Confronting collinearity: comparing methods for disentangling the effects of habitat loss and fragmentation   总被引：1，自引：1，他引：0  

Adam C. Smith  Nicola Koper  Charles M. Francis  Lenore Fahrig 《Landscape Ecology》2009,24(10):1271-1285

Estimating the relative importance of habitat loss and fragmentation is necessary to estimate the potential benefits of specific management actions and to ensure that limited conservation resources are used efficiently. However, estimating relative effects is complicated because the two processes are highly correlated. Previous studies have used a wide variety of statistical methods to separate their effects and we speculated that the published results may have been influenced by the methods used. We used simulations to determine whether, under identical conditions, the following 7 methods generate different estimates of relative importance for realistically correlated landscape predictors: residual regression, model or variable selection, averaged coefficients from all supported models, summed Akaike weights, classical variance partitioning, hierarchical variance partitioning, and a multiple regression model with no adjustments for collinearity. We found that different methods generated different rankings of the predictors and that some metrics were strongly biased. Residual regression and variance partitioning were highly biased by correlations among predictors and the bias depended on the direction of a predictor’s effect (positive vs. negative). Our results suggest that many efforts to deal with the correlation between amount and fragmentation may have done more harm than good. If confounding effects are controlled and adequate thought is given to the ecological mechanisms behind modeled predictors, then standardized partial regression coefficients are unbiased estimates of the relative importance of amount and fragmentation, even when predictors are highly correlated.  相似文献   

Predicting the age of fish using general and generalized linear models of biometric data: A case study of two estuarine finfish from New South Wales, Australia     

Faith A. Ochwada  James P. Scandol  Charles A. Gray 《Fisheries Research》2008,90(1-3):187-197

Direct ageing of fish can be a laborious and expensive task when age estimates from a large population are required, and often involves a degree of subjectivity. This study examined the application of general and generalized linear models that predict the age of fish from a range of efficiently and objectively measured covariates. The data sampled were from yellowfin bream (Acanthopagrus australis (Sparidae) (Owen, 1853)) and sand whiting (Sillago ciliata (Sillaginidae) Cuvier, 1829) populations from New South Wales, Australia. The covariates evaluated in the models were fish length, otolith weight, sex and location (the estuary from which the fish were sampled). Akaike Information Criteria were used for model selection and residual plots of the final models revealed a satisfactory fit to the observations. The best fitting model for each species included all covariates. An additional investigation considered whether general and generalized linear models that predict age from two different categories of biometric information outperform age-length keys with respect to subsequent estimates of total mortality from catch-curve analysis. The two categories of biometric information differed in the ease and cost with which the information could be collected. The first category only included fish length and location as covariates, whilst the second category also included otolith weight and sex. It was found that traditional age-length keys outperformed the predictive models that estimated age from only fish length and location, because the results from the models were prone to significant bias. However, when otolith weight and sex were added as covariates to the predictive models, some of them, including a generalized linear model with a Poisson-distributed response variable, performed similarly to the age-length key. Given that otolith weight and the sex of fish are cheaper to quantify than age from a sectioned otolith in many situations, general or generalized linear models may represent a cheaper and faster method of estimating mortality compared to age-length keys. Such models can also easily incorporate the influence of spatial, temporal and demographic variation.  相似文献   

Determining resistance to <Emphasis Type="Italic">Fusarium verticillioides</Emphasis> and fumonisin accumulation in African maize inbred lines resistant to <Emphasis Type="Italic">Aspergillus flavus</Emphasis> and aflatoxins     

Lindy Joy Rose  Sheila Okoth  Ilze Beukes  Abigael Ouko  Marili Mouton  Bradley Charles Flett  Dan Makumbi  Altus Viljoen 《Euphytica》2017,213(4):93

