Pierre Legendre - Profile on Academia.edu (original) (raw)
Papers by Pierre Legendre
99mTc labeled red blood cells versus ?-phlebography in diagnosis of deep vein thrombosis
European Journal of Nuclear Medicine, 1982
The diagnosis of deep veto thrombosis (DVT) using blood pool scanning with in vivo labeled red ce... more The diagnosis of deep veto thrombosis (DVT) using blood pool scanning with in vivo labeled red cells has been described by Beswick et al. [1], and more recently by Kempi and Van Der Linden [4]. This technique is especially useful for cardiac imaging, but we do not entirely agree that it is adequate when used to study veins. A non specific clot tracer can identify DVT from Indirect evidence such as absence of major vessels and/or collateral routes. This labehng method can be compared with ),-phlebography, in which the diagnostic criteria are similar, although the route of administration is different. We have compared the two methods in various patients suffering from thromboembolic disease [2]. In vivo labeling of red blood cells depends on detection at equilibrium, the 99mTc being equally distributed. However, capillary radioactivity produces extra background radioactivity which distorts the imaging contrast. The 7-camera resolution makes the identification of major deep veins from their homologous arteries, which are detected at the same time, difficult. This difficulty in resolution does not exist for superficial veins, but their study is less interesting: the post-phlebitic varicose veins cannot be diagnosed by this means only and superficial vein thrombosis is clinically evident; their migration power is low but they may be associated with DVT. On the other hand, 7-phlebography records the first transit of a 99mTc-compound injected into a dorsal vein of a foot or hand, according to the territory studied. Only the venous system appears, which makes it possible to spot the extension of DVT and the dynamic value of collateral circulation. Besides, the
Vegan: Community Ecology Package
R package …, 2007
... Published: 2010-03-08. Author: Jari Oksanen, F. Guillaume Blanchet, Roeland Kindt, Pierre Leg... more ... Published: 2010-03-08. Author: Jari Oksanen, F. Guillaume Blanchet, Roeland Kindt, Pierre Legendre, RB O'Hara, Gavin L. Simpson, Peter Solymos, M. Henry H. Stevens, Helene Wagner. Maintainer: Jari Oksanen <jari.oksanen at oulu.fi>. License: GPL-2. ...
Journal of Classification
De Soete (1986, 1988) proposed some years ago a method for optimal variable weighting for ultrame... more De Soete (1986, 1988) proposed some years ago a method for optimal variable weighting for ultrametric and additive tree fitting. This paper extends De Soete's method to optimal variable weighting for K-means partitioning. We also describe some new features and improvements to the algorithm proposed by De Soete. Monte Carlo simulations have been conducted using different error conditions. In all cases (i.e., ultrametric or additive trees, or Kmeans partitioning), the simulation results indicate that the optimal weighting procedure should be used for analyzing data containing noisy variables that do not contribute relevant information to the classification structure. However, if the data involve error-perturbed variables that are relevant to the classification or outliers, it seems better to cluster or partition the entities by using variables with equal weights. A new computer program, OVW, which is available to researchers as freeware, implements improved algorithms for optimal variable weighting for ultrametric and additive tree clustering, and includes a new algorithm for optimal variable weighting for K-means partitioning. .
Community structure of Neotropical wetland insects in Northern Venezuela. I. Temporal and environmental factors app: 1
Fundamental and Applied Limnology
An Appropriate Space for Clustering Selected Groups of Western North American Salmo
Systematic Zoology
Interpreting the replacement and richness difference components of beta diversity
Global Ecology and Biogeography
Human and natural controls of the variation in aboveground tree biomass in African dry tropical forests
Ecological applications : a publication of the Ecological Society of America, Jan 4, 2017
Understanding the anthropogenic and natural controls that affect the patterns, distribution and d... more Understanding the anthropogenic and natural controls that affect the patterns, distribution and dynamics of terrestrial carbon is crucial to meeting climate change mitigation objectives. We assessed the human and natural controls over aboveground tree biomass density in African dry tropical forests, using Zambia's first nation-wide forest inventory. We identified predictors that best explain the variation in biomass density, contrasted anthropogenic and natural sites at different spatial scales and compared sites with different stand structure characteristics and species composition. In addition, we evaluated the effects of different management and conservation practices on biomass density. Variation in biomass density was mostly determined by biotic processes, linked with both species richness and dominance (evenness) and, to a lesser extent, by land use, environmental controls, and spatial structure. Biomass density was negatively associated with tree species evenness and posi...
