trondelag and Eastern Norway, while the mink from the two latter areas did not deviate morphometrically. The deviation found was in shape rather than in size of both sexes.     

A seasonal study of the distributions of surface state variables in Liverpool Bay. I. winter data

The physical, chemical, and biological characteristics of the surface waters of Liverpool Bay were investigated during six seasonal cruises in 1975. The winter data has been analysed to provide criteria by which spatial and temporal changes in the distributions of surface state variables during the seasonal production cycle may be judged. Surface distribution maps observed during two winter cruises (January and December) were markedly dissimilar. This temporal variability is attributed to changing circulation patterns within the Bay induced by variations in magnitude and direction of wind stress. Despite the ‘visual’ dissimilarity in spatial distributions observed on the two cruises, principal component analysis demonstrates a similar general background which is dominated by conservative physical mixing of sea and fresh waters. During winter, the spatial variability in water characteristics originated at the boundaries of the cruise path and spread internally, primarily as a consequence of the differing composition of the source waters, to the sea area. No internal sources or sinks, either anthropogenically or biologically induced, were encountered during the winter cruises.     

Prevalence of canine dirofilariasis in Taiwan

Between 1993 and 1997, 837 stray dogs from North Taiwan were necropsied and examined for dog heartworm infections. A thick smear from 20 ml of peripheral blood from each dog was also prepared and examined for microfilariae (mf). The overall prevalence of adult worms in the dog population was 57%. The prevalence of mf in 1228 house dogs from different parts of Taiwan was also determined from 20 ml of peripheral blood in the same way. The overall prevalence of mf was 25%, with a value of 30% in the main island of Taiwan, this being 15 times higher than that in the offshore islands (2%). In Taiwan, the prevalence ranged from 4% in Hualien County, East Taiwan, to 41% in Nantou County, Central Taiwan. The mf prevalences on offshore islands were 1% on Liuchiu and 2% on Lanyu. The mf density per 20 ml blood in 82 house dogs was found to be 23 mf per dog, with a range of 3-97 mf per dog. A total of 477 stray dogs were found to be infected with adult worms of Dirofilaria immitis. The mean number of 7 worms per dog was obtained, with a range of 1-55 worms per dog. These results indicate that the prevalence of canine dirofilariasis has increased in Taiwan over the past 10 years. Moreover, the prevalence may be related to the wind speed, temperature, relative humidity, and altitude in the different areas surveyed.     

A method for characterizing the biodiversity in bat pinnae as a basis for engineering analysis

A quantitative analysis of the interspecific variability between beamforming baffle shapes in the biosonar system of bats is presented. The data set analyzed consisted of 100 outer ear (pinna) shapes from at least 59 species. A vector-space representation suitable for principal component analysis (PCA) was constructed by virtue of a transform of the pinna surfaces into cylindrical coordinates. The central axis of the cylindrical transform was found by minimizing a potential function. The shapes were aligned by means of their respective axes and their center of gravity. The average pinna of the sample was a symmetrical, obliquely truncated horn. The first seven eigenvalues accounted already for two-thirds of the variability around the mean, which indicates that most of the biodiversity in the bat pinna can be understood in a more low-dimensional space. The first three principal components show that most of the variability of the bat pinna sample is in terms of opening angle, left-right asymmetry, and selective changes in width at the top or the bottom of the pinna. The beampattern effects of these individual components have been characterized. These insights could be used to design bioinspired beamforming devices from the diversity in biosonar.     

Relationship between small-scale structural variability and simulated vegetation productivity across a regional moisture gradient in southern Africa

The observed variability in vegetation structure within landscapes was used as the basis for model estimates of the range of annual productivity of landscape patches at four sites along a moisture gradient in southern Africa ranging from 879 to 365 mm mean annual rainfall. Principal components of patch‐scale variability in leaf area, woody biomass and vertical leaf profiles were derived from intensive characterization of the small‐scale spatial structure of woody vegetation at each site. For each site, the mean and extremes of the principal component distribution parameterized an ecophysiology model of vegetation productivity. Vegetation was most heterogeneous at intermediate locations along the rainfall gradient. Variability in vegetation structure led to a range of annual productivity within one site (600 mm) that accounted for 68% of the total range in mean productivity across all sites. Patch‐scale estimates of tree productivity were found to be primarily correlated to annual rainfall (r²=0.66, P=0.001) and not woody leaf area (r²=0.01, P=0.75), while grass productivity was found to be related to values of woody leaf area (r²=0.77, P<0.001) and not annual rainfall (r²=0.11, P=0.29). This result indicates that life‐form interactions have a significant role in controlling vegetation productivity across the rainfall gradient. The findings of this study emphasize the importance of considering heterogeneity rather than mean structure when modeling productivity, particularly when considering dynamic vegetation structure, where differences between landscape patches may not be well represented in the mean structure.     