Fusarium verticillioides and Aspergillus flavus cause Fusarium ear rot (FER) and Aspergillus ear rot (AER) of maize, respectively. Both pathogens are of concern to producers as they reduce grain yield and affect quality. F. verticillioides and A. flavus also contaminate maize grain with the mycotoxins fumonisins and aflatoxins, respectively, which has been associated with mycotoxicosis in humans and animals. The occurrence of common resistance mechanisms to FER and AER has been reported. Hence, ten Kenyan inbred lines resistant to AER and aflatoxin accumulation were evaluated for resistance to FER, F. verticillioides colonisation and fumonisin accumulation; and compared to nine South African lines resistant to FER and fumonisin accumulation. Field trials were conducted at three localities in South Africa and two localities in Kenya. FER severity was determined by visual assessment, while F. verticillioides colonisation and fumonisin content were quantified by real-time PCR and liquid chromatography tandem mass spectrometry, respectively. Significant genotype x environment interactions was determined at each location (P ≤ 0.05). Kenyan inbred CML495 was most resistant to FER and F. verticillioides colonisation, and accumulated the lowest concentration of fumonisins across localities. It was, however, not significantly more resistant than Kenyan lines CML264 and CKL05015, and the South African line RO549 W, which also exhibited low FER severity (≤5%), fungal target DNA (≤0.025 ng μL^?1) and fumonisin levels (≤2.5 mg kg^?1). Inbred lines resistant to AER and aflatoxin accumulation appear to be promising sources of resistance to F. verticillioides and fumonisin contamination.  相似文献   

Animal movement varies with resource availability,landscape configuration and body size: a conceptual model and empirical example     

Doherty  Tim S.  Fist  Charles N.  Driscoll  Don A. 《Landscape Ecology》2019,34(3):603-614

Landscape Ecology - Animals must move to find food, shelter and mates, and escape predation and competition. Changes in landscape configuration and resource availability can disrupt natural...  相似文献   

Encoding electronic properties by synthesis of axial modulation-doped silicon nanowires     

Yang C  Zhong Z  Lieber CM 《Science (New York, N.Y.)》2005,310(5752):1304-1307

We describe the successful synthesis of modulation-doped silicon nanowires by achieving pure axial elongation without radial overcoating during the growth process. Scanning gate microscopy shows that the key properties of the modulated structures-including the number, size, and period of the differentially doped regions-are defined in a controllable manner during synthesis, and moreover, that feature sizes to less than 50 nanometers are possible. Electronic devices fabricated with designed modulation-doped nanowire structures demonstrate their potential for lithography-independent address decoders and tunable, coupled quantum dots in which changes in electronic properties are encoded by synthesis rather than created by conventional lithography-based techniques.  相似文献   

绿豆抗豆象基因PCR标记的构建与应用   总被引：5，自引：1，他引：5  

程须珍  王素华  吴绍宇  周吉红  王述民  杨又迪 《中国农业科学》2005,38(8):1534-1539

 采用PCR分子标记技术，对16个绿豆品种（系）进行了遗传分析。在选用的56个随机引物中，发现抗豆象品种与感豆象品种间有一定差异。根据聚类分析结果将它们分成抗豆象野生种（TC1966）、抗豆象栽培种（V2709）、抗豆象杂交后代（VC3890A2/TC1966-23）和混合类型4个大组。以绿豆抗豆象和感豆象品种及抗豆象品种×感豆象品种组合的F2群体为试验材料，利用BSA法，对抗（感）豆象品种池和一个组合F2的抗（感）豆象池进行了鉴定，获得一个共显性标记。经F2分析，在抗豆象个体中扩增出约1.79 kb的特异片段或2个特异片段（1.79 kb/1.03 kb）；在感豆象个体中仅扩增出约1.03 kb的特异片段。初步认为此标记与TC1966的抗豆象基因位点紧密联锁，可用于绿豆抗豆象种质鉴定和遗传育种的分子标记辅助选择。  相似文献   

Genome‐wide markers reveal temporal instability of local population genetic structure in the cotton fleahopper,Pseudatomoscelis seriatus (Hemiptera: Miridae)     