Proceedings. Biological sciences, Jan 12, 2017
Ocean tides and winter surface storms are among the main factors driving the dynamics and spatial... more Ocean tides and winter surface storms are among the main factors driving the dynamics and spatial structure of marine coastal species, but the understanding of their impact on deep-sea and hydrothermal vent communities is still limited. Multidisciplinary deep-sea observatories offer an essential tool to study behavioural rhythms and interactions between hydrothermal community dynamics and environmental fluctuations. Here, we investigated whether species associated with a Ridgeia piscesae tubeworm vent assemblage respond to local ocean dynamics. By tracking variations in vent macrofaunal abundance at different temporal scales, we provide the first evidence that tides and winter surface storms influence the distribution patterns of mobile and non-symbiotic hydrothermal species (i.e. pycnogonids Sericosura sp. and Polynoidae polychaetes) at more than 2 km depth. Local ocean dynamics affected the mixing between hydrothermal fluid inputs and surrounding seawater, modifying the environmen...
Frontiers in Microbiology, 2016
The interaction between plants and microorganisms, which is the driving force behind the decontam... more The interaction between plants and microorganisms, which is the driving force behind the decontamination of petroleum hydrocarbon (PHC) contamination in phytoremediation technology, is poorly understood. Here, we aimed at characterizing the variations between plant compartments in the microbiome of two willow cultivars growing in contaminated soils. A field experiment was setup at a former petrochemical plant in Canada and after two growing seasons, bulk soil, rhizosphere soil, roots, and stems samples of two willow cultivars (Salix purpurea cv. FishCreek, and Salix miyabeana cv. SX67) growing at three PHC contamination concentrations were taken. DNA was extracted and bacterial 16S rRNA gene and fungal internal transcribed spacer (ITS) regions were amplified and sequenced using an Ion Torrent Personal Genome Machine (PGM). Following multivariate statistical analyses, the level of PHC-contamination appeared as the primary factor influencing the willow microbiome with compartment-specific effects, with significant differences between the responses of bacterial, and fungal communities. Increasing PHC contamination levels resulted in shifts in the microbiome composition, favoring putative hydrocarbon degraders, and microorganisms previously reported as associated with plant health. These shifts were less drastic in the rhizosphere, root, and stem tissues as compared to bulk soil, probably because the willows provided a more controlled environment, and thus, protected microbial communities against increasing contamination levels. Insights from this study will help to devise optimal plant microbiomes for increasing the efficiency of phytoremediation technology.
Inventaire a�rien de la faune dans le Moyen Nord qu�b�cois
Can J Zool, 1978
Clustering and Partitioning
Developments in Paleoenvironmental Research, 2012
From Classical to Canonical Ordination
Developments in Paleoenvironmental Research, 2012
Page 1. Chapter 8 From Classical to Canonical Ordination Pierre Legendre and H. John B. Birks Abs... more Page 1. Chapter 8 From Classical to Canonical Ordination Pierre Legendre and H. John B. Birks Abstract The simple or classical ordination methods mostly used by palaeo-ecologists and palaeolimnologists are principal component ...