Modeling the distribution and abundance of the non-native parasite, canine heartworm, in California coyotes

We applied a habitat-modeling approach using logistic regression to predict the distribution and abundance of canine heartworm ( Dirofilaria immitis ) in coyotes ( Canis latrans ) throughout California. Heartworm is an arthropod-borne parasite of considerable economic and ecological importance. In California, coyotes serve as the primary sylvatic maintenance host and represent a useful sentinel for this parasite. To develop the model, we used a large collection of coyote blood specimens and carcasses collected from spatially broad, yet nonrandom, locations in California. Survey data were useful in refining previous coarser models that predicted uniformly high prevalence of heartworm throughout the coastal and Sierra-Nevada foothills, by indicating variability within this broadly defined plant-climate zone. Due to the non-random nature and large spatial scale of our data-set, we restricted variables to those thought to be most generally important. Modeling indicated that woodlands with a relatively dense canopy, suitable breeding and host-seeking habitat of the western treehole mosquito ( Ochlerotatus sierrensis ), were a good predictor of heartworm prevalence. Within this habitat, prevalence increased with precipitation, which likely affected mosquito abundance. The distribution of heartworm was limited to areas with average cumulative temperatures high enough to enable larval development of heartworms within their mosquito vectors. The prediction accuracy of our model was supported by goodness-of-fit tests, cross-validation tests and external validation tests. The model provided a useful guide to the relative risk of heartworm exposure in California, although the resolution was necessarily coarse and prevalence estimates related to risk in an ordinal manner only.     

Spatial variability in the amount of forest litter at the local scale in northeastern China: Kriging and cokriging approaches to interpolation

Litter is essential to promote nutrient cycling and maintain the sustainability of forest resources. However, its variability has not been sufficiently studied at the local scale. The prediction of litter amount using ordinary cokriging with Pearson correlation analysis (COK_P) and ordinary cokriging with principal component analysis (COK_PCA) was compared with that using ordinary kriging (OK) based on cross‐validation at the local scale of a 1‐ha plot over natural spruce–fir mixed forest in Jilin Province, China. Litter samples in semidecomposed (F) and complete decomposed (H) horizons were collected using an equidistant grid point sampling of 10 m × 10 m. Pearson correlation analysis and principal component analysis (PCA) were used to confirm auxiliary variables. The results showed that the amount of litter was 19.65 t/ha in the F horizon and 10.37 t/ha in the H horizon. The spatial structure variance ratio in the H horizon was smaller than that in the F horizon, indicative of its stronger spatial autocorrelation. Spatial distributions of litter amount in both horizons exhibited a patchy and heterogeneous pattern. Of the selected stand characteristics and litter properties, litter moisture content indicated the strongest relationship with litter amount. Cross‐validation revealed that COK_PCA using the comprehensive score as an auxiliary variable produced the most accurate map. The average standard error and root‐mean‐square error between the predicted and measured values were always smaller, the mean error and mean standardized error were much closer to 0, and the root‐mean‐square standardized error was closer to 1 than COK_P using litter moisture and OK. Therefore, a clear advantage of cokriging based on principal component analysis was observed and COK_PCA was found to be a very useful approach for further interpolation prediction.     

Laboratory observations on the insusceptibility of raccoons to Dirofilaria immitis

Two raccoons, Procyon lotor, were exposed to Dirofilaria immitis by subcutaneous injection of infective third stage larvae obtained from experimentally-infected Aedes trivittatus. Nematodes were not recovered from either raccoon when examined at necropsy 223 and 254 days postexposure. Large numbers of adult D. immitis were found in six dogs used as controls. These data indicate that raccoons cannot support the development of D. immitis.