Tyler J Raszick  Charles P‐C Suh  Charles Michael Dickens  Gregory A Sword 《Pest management science》2020,76(1):324-332

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The effectiveness of consistent roguing in managing banana bunchy top disease in smallholder production in Africa     

Bonaventure A. Omondi  Misheck M. Soko  Innocent Nduwimana  Ronald T. Delano  Celestin Niyongere  Alice Simbare  Donald Kachigamba  Charles Staver 《Plant pathology》2020,69(9):1754-1766

The removal of infected individuals is a common practice in the management of plant disease outbreaks. It minimizes the contact between healthy individuals and inoculum sources by reducing the infectious window of contaminated individuals. This requires early detection and consistent removal at landscape scale. Roguing of mats with symptoms of banana bunchy top disease (BBTD) in Cavendish banana production systems has been tested in Australia, using trained personnel, but has never been tested in smallholder systems. We studied the effectiveness of long-term consistent roguing in prolonging the productivity of banana orchards under smallholder farming systems in highland banana and plantain dominated production systems in Africa. We assessed the possibility of low-risk seed sourcing from the managed plots. Roguing reduced BBTD incidence to 2% in managed farmer fields and to 10% in experimental field plots, while a nonmanaged field eventually collapsed in the same period. With roguing, new infections decreased monthly compared to an exponential increase in a nonmanaged field. The emergence of new infections in both managed and nonmanaged farms followed a seasonal cycle. BBTD managed plots were a source of low-risk seed for replacing the rogued mats in the same fields, but perhaps not safe for use in nonendemic areas. We conclude that it is possible for smallholder farmers to recover and maintain banana productivity with rigorous roguing, which would entail early identification of symptoms and early removal of diseased mats. Studies are needed on the intensity of roguing under different disease and production conditions.  相似文献   

The potential of mini-ridging for controlling intrarow weeds: estimating minimum lethal burial depth     

Charles N. Merfield  Jacquelyn R. Bennett  Nadine A. Berry  Arthur Bluon  Dean M. O’Connell  Simon Hodge 《Weed Research》2020,60(5):353-362

Weed management using synthetic herbicides is undergoing a global decline, necessitating a re-evaluation of existing control measures and the development of novel weed management tools. ‘Mini-ridging’ is a non-discriminatory, physical weeding method that functions by burying weeds in the intrarow with a laterally shifted ridge of soil. In glasshouse trials using potted plants, we found that plant recovery after soil application was influenced by plant size, which in turn was influenced by plant species, developmental stage and/or age. The likelihood of plant recovery after soil application was negatively related to the depth of soil applied: very few plants survived total coverage by soil but, conversely, survival could be substantial if some parts of the plants were not covered. The results suggest that burial under a depth of 6 cm of soil would eliminate most plants regardless of species or growth stage. Larger plants would require the application of a greater total depth of soil to achieve this 6 cm of soil cover, and weed management would, therefore, tend to be more successful and more practical if weeds were targeted when still small. This research demonstrates the potential of plant burial as a simple and reliable means of non-chemical weed management, and re-emphasises that, for weed control to be effective, the applied soil layer must cover the whole plant.  相似文献   

Planktonic foraminifera of the California Current reflect 20th-century warming     

Field DB  Baumgartner TR  Charles CD  Ferreira-Bartrina V  Ohman MD 《Science (New York, N.Y.)》2006,311(5757):63-66

It is currently unclear whether observed pelagic ecosystem responses to ocean warming, such as a mid-1970s change in the eastern North Pacific, depart from typical ocean variability. We report variations in planktonic foraminifera from varved sediments off southern California spanning the past 1400 years. Increasing abundances of tropical/subtropical species throughout the 20th century reflect a warming trend superimposed on decadal-scale fluctuations. Decreasing abundances of temperate/subpolar species in the late 20th century indicate a deep, penetrative warming not observed in previous centuries. These results imply that 20th-century warming, apparently anthropogenic, has already affected lower trophic levels of the California Current.  相似文献