Community stability and turnover in changing environments

Les communautés d'êtres vivants peuvent elles êtres considérées comme des organismes complexes, ou au contraire comme de simples groupes d'espèces, individuelles ? Cette question est à l'origine de nombreux débats en écologie, ces deux visions impliquant notamment des prédictions très différentes dans les patrons spatiaux et temporels de communautés. Lorsque l'environnement change graduellement dans l'espace ou dans le temps, la vision individualiste implique des changements graduels dans la composition des communautés, tandis que la vision du "super-organisme" prédit des changements davantage abrupts. L'objectif principal de cette thèse est de comprendre et déterminer sous quelles conditions ces différents types de réponse des communautés aux changements de l'environnement peuvent advenir. Dans une première partie, nous étudions le rôle que la compétition inter-spécifique peut jouer dans l'émergence de différents patrons spatiaux de communautés. Nous étudions notamment les conditions théoriques sous lesquelles la compétition peut faire apparaître des patrons graduels ou discontinus dans la composition des espèces. Dans une deuxième partie, nous étudions l'influence des interactions entre les espèces et leur environnement sur les patrons spatiaux de communautés. Nous montrons notamment comment des phénomènes de construction de niche peuvent mener à l'émergence de changements brutaux dans la composition des communautés, mais également dans les conditions de l'environnement. Enfin, dans une dernière partie, nous illustrons le rôle que peut jouer la biodiversité dans la protection des écosystèmes face à des effondrements écologique, et notamment le rôle que peut jouer la biomasse dans cette protection.The question whether communities should be viewed as superorganisms or loose collections of individual species has been the subject of a long-standing debate in ecology. Each view implies different spatial and temporal community patterns. When environment gradually changes in space or in time, the organismic view predicts that species turnover is discontinuous, while the individualistic view predicts gradual changes in species composition. The main objective of this thesis is to understand the theoretical conditions under which these various types of community response can occur. First, I study the role of interspecific competition can play in the emergence of various spatial community patterns. I investigate the theoretical conditions in competition under which smooth or discrete spatial patterns can emerge. Then, I study how interactions between species and their environment can lead to various community patterns in space. I notably show how ecological niche construction can lead to the emergence of abrupt changes in species composition and in the environment, and the role biodiversity plays therein. Finally, I focus on the role biodiversity can play against ecosystem collapse. In this section, I illustrate how diversity loss, through its effects on total biomass, can lead to ecosystem collapse

Cadre conceptuel pour l'étude de la mise en oeuvre des politiques en éducation

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal

Detection of significant climatic precession variability in early Pleistocene glacial cycles

Despite having a large influence on summer insolation, climatic precession is thought to account for little variance in early Pleistocene proxies of ice volume and deep-water temperature. Various mechanisms have been suggested to account for the dearth of precession variability, including meridional insolation gradients, interhemispheric cancellation of ice-volume changes, and antiphasing between the duration and intensity of summer insolation. We employ a method termed Empirical Nonlinear Orbital Fitting (ENOF) to estimate the amplitudes of obliquity and precession forcing in early Pleistocene proxies and their respective leads or lags relative to the timing of orbital variations. Analysis of a high-resolution North Atlantic benthic δ18O record, comprising data from IODP sites U1308 and U1313, indicates a significantly larger precession contribution than previously recognized, with an average precession-to-obliquity amplitude ratio of 0.51 (0.30-0.76 95% confidence interval) in the rate-of-change of δ18O between 3 and 1 Ma. Averaged when eccentricity exceeds 0.05, this ratio rises to an average of 1.18 (0.84-1.53). Additional support for precession’s importance in the early Pleistocene comes from its estimated amplitude covarying with eccentricity, analyses of other benthic δ18O records yielding similar orbital amplitude ratios, and use of an orbitally-independent timescale also showing significant precession. Precession in phase with Northern Hemisphere summer intensity steadily intensifies throughout the Pleistocene, in agreement with its more common identification during the late Pleistocene. A Northern Hemisphere ice sheet and energy balance model run over the early Pleistocene predicts orbital amplitudes consistent with observations when a cooling commensurate with North Atlantic sea surface temperatures is imposed. These results provide strong evidence that glaciation is influenced by climatic precession during the late Pliocene and early Pleistocene, and are consistent with hypotheses that glaciation is controlled by Northern Hemisphere summer insolation.NERC NE/R000204/1 EPSRC EP/S030417/

