| Registro completo |
| Provedor de dados: |
ArchiMer
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| País: |
France
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| Título: |
Biodiversité et relations trophiques dans quelques milieux estuariens et lagunaires de l’Afrique de l’Ouest : Adaptations aux pressions environnementales
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| Autores: |
Villanueva, Ching-maria
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| Data: |
2004-10-20
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| Ano: |
2004
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| Palavras-chave: |
Milieux estuariennes et lagunaires
Relations trophiques
Adaptation
Ecopath
Reseaux neurones artificiels
Stress environnementaux
Maturité des écosystèmes
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| Resumo: |
This work is the result of a research on West African estuaries and lagoon ecosystems: estuaries of Sine-Saloum (Senegal) and the Gambia, (The Gambia), as well as the lagoons Ébrié (Ivory Coast) and Lake Nokoué (Benin). Estuaries and lagoons are highly productive and economically important ecosystems and are among those threatened as their biodiversity and productivity are constant exposed to various disturbances. These disturbances can weaken the stability and durability of these ecosystems. This led to the problematic raised in the thesis: To approach the African western ecosystems and the environmental pressures that they undergo that eventually affect the biodiversity and the trophic relations of their aquatic living resources. This work seeks to offer a precise analysis of the fish assemblages and to evaluate how the environmental changes affect the populations of brackish waters. It is necessary to integrate information on several water collections to arrive to a more complete comprehension of such ecosystems. The complex circumstances and strongly variables leading to situations of stress require a complete comprehension of the operation of these ecosystems. First, the concept of stress environmental, as well natural and/or human-related is presented. This demands the identification of the environmental factors which affect the dynamics and the interactions between the various biological compartments in order to explain the varying conditions of the ecosystems. After having presented each ecosystem and their respective aquatic resources, the author exposes the methodologies used for the analyses, as well employing ecological statistical analyses of populations based on experimental or collective fishing surveys to study the trophic relations existing within systems. The trophic interactions in these ecosystems were studied and compared in relation to various aspects of the environmental stress based on various ecological methods, supplemented by statistical analyses in particular the method of the comparison of abundance and the not supervised biomass (ABC) and neural networks (ANN), associated has a model trophodynamics, Ecopath. Complementary statistical ecological analyses such as not supervised analyses facilitated our analysis by defining the roles of the various groups and the intensity of the interactions between species which contribute to stabilize the ecosystems. The results obtained starting from the statistical studies highlight the differences in fish species assemblages according to in each ecosystem. The results starting from Ecopath indicate principal flows of energy among groups and raise interesting questions about the ecological concepts of stability and maturity of the ecosystems. The importance of detritus as support of the food chains is observed, especially in the event of limit of the primary production and even of the other sources of food. A reversed hypersalinity installed following Sahel drought in an estuary (Sine-Saloum), appears less harmful with the biodiversity than the effects of severe human activity diversified in a Beninese lagoon. The trophic relations appear based on the primary production in two ecosystems while detritus-based in the two others. The food sources of fish are not all fully utilized. The output of fishing activity and the biomass of the target groups are variable under the constrains of the ecosystem effect just like of the fishing effort itself. The convergence of the results concerning the biodiversity and the trophic relations in expressing terms of environmental stress is discussed in a final chapter. This is also a general conclusion and an outline of proposals for future research and management for a durable management of the resource. The significance of these ecosystems depends on the diversity of the habitats which play a part as refuge, feeding zone of food and access of migration that allows, in return, the survival of large populations. These habitats vary from the geographical point of view and by the environmental conditions which have effects over the aquatic communities and consequently on their contribution to the local economy. The comparison of geographically close ecosystems offers possibilities of generalization even if certain distinctive features especially make each ecosystem single as for its biological structure. This type of study is necessary for future management and conservations. Keywords : West Africa ; Biodiversity ; Trophic relations ; Adaptation ; Quantitative ecology ; System maturity
Le présent travail est le résultat de recherches sur des milieux estuariens et lagunaires de l'Ouest Africain. La notion de stress environnemental aussi bien naturel qu'anthropique est présentée; ce qui amène à formuler la problématique de la thèse: Aborder les écosystèmes ouest africains et les pressions environnementales qu'ils subissent et la façon dont celles-ci sont ressenties au niveau de la biodiversité et des relations trophiques. Les résultats obtenus mettent en évidence les différences dans les assemblages d'espèces dans le temps et l'espace selon des modalités variables dans chaque écosystème. Les conditions très variables et saisonnières du milieu et les habitats influencent la structure des écosystème et les relations existant entre ses ressources vivantes. Ceci résulte d’un processus d’élimination des espèces les moins rustiques dans un milieu et la propagation des organismes plus tolérants à ces différentes modifications. Les analyses comparatives montre que des circonstances inhabituelles comme une hyper-salinité inversée, installée à la faveur des sécheresses sahéliennes dans un estuaire, se révèlent moins nocives pour la biodiversité qu'une forte activité anthropique très diversifiée dans une lagune béninoise. Ceci provient des différences dans les mécanismes d’adaptation des organismes face à ces perturbations. Les relations trophiques se révèlent un indicateur utile de la stabilité et des possibilités de résistance (adaptation) aux stress. En effet, nous observons que la stabilité de ces écosystèmes repose plutôt sur la construction d’interactions complexes et diverses entre les espèces qui persistent que sur la complexité liée à la biodiversité. La résistance aux perturbations environnementales est susceptible d’être augmentée par l’efficacité des transferts d’énergie entre les différents niveaux trophiques. La convergence des résultats concernant la biodiversité et les relations trophiques en termes d'expression des stress environnementaux est discutée préalablement à une ébauche prudente de propositions de recherches futures et d'aménagement pour une gestion durable de la ressource.
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| Tipo: |
Text
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| Idioma: |
Francês
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| Identificador: |
http://archimer.ifremer.fr/doc/00180/29122/29305.pdf
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| Editor: |
Institut National Polytechnique de Toulouse
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| Relação: |
http://archimer.ifremer.fr/doc/00180/29122/
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| Formato: |
application/pdf
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| Direitos: |
2004 INP/ENSAT
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