Multiscale sources of variation in ecological variables: modeling spatial dispersion,elaborating sampling designs

Detection of structured spatial variation and identification of spatial scales are important aspects of ecological studies. Spatial structures can correspond to physical features of the environment or to intrinsic characteristics of ecological processes and phenomena. Spatial variability has been approached through several techniques such as classical analysis of variance, or the calculation of fractal dimensions, correlograms or variograms. Under certain assumptions, these techniques are all closely related to one another and represent equivalent tools to characterize spatial structures.Our perception of ecological variables and processes depends on the scale at which variables are measured. We propose simple nested sampling designs enabling the detection of a wide range of spatial structures that show the relationships among nested spatial scales. When it is known that the phenomenon under study is structured as a nested series of spatial scales, this provides useful information to estimate suitable sampling intervals, which are essential to establish the relationships between spatial patterns and ecological phenomena. The use of nested sampling designs helps in choosing the most suitable solutions to reduce the amount of random variation resulting from a survey. These designs are obtained by increasing the sampling intensity to detect a wider spectrum of frequencies, or by revisiting the sampling technique to select more representative sampling units.     

Diversity of Virulence in Phytophthora parasitica on Tobacco, as Reflected by Nuclear RFLPs

ABSTRACT A worldwide collection of P. parasitica isolates was investigated for the ability to infect tobacco and tomato, as related to elicitin production. Elicitin was produced by all nontobacco isolates, and nonproducing strains all were isolated from tobacco. In addition, producing strains were isolated from tobacco and coexisted with nonproducing (TE ) strains. Elicitin production generally was associated with low virulence on tobacco and frequent pathogenicity on tomato, whereas TE isolates generally were highly virulent and specialized to tobacco. Analysis of both mitochondrial and nuclear DNA restriction fragment length polymorphisms indicated, for the first time, that black shank isolates can be distinguished from other P. parasitica isolates on the basis of genetic criteria. Our results suggest that severe black shank is caused by a limited number of TE strains that have been disseminated by clonal evolution. Mutations in the TE phenotype seem to have arisen independently in several genetic backgrounds and distinct geographic areas. The fortuitous absence of elicitin production has precluded population replacements in areas of intensive tobacco cultivation. Thus, monitoring the loss of elicitin production in developing tobacco areas should be considered in disease management.     

Inheritance and Mechanisms of Resistance to Tebuconazole, a Sterol C14-Demethylation Inhibitor, inNectria haematococca

Genetic control and mechanisms of resistance to tebuconazole, a sterol C14-demethylation inhibitor, were investigated in the phytopathogenic fungusNectria haematococca. Resistant mutants have been selected from the laboratory, following UV irradiation. They have been characterized through genetic crosses and mutations in at least three genes were found to be responsible for resistance. The genesTeb1, Teb2, andTeb3were clearly identified, a fourth gene calledTeb4could be hypothesized. Mutations at lociTeb2andTeb3induced pleiotropic effects such as reduced sporulation and growth rate, mycelium pigmentation (Teb2), or altered ascospore viability (Teb3). The resistance levels determined by mutations in the different genes were relatively low (below 10). When associated in double mutants, the additive effect was recorded. Cross-resistance toward other sterol C14-demethylation inhibitors was observed in all the resistant strains, except in theTeb4-carrying strain; moreover, for some C14-demethylation inhibitors hypersensitivity was expressed. A constitutive energy-dependent efflux seemed implicated in the mechanism of resistance for theTeb1-carrying strain and probably also for theTeb2andTeb3-carrying strains. However, theTeb4-carrying strain exhibited a kinetic of fungicide uptake similar to that of the wild-type strain. The sterol profile of theTeb4-carrying strain was similar to that of all the other resistant mutants and wild-type strains. Thus the resistance mechanism induced by mutation at theTeb4locus has not been found yet.     

Continuous and non-invasive study of brain oxygenation in the calf by near infrared spectroscopy

Near infrared spectroscopy (NIBS) was used to detect changes in brain oxygenation in five tranquilised calves that were placed on a hypoxic gas mixture (10 per cent O₂/90 per cent N₂) and hyperoxic gas mixture (30 per cent O₂/70 per cent N₂) for five minutes at each concentration. A NIRO 500 (Hamamatsu, Japan) was used for the NIBS, with the incident light source and separate detector (optodes) placed on shaved skin on the most dorsal surface of the frontal bone. Sequential arterial blood gas sample analyses provided confirmation of the appropriate change in systemic oxygenation status. By the end of the five-minute-period of breathing 10 per cent oxygen, NIBS of the calf head detected highly significant changes in haemoglobin oxygenation reflective of hypoxaemia, with oxyhaemoglobin decreasing by 23·5 units (P<0·01) and deoxyhaemoglobin increasing by 45·6 units, (P<0·01) from the baseline of breathing room air. Total haemoglobin (oxyhaemoglobin + deoxyhaemoglobin) showed a significant increase of 22·1 units (P<0·05) but there was no significant change in LAIRS determined cytochrome aa₃ oxygenation. Concomitant blood gas alterations included significant decreases in Pa)₂ (−27·8 mmHg, P<0·01), haemoglobin saturation (−29·0 per cent, P<0·05), and PaCO₂ (−7·8 mmHg, P<0·05) and significantly increased blood pH (0·059, P<0·05). At the end of the five minutes of breathing 30 per cent oxygen NIBS of the calf head detected significantly increased oxyhaemoglobin (13·1 units, P<0·01) and decreased deoxyhaemoglobin (−13·7 units, P<0·05) when compared with baseline breathing of room aim. Total haemoglobin and cytochrome aa₃ were unchanged from baseline. The accompanying arterial blood gas changes included significant increases in PaO₂ (30·9 mmHg, P<0·05), arterial O₂ saturation (11·7 per cent, P<0·05), and significantly decreased pH (−0·026, P<0·05), This study showed that NIRS can be used to continuously and non-invasively detect cerebral oxygenation changes in the live calf in response to both increased and decreased systemic arterial oxygen. Additionally, despite induction of profound hypoxaemia, cytochrome aa₃ in the brain did not appear to become reduced.     