Growth and adaptation of microorganisms on the cheese surface

Cet article a été publié une nouvelle fois dans le numéro 362 http://femsle.oxfordjournals.org/content/362/1/1.20#sec-1Microbial communities living on cheese surfaces are composed of various bacteria, yeasts and molds that interact together, thus generating the typical sensory properties of a cheese. Physiological and genomic investigations have revealed important functions involved in the ability of microorganisms to establish themselves at the cheese surface. These functions include the ability to use the cheese's main energy sources, to acquire iron, to tolerate low pH at the beginning of ripening and to adapt to high salt concentrations and moisture levels. Horizontal gene transfer events involved in the adaptation to the cheese habitat have been described, both for bacteria and fungi. In the future, in situ microbial gene expression profiling and identification of genes that contribute to strain fitness by massive sequencing of transposon libraries will help us to better understand how cheese surface communities function

Accountability in the French nonprofit sector: From the inside out.

The thesis aims to explain increasing accountability in the French nonprofit sector. The qualitative research investigates the hypothesis that engendering trust is the key rationale for increasing accountability. The research also explores inductively other potential rationales for increasing accountability (e.g. corporatisation, integration of international standards of accountability, donor pressure, and the media). US regulatory, self-regulatory, and voluntary models of accountability provide reference standards. The study targets 45 renowned French NPOs. 33 are members of a national independent accountability accreditation organisation (Comite de la Charte de Deontologie), and 12 comprise a control group. The driving voice is the perspective of the most senior leaders of respondent organisations, almost all executive directors, board Presidents, or board members. The theoretical framework centres on Henry Hansmann's theory of trust (derived from legal restrictions on profit distribution or the "nondistribution constraint') as an explanation for the origin and on-going efficacy of the nonprofit form. First establishing the relevance of Hansmann's demand side theory in France, the analysis then bridges Hansmann's rationale for the nonprofit organisational structure to analysis of how and why French NPOs supplement the intrinsic characteristics of that structure with accountability. Hansmann might call this organisational effort the "supply side." Finally, the emerging spectrum from Hansmann's trust to Lester Salamon's suggestion that accountability is the modern foundation for trust because the nondistribution constraint no longer suffices also frames the analysis. The proposed definition of accountability combines a general definition and an operationalised definition (derived from scholarly literature and best practice, respectively). The analysis highlights organisations' strategic assessment of quantitative/non-quantitative considerations in accountability-related decisions, including the impact of specified internal organisational variables and external contextual variables. The most oft-cited rationale for increasing accountability is ethical, effective management, followed by donor trust. Donor trust proves essential and fragile - irrespective of cited rationale for increasing accountability

Factors Influencing the Transferability of Maintenance Standards for Low-Volume Roads

