284 research outputs found

    Le Comité Paul Rose

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    Habitat Use by Brood-Rearing Waterfowl in Subarctic Québec

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    Aerial surveys of waterfowl were conducted in subarctic Quebec in 1989 and 1990 on randomly selected 100 sq km plots. We used logistic regression for modelling relationships betweren the presence of waterfowl broods and habitat characteristics. For each species, models of habitat use were generated with one data set and tested with two others. We also compared the frequency distributions of broods of each species in different habitat types. Correct-classification rates of models varied betweren 0.53 and 0.77. Sensitivity of models generally increased when applied to validation data sets. Models showed that green-winged teals (Anas crecca) avoided lakes >501 ha and used vegetated lakes, ponds and fens or bogs more than predicted by their availability. Black scoters (Melanitta nigra) and surf scoters (M. perspicillata) were found mostly on small lakes (<10 ha) and medium lakes (10-100 ha). Black scoters were associated with the presence of ponds and lakes with sedge and grass, whereas surf scoters were not. The presence of scaup (Aythia spp.) broods was associated with the presence of vegetation. Green-winged teals were observed more often on bogs than were either scoters or scaups. Black scoters were observed more often on ponds and less often on medium-sized lakes than surf scoters and scaups. The latter differed in their use of lakes <10 ha: surf scoters, like black scoters, mostly used unvegetated lakes, while scaups and green-winged teals mostly used vegetated lakes. The accuracy and precision of logistic models may be enhanced by additional habitat variables, careful selection of sample-cell size and further investigation of the breeding biology of the surveyed species.Key words: habitat, model, logistic regression, northern Québec, black scoter, surf scoter, green-winged teal, scaup, broodDes inventaires aériens de sauvagine dans des parcelles de 100 km² sélectionnées aléatoirement ont été réalisés dans le Québec subarctique en 1989 et en 1990. La régression logistique fut utilisée pour modéliser les relations entre la présence de couvées et des paramètres d'habitat. Des modèles d'utilisation d'habitat ont été générés à l'aide d'une série de données et validés à l'aide de deux autres. Nous avons aussi comparé les distributions de fréquences des couvées des espèces étudiées dans divers types de biotopes. Les taux de classification correcte des modèles ont varié entre 0.53 et 0.77. De façon générale, la sensibilité des modèles augmentait lorsque ces derniers étaient appliqués aux données de validation. Les modèles montrent que la Sarcelle à ailes vertes (Anas crecca) a utilisé les plans d'eau avec de la végétation, les étangs et les tourbières et a évité les lacs > 501 ha. Les macreuses (Melanitta nigra, M. perspicillata) ont surtout été vues sur des lacs de petite (< 10 ha) et moyenne (10-100 ha) superficies. Les Macreuses à bec jaune se démarquaient des Macreuses à front blanc en étant associées à la présence d'étangs et de lacs avec des herbaçaies. La présence de couvées de morillons (Aythia spp.) dans les cellules était associée à celle de végétation. La Sarcelle à ailes vertes fut observée plus souvent dans les tourbières que les autres espèces. La Macreuse à bec jaune fut observée plus souvent sur des étangs et moins souvent sur des lacs de superficie moyenne que la Macreuse à front blanc et les morillons. Ces dernières espèces différaient dans leur utilisation de lacs <10 ha: les Macreuses à front blanc, comme les Macreuses à bec jaune, utilisaient surtout les lacs aux rives sans végétation alors que les morillons et les sarcelles utilisaient surtout des lacs avec végétation. La précision des modèles de régression logistique pourrait être augmentée par l'utilisation de paramètres d'habitat supplémentaires, un choix différent de la taille de l'unité de mesure et une meilleure connaissance de l'écologie des espèces cibles.Mots clés: habitat, modèle, régression logistique, Québec, Macreuse à bec jaune, Macreuse à front blanc, Sarcelle à ailes vertes, Morillons, couvé

    Gallot-Tanno Theorem for closed incomplete pseudo-Riemannian manifolds and applications

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    We extend the Gallot-Tanno Theorem to closed pseudo-Riemannian manifolds. It is done by showing that if the cone over a manifold admits a parallel symmetric (0,2)(0,2)-tensor then it is Riemannian. Applications of this result to the existence of metrics with distinct Levi-Civita connections but having the same unparametrized geodesics and to the projective Obata conjecture are given. We also apply our result to show that the holonomy group of a closed (O(p+1,q),Sp,q)(O(p+1,q),S^{p,q})-manifold does not preserve any nondegenerate splitting of Rp+1,q\R^{p+1,q}.Comment: minor correction

    Effects of Local and Landscape Factors on Population Dynamics of a Cotton Pest

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    BACKGROUND: Many polyphagous pests sequentially use crops and uncultivated habitats in landscapes dominated by annual crops. As these habitats may contribute in increasing or decreasing pest density in fields of a specific crop, understanding the scale and temporal variability of source and sink effects is critical for managing landscapes to enhance pest control. METHODOLOGY/PRINCIPAL FINDINGS: We evaluated how local and landscape characteristics affect population density of the western tarnished plant bug, Lygus hesperus (Knight), in cotton fields of the San Joaquin Valley in California. During two periods covering the main window of cotton vulnerability to Lygus attack over three years, we examined the associations between abundance of six common Lygus crops, uncultivated habitats and Lygus population density in these cotton fields. We also investigated impacts of insecticide applications in cotton fields and cotton flowering date. Consistent associations observed across periods and years involved abundances of cotton and uncultivated habitats that were negatively associated with Lygus density, and abundance of seed alfalfa and cotton flowering date that were positively associated with Lygus density. Safflower and forage alfalfa had variable effects, possibly reflecting among-year variation in crop management practices, and tomato, sugar beet and insecticide applications were rarely associated with Lygus density. Using data from the first two years, a multiple regression model including the four consistent factors successfully predicted Lygus density across cotton fields in the last year of the study. CONCLUSIONS/SIGNIFICANCE: Our results show that the approach developed here is appropriate to characterize and test the source and sink effects of various habitats on pest dynamics and improve the design of landscape-level pest management strategies

    Money for writing: Screenplay development and screenwriters earnings in French cinema

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    The funds allocated to developing screenplays currently constitute on average 2 to 3% of the overall budget of a film in France. Producers are more than ever dependent on presenting attractive draft screenplays to find their financial partners. As a result, screenwriters undoubtedly are active economic partners of production planning, but they do not seem to receive much professional recognition for this vital role. Moreover, their earnings often fail to reflect the amount of work produced and do not reward adequately the risks taken, including the possibility that production could stop after the screenplay is written. This article investigates the place of screenplay development within the economics of French cinema. Using recently published official reports and interviews, the author identifies different types of screenwriters – freestanding screenwriters, writing teams and screenwriters co-writing with the director – and addresses their working conditions. She surveys some of the contract modalities for the remuneration of professional screenwriters. Finally, she reviews the proposals made by different professional bodies to improve the remuneration of screenwriters and reform the financing of screenwriting
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