Assessing the scale-specific importance of niches and other spatial processes on beta diversity : a case study from a temperate forest
Oecologia, 2009
Niche processes and other spatial processes, such as dispersal, may simultaneously control beta d... more Niche processes and other spatial processes, such as dispersal, may simultaneously control beta diversity, yet their relative importance may shift across spatial and temporal scales. Although disentangling the relative importance of these processes has been a continuing methodological challenge, recent developments in multi-scale spatial and temporal modeling can now help ecologists estimate their scale-specific contributions. Here we present a statistical approach to (1) detect the presence of a space-time interaction on community composition and (2) estimate the scale-specific importance of environmental and spatial factors on beta diversity. To illustrate the applicability of this approach, we use a case study from a temperate forest understory where tree seedling abundances were monitored during a 9-year period at 40 permanent plots. We found no significant space-time interaction on tree seedling composition, which means that the spatial abundance patterns did not vary over the study period. However, for a given year the relative importance of niche processes and other spatial processes was found to be scale-specific. Tree seedling abundances were primarily controlled by a broad-scale environmental gradient, but within the confines of this gradient the finer scale patchiness was largely due to other spatial processes. This case study illustrates that these two sets of processes are not mutually exclusive and can affect abundance patterns in a scale-dependent manner. More importantly, the use of our methodology for future empirical studies should help in the merging of niche and neutral perspectives on beta diversity, an obvious next step for community ecology.
Hydrobiologia, 1982
A study of the freshwater gastropods in the Saint Lawrence river near Montreal was undertaken to ... more A study of the freshwater gastropods in the Saint Lawrence river near Montreal was undertaken to characterize the populations living in the benthos and on the vegetation, and to define the effects of a deterioration of water quality. Ninety-eight samples, collected simultaneously from the benthos and on macrophytes, were expressed as the logarithm of each species' relative abundance. WPGMA clustering, principal coordinates and discriminant analysis were used to describe and characterize differences between samples. Diversity was also computed to show the transformations of population structure due to differences in pollution levels. Prosobranch snails predominated in benthic populations while pulmonates characterized vegetation. A decrease in the number of species was the characteristic response to increasing pollution levels upon both types of substrates. High hydrocarbon levels were related to a decrease in the diversity of snail populations on the vegetation only. Predominance of prosobranchs in the benthos and pulmonates on the vegetation could be explained by a differential dependence of those two groups of snails on the aquatic medium, and by considering modes of nutrition. Sporadic oil spills affected the snail populations living on macrophytes .
A Comparison of Sampling Methods to Estimate Production Metrics of Littoral Zone Fish Based on Multi-Spatial Habitat Variables of a Manitoba Reservoir
ABSTRACT
Spatial modelling: a comprehensive framework for principal coordinate analysis of neighbour matrices (PCNM)
Ecological Modelling, Jul 1, 2006
... It can be constructed using distance criteria (select a distance threshold and connect all po... more ... It can be constructed using distance criteria (select a distance threshold and connect all points that are within that distance of each other), or more sophisticated procedures such as the Delaunay triangulation, Gabriel graph, relative neighbourhood graph, sphere of influence, or ...
Evolution and Determinants
Journal of Classification, Apr 1, 2009
We would like to thank the members of the LEMEE (Laboratoire d'Écologie Moléculaire et d'Évolutio... more We would like to thank the members of the LEMEE (Laboratoire d'Écologie Moléculaire et d'Évolution) of Université de Montréal for their constructive comments on a preliminary version of this manuscript as well as three anonymous reviewers. This study was supported by NSERC and FQRNT scholarships to VC and by NSERC grants OGP0007738 to PL and OGP0155251 to FJL.
Journal of Phycology, Sep 1, 1987
Thii paper ei'nluates ihe utilisation of space hy epihenthic diatom cells, as a responsf to emnro... more Thii paper ei'nluates ihe utilisation of space hy epihenthic diatom cells, as a responsf to emnronmeutal varia' tions. The aggregation pattern of fife species of epihenthic diatoms was quantified nnd compared to prm'ide evidenrf for thr significance of cell motility as an adaptive mechanismfor space occupation and monopoly. The epibenthic diatoms included (1) non-mobile colonial species forming either fan-shaped fSyncdra tabulata (Ag.) Kz.) or arborescent (Gomphonema kamtschaticum var. californicum Grun.) colonies: (2) stou-'mm-itig f'Cocconeis costata Greg, and Amphora pusioC/j, and (3)fast-moving fNaviculadirectaAV. Sm.)Ra.) non-colonialspeaes. The aggregation pattern of S. tabulata did not vary significantly among stx different light intensities manipulated in nature. The major patterns of aggregation were identified using analyiis of cmariance and dummy-variable regresiion. Highly mobile N. directa are significantly Ifsŝ gg^^g*tt^d fhan the four other diatom species. Son-mobile and s^lou'-moi'ing species show a similar, highly aggregated pattern. The occurrence of two patterns of spatial dispersion indicates that growth forms hear far-ranging ecological implications uith retpect to colonization .strategies, immigration, and possibly impact by grazers. An integrated model of grmith form characteristics, biological properties, and ecological implications is presented for epihenthic diatoms.