Among the many parameters that influence the selection of maintenance strategies for unpaved roads, two factors have been selected in this paper to illustrate that caution needs to be exercised when attempting to transfer policies or standards from one set of conditions to another. These two factors are factor costs (not budgets) and material resources. Broadly speaking, the definition of a maintenance policy for an unpaved network implies that besides routine activities such as vegetation control and ditch and culvert cleaning, consideration should be given to the frequency of grading and also to the timing of graveling operations. Drawing from the experience collected in two widely different environments, one in the equatorial forest region of central Africa-where maintenance costs are high and gravel resources scarce-and the other in northeast Brazil, it is shown that maintenance standards are highly dependent not only on traffic volume but also on the properties of surfacing materials and the unit cost of grading. As shown and explained in this paper, the optimum grading frequency derived from economic analyses for a given volume of traffic may vary by a factor of 5, ranging between 2 and 10 times per year. Similarly, the threshold value of traffic volume at which surfacing an earth road with gravel becomes economically justified can range from below 20 to more than 100 vehicles per day, depending on cost of graveling and physical properties of the subgrade to be graveled. Such wide variations suggest the need for a careful definition of local conditions before an attempt is made to transfer maintenance standards across countries or even across regions within a country. Even under the best maintenance policy, vehicle operating costs on unpaved roads are usually 10 to 30 percent higher than those on well-maintained paved roads, mostly because of differences in average surface roughness conditions. Furthermore, the neglect of maintenance on an unpaved network may cause vehicle operating costs to increase by a factor of 2 to 3, because roughness can rise quickly from 5 m/km international roughness index (IRI) (on a newly graded road) to upward of 20 m/km within a few weeks if traffic volume is high. On paved roads, the situation is different: not only is the rate of progression of roughness slower, but also a smalle~. range of values is observed between a pavement in good condition (IRI = 3) and the same pavement at the end of its useful life, that is, in poor condition (IRI = 6 to 8), with the difference in vehicle operating costs generally not more than 30 percent. Therefore, maintaining a network of unpaved roads requires relentless attention as well as a well-defined program of recurrent activities in order to keep the level of service of the roads within acceptable limits. Among the recurrent activities to be carried out, grading and graveling operations are the primary maintenancerelated determinants of road conditions, and in tum of the cost of operating vehicles. The World Bank, 1818 H St. N.W., Washington, D.C. 20433. The frequency at which bladings are to be performed and the timing at which an unpaved road is to be surfaced or resurfaced with gravel constitute the basic requirements of any rationally designed maintenance program, and methods are now available that enable the definition of optimum standards both for grading frequencies and for appropriate timing of gravel surfacing (1-3). However, these standards are strongly dependent upon local conditions and a number of parameters such as traffic, level of service required, the importance of the road, climate (in particular, rainfall), budget constraints, material resources, and unit costs of grading and graveling. In this paper, the effect of the last two parameters is evaluated. EFFECT OF MATERIAL RESOURCES ON MAINTENANCE STANDARDS Grading Frequency Depending on the availability of materials, the wearing course of unpaved roads may consist of a wide variety of soils, ranging from fine-grained silts or clays to fairly coarse gravel. Although the rate of surface deterioration is mostly influenced by traffic volumes, roughness progression is also governed by the physical and geotechnical properties of the surfacing material, that is, its particle size distribution and plasticity

Diabetes, Periodontitis and The Oral Microbiome

The association between diabetes mellitus and periodontitis has been studied thoroughly. However, the role of the oral microbiome in linking these two diseases still is not clear. The objective of this literature review is to search the current studies on oral dysbiosis in the two diseases and find out whether the oral microbiome could be a possible biomarker indicating diabetes in periodontal patients

Reemergence of Syphilis in Martinique, 2001–2008

Syphilis reemerged in Martinique in 2004 and initially affected 3 HIV-infected patients. By March 2008, syphilis was diagnosed for 37 men and 18 women. As of October 31, 2009, this outbreak had not yet been brought under control. It initially affected mainly men who had sex with men before it spread to heterosexual persons, minority group members, and crack cocaine users

Detection of significant climatic precession variability in early Pleistocene glacial cycles

Despite having a large influence on summer insolation, climatic precession is thought to account for little variance in early Pleistocene proxies of ice volume and deep-water temperature. Various mechanisms have been suggested to account for the dearth of precession variability, including meridional insolation gradients, interhemispheric cancellation of ice-volume changes, and antiphasing between the duration and intensity of summer insolation. We employ a method termed Empirical Nonlinear Orbital Fitting (ENOF) to estimate the amplitudes of obliquity and precession forcing in early Pleistocene proxies and their respective leads or lags relative to the timing of orbital variations. Analysis of a high-resolution North Atlantic benthic record, comprising data from IODP sites U1308 and U1313, indicates a larger precession contribution than previously recognized, with an average precession-to-obliquity amplitude ratio of 0.51 (0.30-0.76 95% confidence interval) in the rate-of-change of between 3 and 1 Ma. Averaged when eccentricity exceeds 0.05, this ratio rises to 1.18 (0.84-1.53). Additional support for precession's importance in the early Pleistocene comes from its estimated amplitude covarying with eccentricity, analyses of other benthic records yielding similar orbital amplitude ratios, and use of an orbitally-independent timescale also showing significant precession. Precession in phase with Northern Hemisphere summer intensity steadily intensifies throughout the Pleistocene, in agreement with its more common identification during the late Pleistocene. A Northern Hemisphere ice sheet and energy balance model run over the early Pleistocene predicts orbital amplitudes consistent with observations when a cooling commensurate with North Atlantic sea surface temperatures is imposed. These results provide strong evidence that glaciation is influenced by climatic precession during the late Pliocene and early Pleistocene, and are consistent with hypotheses that glaciation is controlled by Northern Hemisphere summer insolation