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Papers by Pierre Legendre

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

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

Fundamental and Applied Limnology

Global Ecology and Biogeography

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

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 ...

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.

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 ...

Journal of Classification, Apr 1, 2009

Journal of Phycology, Sep 1, 1987