Environ Earth Sci, 2000
This paper describes a geostatistical technique based on conditional simulations to assess confid... more This paper describes a geostatistical technique based on conditional simulations to assess confidence intervals of local estimates of lake pH values on the Canadian Shield. This geostatistical approach has been developed to deal with the estimation of phenomena with a spatial autocorrelation structure among observations. It uses the autocorrelation structure to derive minimum-variance unbiased estimates for points that have not been measured, or to estimate average values for new surfaces. A survey for lake water chemistry has been conducted by the Ministère de l'Environnement du Québec between 1986 and 1990, to assess surface water quality and delineate the areas affected by acid precipitation on the southern Canadian Shield in Québec. The spatial structure of lake pH was modeled using two nested spherical variogram models, with ranges of 20 km and 250 km, accounting respectively for 20% and 55% of the spatial variation, plus a random component accounting for 25%. The pH data have been used to construct a number of geostatistical simulations that produce plausible realizations of a given random function model, while 'honoring' the experimental values (i.e., the real data points are among the simulated data), and that correspond to the same underlying variogram model. Post-processing of a large number of these simulations, that are equally likely to occur, enables the estimation of mean pH values, the proportion of affected lakes (lakes with pH^5.5), and the potential error of these parameters within small regions (100 km!100 km). The method provides a procedure to establish whether acid rain control programs will succeed in reducing acidity in surface waters, allowing one to consider small areas with particular physiographic features rather than large drainage basins with several sources of heterogeneity. This judgment on the reduction of surface water acidity will be possible only if the amount of uncertainty in the estimation of mean pH is properly quantified.
99mTc labeled red blood cells versus ?-phlebography in diagnosis of deep vein thrombosis
European Journal of Nuclear Medicine, 1982
The diagnosis of deep veto thrombosis (DVT) using blood pool scanning with in vivo labeled red ce... more The diagnosis of deep veto thrombosis (DVT) using blood pool scanning with in vivo labeled red cells has been described by Beswick et al. [1], and more recently by Kempi and Van Der Linden [4]. This technique is especially useful for cardiac imaging, but we do not entirely agree that it is adequate when used to study veins. A non specific clot tracer can identify DVT from Indirect evidence such as absence of major vessels and/or collateral routes. This labehng method can be compared with ),-phlebography, in which the diagnostic criteria are similar, although the route of administration is different. We have compared the two methods in various patients suffering from thromboembolic disease [2]. In vivo labeling of red blood cells depends on detection at equilibrium, the 99mTc being equally distributed. However, capillary radioactivity produces extra background radioactivity which distorts the imaging contrast. The 7-camera resolution makes the identification of major deep veins from their homologous arteries, which are detected at the same time, difficult. This difficulty in resolution does not exist for superficial veins, but their study is less interesting: the post-phlebitic varicose veins cannot be diagnosed by this means only and superficial vein thrombosis is clinically evident; their migration power is low but they may be associated with DVT. On the other hand, 7-phlebography records the first transit of a 99mTc-compound injected into a dorsal vein of a foot or hand, according to the territory studied. Only the venous system appears, which makes it possible to spot the extension of DVT and the dynamic value of collateral circulation. Besides, the
Vegan: Community Ecology Package
R package …, 2007
... Published: 2010-03-08. Author: Jari Oksanen, F. Guillaume Blanchet, Roeland Kindt, Pierre Leg... more ... Published: 2010-03-08. Author: Jari Oksanen, F. Guillaume Blanchet, Roeland Kindt, Pierre Legendre, RB O'Hara, Gavin L. Simpson, Peter Solymos, M. Henry H. Stevens, Helene Wagner. Maintainer: Jari Oksanen <jari.oksanen at oulu.fi>. License: GPL-2. ...
