Les présidents de l'alternance

Neuf pays africains se sont donnés, depuis 1990, des nouveaux présidents par la voie électorale. Les auteurs présentent les étapes de cette transition, les caractéristiques des élections, et le profil des présidents élus. L'impression qui domine est la diversité des situations et des hommes. (Résumé d'auteur

Different Approaches for Speaker Diarization

Audio diarization is the process of annotating an input audio channel with information that attributes (possibly overlapping) temporal regions of signal energy to their specific sources. These sources can include particular speakers, music, background noise sources and other signal source/channel characteristics. Speaker diarization is the task of determining “who spoke when?†in an audio or video recording that contains an unknown amount of speech and also an unknown number of speakers. Diarization can be used for helping speech recognition, facilitating the searching and indexing of audio archives and increasing the richness of automatic transcriptions, making them more readable. Over recent years, however, speaker diarization has become an important key technology for many tasks, such as navigation, retrieval or higher-level inference on audio data. Accordingly, many important improvements in accuracy and robustness have been reported in the area of conferences. The application domains, from broadcast news, to lectures and meetings, vary greatly and pose different problems, such as access to multiple microphones and multimodal information or overlapping speech

Uses of places and setting preferences in a French Antarctic station

The various uses of space as well as the environmental preferences of wintering people were investigated during 1 year in a French Antarctic station using daily participant observation (for uses of places) and a repeated measure of the perception and evaluation of the settings. The uses of places varied according to occupational and age subgroups: The young scientists expressed a higher need for privacy and a strong investment in their working areas, whereas the technicians preferred the social leisure area (main hall). These places were used as different behavior settings and thus corresponded to flexible environments. Flexibility was a characteristic of all the preferred places. A change in the preferences among the settings and the uses of places was also observed: After midwinter, the preferences evolved from private places to working areas. At the end of the mission, a behavioral change reflecting a stronger need for privacy was also observed

L'environnement en Afrique

Le débat sur l'environnement se prête à une série d'approximations. Ces dérives sont d'autant plus faciles lorsqu'il est question d'environnement en Afrique, que les informations sûres sont plus rares ou moins diffusées. Il est donc nécessaire de tenter d'approcher la réalité d'aussi prêt que possible. Dans cette perspective, les spécialistes de sciences de la nature et de sciences biologiques, notamment de l'ORSTOM, font le point des connaissances relatives à l'Afrique, acquises dans leur discipline respective. Chacun d'eux met l'accent sur des faits qui vont souvent à l'encontre des idées reçues, et sur la complexité étonnante des phénomènes analysés, qui s'oppose à une tendance naturelle à la simplification, voire à l'incantation, particulièrement forte sur ce thème. Les chercheurs en sciences sociales montrent que certaines corrélations simples ne résistent pas à la rude épreuve des faits ou à tout le moins, demandent à être nuancées. L'étude de l'environnement, c'est aussi d'autres acteurs, comme l'Etat, ou les bailleurs de fond, qui font désormais de l'environnement un axe important de leurs politiques de coopération Nord-Sud. Décrypter leurs actes et leurs discours, tenter d'entrevoir les enjeux politiques et économiques majeurs que représente l'environnement, ainsi que les risques de conflits dont il est porteur, s'imposai

NUEVO HOSPEDERO ALTERNO DEL PICUDO DEL PIMIENTO, ANTHONOMOUS EUGENII CANO EN PUERTO RICO

NUEVO HOSPEDERO ALTERNO DEL PICUDO DEL PIMIENTO, ANTHONOMOUS EUGENII CANO EN PUERTO RIC

Stream Invertebrate Responses to a Catastrophic Decline in Consumer Diversity

Tadpoles are often abundant and diverse consumers in headwater streams in the Neotropics. However, their populations are declining catastrophically in many regions, in part because of a chytrid fungal pathogen. These declines are occurring along a moving disease front in Central America and offer the rare opportunity to quantify the consequences of a sudden, dramatic decline in consumer diversity in a natural system. As part of the Tropical Amphibian Declines in Streams (TADS) project, we examined stream macroinvertebrate assemblage structure and production for 2 y in 4 stream reaches at 2 sites in Panama. One site initially had healthy amphibians but declined during our study (El Copé), and 1 site already had experienced a decline in 1996 (Fortuna). During the 1st y, total macroinvertebrate abundance, biomass, and production were generally similar among sites and showed no consistent patterns between pre- and post-decline streams. However, during the 2nd y, tadpole densities declined precipitously at El Copé, and total macroinvertebrate production was significantly lower in the El Copé streams than in Fortuna streams. Functional structure differed between sites. Abundance, biomass, and production of filterers generally were higher at Fortuna, and shredders generally were higher at El Copé. However, shredder production declined significantly in both El Copé reaches in the 2nd y as tadpoles declined. Nonmetric dimensional scaling (NMDS) based on abundance and production indicated that assemblages differed between sites, and patterns were linked to variations in relative availability of basal resources. Our results indicate that responses of remaining consumers to amphibian declines might not be evident in coarse metrics (e.g., total abundance and biomass), but functional and assemblage structure responses did occur. Ongoing, long-term studies at these sites might reveal further ecological consequences of the functional and taxonomic shifts we observed

Evidence for the Persistence of Food Web Structure After Amphibian Extirpation in a Neotropical Stream

Species losses are predicted to simplify food web structure, and disease‐driven amphibian declines in Central America offer an opportunity to test this prediction. Assessment of insect community composition, combined with gut content analyses, was used to generate periphyton–insect food webs for a Panamanian stream, both pre‐ and post‐amphibian decline. We then used network analysis to assess the effects of amphibian declines on food web structure. Although 48% of consumer taxa, including many insect taxa, were lost between pre‐ and post‐amphibian decline sampling dates, connectance declined by less than 3%. We then quantified the resilience of food web structure by calculating the number of expected cascading extirpations from the loss of tadpoles. This analysis showed the expected effects of species loss on connectance and linkage density to be more than 60% and 40%, respectively, than were actually observed. Instead, new trophic linkages in the post‐decline food web reorganized the food web topology, changing the identity of “hub” taxa, and consequently reducing the effects of amphibian declines on many food web attributes. Resilience of food web attributes was driven by a combination of changes in consumer diets, particularly those of insect predators, as well as the appearance of generalist insect consumers, suggesting that food web structure is maintained by factors independent of the original trophic linkages