Statistical models of landscape pattern metrics,with applications to regional scale dynamic forest simulations

Forest managers in Canada need to model landscape pattern or spatial configurationoverlarge (100,000 km²) regions. This presents a scalingproblem, as landscape configuration is measured at a high spatial resolution,but a low spatial resolution is indicated for regional simulation. We present astatistical solution to this scaling problem by showing how a wide range oflandscape pattern metrics can be modelled from low resolution data. Our studyarea comprises about 75,000 km² of boreal mixedwoodforest in northeast Alberta, Canada. Within this area we gridded a sample of 84digital forest cover maps, each about 9500 ha in size, to aresolution of 1 ha and used FRAGSTATS to compute a suite oflandscape pattern metrics for each map. We then used multivariate dimensionreduction techniques and canonical correlation analysis to model therelationship between landscape pattern metrics and simpler stand table metricsthat are easily obtained from non-spatial forest inventories. These analyseswere performed on four habitat types common in boreal mixedwood forests: youngdeciduous, old deciduous, white spruce, and mixedwood types. Using only threelandscape variables obtained directly from stand attribute tables (totalhabitatarea, and the mean and standard deviation of habitat patch size), ourstatistical models explained more than 73% of the joint variation in fivelandscape pattern metrics (representing patch shape, forest interior habitat,and patch isolation). By PCA, these five indices captured much of the totalvariability in the rich set of landscape pattern metrics that FRAGSTATS cangenerate. The predictor variables and strengths of association were highlyconsistent across habitat classes. We illustrate the potential use of suchstatistical relationships by simulating the regional, cumulative effects ofwildfire and forest management on the spatial arrangement of forest patches,using non-spatial stand attribute tables.This revised version was published online in May 2005 with corrections to the Cover Date.     

Keratoprosthesis with retrocorneal fixation: preliminary results in dogs with corneal blindness

Objective To evaluate the use and complications of a penetrating keratoprosthesis implantation in the management of corneal opacification in dogs. Methods A retrospective clinical study describes the indications for the surgical technique utilized and the outcomes of this procedure in 20 eyes of 19 dogs with blindness of corneal origin. A successful surgical outcome was defined as a clear keratoprosthesis optic and improvement or restoration of functional vision over a follow‐up period ranging from at least 8 months to a maximum of 7 years. Results Eyes with total corneal opacification resulting from chronic superficial keratitis (n = 11), keratoconjunctivitis sicca (n = 5), endothelial dystrophy (n = 3) and chemical burn (n = 1) were treated by unilateral (n = 18) or bilateral (n = 1) full‐thickness implantation of a keratoprosthesis. Keratoprostheses were retained in 15 eyes (75%) which regained vision to the date of reporting. Among these eyes, six had uncomplicated postoperative course, five developed retroprosthetic membranes and four developed granulation tissue over the optic of the keratoprostheses. These complications were successfully removed surgically in the nine eyes. The five remaining eyes (25%) developed serious early postoperative complications, for which enucleation had to be performed. Conclusion In keratopathies in which the corneal opacification could not be treated by standard medical or surgical procedures, this keratoprosthesis appears to be promising to restore vision in chronic superficial keratitis and deep corneal dystrophy. It appears to have a poor prognosis in keratoconjunctivitis sicca in brachycephalic dogs. The post operative complications retro‐prosthetic membranes and granulomatous overgrowth could be treated well.     

One century of eel growth: changes and implications

Abstract – A cooperative effort gathered a large European length‐at‐age data set (N = 45,759, Lat. 36S–61N Long. 10W–27E) for Anguilla anguilla, covering one century. To assess the effect of global warming during the last century and habitat effects on growth, a model was fitted on the data representing the conditions met at the distribution area scale. Two GLMs were designed to predict eel log(GR): one model was fitted to the whole data and the other was fitted to the female data subset. A model selection procedure was applied to select the best predictors among sex, age class, five temperature parameters and six habitat parameters (depth, salinity and four variables related to the position in the catchment). The yearly sum of temperatures above 13 °C (TempSUP13), the relative distance within the catchment, sex, age class, salinity class and depth class were finally selected. The best model predicted eel log(GR) with a 64.46% accuracy for the whole data and 66.91% for the female eel data. Growth rate (GR) was greater in habitats close to the sea and in deep habitats. TempSUP13 variable had one of the greatest predictive powers in the model, showing that global warming had affected eel growth during the last century.