Journal of Classification
De Soete (1986, 1988) proposed some years ago a method for optimal variable weighting for ultrame... more De Soete (1986, 1988) proposed some years ago a method for optimal variable weighting for ultrametric and additive tree fitting. This paper extends De Soete's method to optimal variable weighting for K-means partitioning. We also describe some new features and improvements to the algorithm proposed by De Soete. Monte Carlo simulations have been conducted using different error conditions. In all cases (i.e., ultrametric or additive trees, or Kmeans partitioning), the simulation results indicate that the optimal weighting procedure should be used for analyzing data containing noisy variables that do not contribute relevant information to the classification structure. However, if the data involve error-perturbed variables that are relevant to the classification or outliers, it seems better to cluster or partition the entities by using variables with equal weights. A new computer program, OVW, which is available to researchers as freeware, implements improved algorithms for optimal variable weighting for ultrametric and additive tree clustering, and includes a new algorithm for optimal variable weighting for K-means partitioning. .
Community structure of Neotropical wetland insects in Northern Venezuela. I. Temporal and environmental factors app: 1
Fundamental and Applied Limnology
An Appropriate Space for Clustering Selected Groups of Western North American Salmo
Systematic Zoology
Interpreting the replacement and richness difference components of beta diversity
Global Ecology and Biogeography
Human and natural controls of the variation in aboveground tree biomass in African dry tropical forests
Ecological applications : a publication of the Ecological Society of America, Jan 4, 2017
Understanding the anthropogenic and natural controls that affect the patterns, distribution and d... more Understanding the anthropogenic and natural controls that affect the patterns, distribution and dynamics of terrestrial carbon is crucial to meeting climate change mitigation objectives. We assessed the human and natural controls over aboveground tree biomass density in African dry tropical forests, using Zambia's first nation-wide forest inventory. We identified predictors that best explain the variation in biomass density, contrasted anthropogenic and natural sites at different spatial scales and compared sites with different stand structure characteristics and species composition. In addition, we evaluated the effects of different management and conservation practices on biomass density. Variation in biomass density was mostly determined by biotic processes, linked with both species richness and dominance (evenness) and, to a lesser extent, by land use, environmental controls, and spatial structure. Biomass density was negatively associated with tree species evenness and posi...
Proceedings. Biological sciences, Jan 12, 2017
Ocean tides and winter surface storms are among the main factors driving the dynamics and spatial... more Ocean tides and winter surface storms are among the main factors driving the dynamics and spatial structure of marine coastal species, but the understanding of their impact on deep-sea and hydrothermal vent communities is still limited. Multidisciplinary deep-sea observatories offer an essential tool to study behavioural rhythms and interactions between hydrothermal community dynamics and environmental fluctuations. Here, we investigated whether species associated with a Ridgeia piscesae tubeworm vent assemblage respond to local ocean dynamics. By tracking variations in vent macrofaunal abundance at different temporal scales, we provide the first evidence that tides and winter surface storms influence the distribution patterns of mobile and non-symbiotic hydrothermal species (i.e. pycnogonids Sericosura sp. and Polynoidae polychaetes) at more than 2 km depth. Local ocean dynamics affected the mixing between hydrothermal fluid inputs and surrounding seawater, modifying the environmen...
Frontiers in Microbiology, 2016
The interaction between plants and microorganisms, which is the driving force behind the decontam... more The interaction between plants and microorganisms, which is the driving force behind the decontamination of petroleum hydrocarbon (PHC) contamination in phytoremediation technology, is poorly understood. Here, we aimed at characterizing the variations between plant compartments in the microbiome of two willow cultivars growing in contaminated soils. A field experiment was setup at a former petrochemical plant in Canada and after two growing seasons, bulk soil, rhizosphere soil, roots, and stems samples of two willow cultivars (Salix purpurea cv. FishCreek, and Salix miyabeana cv. SX67) growing at three PHC contamination concentrations were taken. DNA was extracted and bacterial 16S rRNA gene and fungal internal transcribed spacer (ITS) regions were amplified and sequenced using an Ion Torrent Personal Genome Machine (PGM). Following multivariate statistical analyses, the level of PHC-contamination appeared as the primary factor influencing the willow microbiome with compartment-specific effects, with significant differences between the responses of bacterial, and fungal communities. Increasing PHC contamination levels resulted in shifts in the microbiome composition, favoring putative hydrocarbon degraders, and microorganisms previously reported as associated with plant health. These shifts were less drastic in the rhizosphere, root, and stem tissues as compared to bulk soil, probably because the willows provided a more controlled environment, and thus, protected microbial communities against increasing contamination levels. Insights from this study will help to devise optimal plant microbiomes for increasing the efficiency of phytoremediation technology.
Inventaire a�rien de la faune dans le Moyen Nord qu�b�cois
Can J Zool, 1978
Clustering and Partitioning
Developments in Paleoenvironmental Research, 2012
From Classical to Canonical Ordination
Developments in Paleoenvironmental Research, 2012
Page 1. Chapter 8 From Classical to Canonical Ordination Pierre Legendre and H. John B. Birks Abs... more Page 1. Chapter 8 From Classical to Canonical Ordination Pierre Legendre and H. John B. Birks Abstract The simple or classical ordination methods mostly used by palaeo-ecologists and palaeolimnologists are principal component ...
Assessing the scale-specific importance of niches and other spatial processes on beta diversity : a case study from a temperate forest
Oecologia, 2009
Niche processes and other spatial processes, such as dispersal, may simultaneously control beta d... more Niche processes and other spatial processes, such as dispersal, may simultaneously control beta diversity, yet their relative importance may shift across spatial and temporal scales. Although disentangling the relative importance of these processes has been a continuing methodological challenge, recent developments in multi-scale spatial and temporal modeling can now help ecologists estimate their scale-specific contributions. Here we present a statistical approach to (1) detect the presence of a space-time interaction on community composition and (2) estimate the scale-specific importance of environmental and spatial factors on beta diversity. To illustrate the applicability of this approach, we use a case study from a temperate forest understory where tree seedling abundances were monitored during a 9-year period at 40 permanent plots. We found no significant space-time interaction on tree seedling composition, which means that the spatial abundance patterns did not vary over the study period. However, for a given year the relative importance of niche processes and other spatial processes was found to be scale-specific. Tree seedling abundances were primarily controlled by a broad-scale environmental gradient, but within the confines of this gradient the finer scale patchiness was largely due to other spatial processes. This case study illustrates that these two sets of processes are not mutually exclusive and can affect abundance patterns in a scale-dependent manner. More importantly, the use of our methodology for future empirical studies should help in the merging of niche and neutral perspectives on beta diversity, an obvious next step for community ecology.
Hydrobiologia, 1982
A study of the freshwater gastropods in the Saint Lawrence river near Montreal was undertaken to ... more A study of the freshwater gastropods in the Saint Lawrence river near Montreal was undertaken to characterize the populations living in the benthos and on the vegetation, and to define the effects of a deterioration of water quality. Ninety-eight samples, collected simultaneously from the benthos and on macrophytes, were expressed as the logarithm of each species' relative abundance. WPGMA clustering, principal coordinates and discriminant analysis were used to describe and characterize differences between samples. Diversity was also computed to show the transformations of population structure due to differences in pollution levels. Prosobranch snails predominated in benthic populations while pulmonates characterized vegetation. A decrease in the number of species was the characteristic response to increasing pollution levels upon both types of substrates. High hydrocarbon levels were related to a decrease in the diversity of snail populations on the vegetation only. Predominance of prosobranchs in the benthos and pulmonates on the vegetation could be explained by a differential dependence of those two groups of snails on the aquatic medium, and by considering modes of nutrition. Sporadic oil spills affected the snail populations living on macrophytes .
A Comparison of Sampling Methods to Estimate Production Metrics of Littoral Zone Fish Based on Multi-Spatial Habitat Variables of a Manitoba Reservoir
ABSTRACT
Spatial modelling: a comprehensive framework for principal coordinate analysis of neighbour matrices (PCNM)
Ecological Modelling, Jul 1, 2006
... It can be constructed using distance criteria (select a distance threshold and connect all po... more ... It can be constructed using distance criteria (select a distance threshold and connect all points that are within that distance of each other), or more sophisticated procedures such as the Delaunay triangulation, Gabriel graph, relative neighbourhood graph, sphere of influence, or ...
Evolution and Determinants
Journal of Classification, Apr 1, 2009
We would like to thank the members of the LEMEE (Laboratoire d'Écologie Moléculaire et d'Évolutio... more We would like to thank the members of the LEMEE (Laboratoire d'Écologie Moléculaire et d'Évolution) of Université de Montréal for their constructive comments on a preliminary version of this manuscript as well as three anonymous reviewers. This study was supported by NSERC and FQRNT scholarships to VC and by NSERC grants OGP0007738 to PL and OGP0155251 to FJL.
Journal of Phycology, Sep 1, 1987
Thii paper ei'nluates ihe utilisation of space hy epihenthic diatom cells, as a responsf to emnro... more Thii paper ei'nluates ihe utilisation of space hy epihenthic diatom cells, as a responsf to emnronmeutal varia' tions. The aggregation pattern of fife species of epihenthic diatoms was quantified nnd compared to prm'ide evidenrf for thr significance of cell motility as an adaptive mechanismfor space occupation and monopoly. The epibenthic diatoms included (1) non-mobile colonial species forming either fan-shaped fSyncdra tabulata (Ag.) Kz.) or arborescent (Gomphonema kamtschaticum var. californicum Grun.) colonies: (2) stou-'mm-itig f'Cocconeis costata Greg, and Amphora pusioC/j, and (3)fast-moving fNaviculadirectaAV. Sm.)Ra.) non-colonialspeaes. The aggregation pattern of S. tabulata did not vary significantly among stx different light intensities manipulated in nature. The major patterns of aggregation were identified using analyiis of cmariance and dummy-variable regresiion. Highly mobile N. directa are significantly Ifsŝ gg^^g*tt^d fhan the four other diatom species. Son-mobile and s^lou'-moi'ing species show a similar, highly aggregated pattern. The occurrence of two patterns of spatial dispersion indicates that growth forms hear far-ranging ecological implications uith retpect to colonization .strategies, immigration, and possibly impact by grazers. An integrated model of grmith form characteristics, biological properties, and ecological implications is presented for epihenthic diatoms.
Environ Earth Sci, 2000
This paper describes a geostatistical technique based on conditional simulations to assess confid... more This paper describes a geostatistical technique based on conditional simulations to assess confidence intervals of local estimates of lake pH values on the Canadian Shield. This geostatistical approach has been developed to deal with the estimation of phenomena with a spatial autocorrelation structure among observations. It uses the autocorrelation structure to derive minimum-variance unbiased estimates for points that have not been measured, or to estimate average values for new surfaces. A survey for lake water chemistry has been conducted by the Ministère de l'Environnement du Québec between 1986 and 1990, to assess surface water quality and delineate the areas affected by acid precipitation on the southern Canadian Shield in Québec. The spatial structure of lake pH was modeled using two nested spherical variogram models, with ranges of 20 km and 250 km, accounting respectively for 20% and 55% of the spatial variation, plus a random component accounting for 25%. The pH data have been used to construct a number of geostatistical simulations that produce plausible realizations of a given random function model, while 'honoring' the experimental values (i.e., the real data points are among the simulated data), and that correspond to the same underlying variogram model. Post-processing of a large number of these simulations, that are equally likely to occur, enables the estimation of mean pH values, the proportion of affected lakes (lakes with pH^5.5), and the potential error of these parameters within small regions (100 km!100 km). The method provides a procedure to establish whether acid rain control programs will succeed in reducing acidity in surface waters, allowing one to consider small areas with particular physiographic features rather than large drainage basins with several sources of heterogeneity. This judgment on the reduction of surface water acidity will be possible only if the amount of uncertainty in the estimation of mean pH is properly quantified.