35 research outputs found
Variabilité à long terme des peuplements de poissons : résultats provenant de rivières françaises et ouest africaines
La variabilité à long terme de 18 peuplements de poissons a été étudiée dans des rivières françaises et ouest africaines. Les principaux résultats sont les suivants : 1) le coefficient de variation (CV) de la richesse spécifique, le CV de l'abondance totale et le CV moyen des espèces constitutives du peuplement augmentent avec la durée de l'étude; 2) selon la classification proposée par GROSSMAN et al. (1990) basée sur le CV moyen de l'abondance des espèces, tous les peuplements étudiés rentrent dans la catégorie des peuplements à fortes fluctuations interannuelles. Cependant certaines populations (les salmonidés en Bretagne par exemple) présentent une faible variabilité de leur densité; 3) dans le Rhône, les peuplements dont les populations manifestent une grande variabilité interannuelle sont ceux présentant le plus grand taux de renouvellement en espèces. Ce résultat est en accord avec l'hypothèse de HORWITZ (1978, "extermination hypothesis"). (Résumé d'auteur
Cryptic Diversity of African Tigerfish (Genus Hydrocynus) Reveals Palaeogeographic Signatures of Linked Neogene Geotectonic Events
The geobiotic history of landscapes can exhibit controls by tectonics over biotic evolution. This causal relationship positions ecologically specialized species as biotic indicators to decipher details of landscape evolution. Phylogeographic statistics that reconstruct spatio-temporal details of evolutionary histories of aquatic species, including fishes, can reveal key events of drainage evolution, notably where geochronological resolution is insufficient. Where geochronological resolution is insufficient, phylogeographic statistics that reconstruct spatio-temporal details of evolutionary histories of aquatic species, notably fishes, can reveal key events of drainage evolution. This study evaluates paleo-environmental causes of mitochondrial DNA (mtDNA) based phylogeographic records of tigerfishes, genus Hydrocynus, in order to reconstruct their evolutionary history in relation to landscape evolution across Africa. Strong geographical structuring in a cytochrome b (cyt-b) gene phylogeny confirms the established morphological diversity of Hydrocynus and reveals the existence of five previously unknown lineages, with Hydrocynus tanzaniae sister to a clade comprising three previously unknown lineages (Groups B, C and D) and H. vittatus. The dated phylogeny constrains the principal cladogenic events that have structured Hydrocynus diversity from the late Miocene to the Plio-Pleistocene (ca. 0–16 Ma). Phylogeographic tests reveal that the diversity and distribution of Hydrocynus reflects a complex history of vicariance and dispersals, whereby range expansions in particular species testify to changes to drainage basins. Principal divergence events in Hydrocynus have interfaced closely with evolving drainage systems across tropical Africa. Tigerfish evolution is attributed to dominant control by pulses of geotectonism across the African plate. Phylogenetic relationships and divergence estimates among the ten mtDNA lineages illustrates where and when local tectonic events modified Africa's Neogene drainage. Haplotypes shared amongst extant Hydrocynus populations across northern Africa testify to recent dispersals that were facilitated by late Neogene connections across the Nilo-Sahelian drainage. These events in tigerfish evolution concur broadly with available geological evidence and reveal prominent control by the African Rift System, evident in the formative events archived in phylogeographic records of tigerfish
Longitudinal river zonation in the tropics: examples of fish and caddisflies from endorheic Awash river, Ethiopia
Primary Research PaperSpecific concepts of fluvial ecology are
well studied in riverine ecosystems of the temperate
zone but poorly investigated in the Afrotropical
region. Hence, we examined the longitudinal zonation
of fish and adult caddisfly (Trichoptera) assemblages
in the endorheic Awash River (1,250 km in length),
Ethiopia. We expected that species assemblages are
structured along environmental gradients, reflecting
the pattern of large-scale freshwater ecoregions. We
applied multivariate statistical methods to test for differences in spatial species assemblage structure and
identified characteristic taxa of the observed biocoenoses
by indicator species analyses. Fish and
caddisfly assemblages were clustered into highland
and lowland communities, following the freshwater
ecoregions, but separated by an ecotone with highest
biodiversity. Moreover, the caddisfly results suggest
separating the heterogeneous highlands into a forested
and a deforested zone. Surprisingly, the Awash
drainage is rather species-poor: only 11 fish (1
endemic, 2 introduced) and 28 caddisfly species (8
new records for Ethiopia) were recorded from the
mainstem and its major tributaries. Nevertheless,
specialized species characterize the highland forests, whereas the lowlands primarily host geographically
widely distributed species. This study showed that a
combined approach of fish and caddisflies is a
suitable method for assessing regional characteristics
of fluvial ecosystems in the tropicsinfo:eu-repo/semantics/publishedVersio
Effects of natural and anthropogenic environmental changes on riverine fish assemblages: a framework for ecological assessment of rivers
Onchocerciasis Control Programme in West Africa: a 20-year monitoring of fish assemblages
Functional diversity of soil microbial community, rock phosphate dissolution and growth of Acacia seyal as influenced by grass-litter and soil-feeding termite nest structure amendments
International audienc
Onchocerciasis control programme in West Africa: ten years monitoring of fish populations
Commencing in 1975, under the auspices of W.H.O., weekly applications of insecticides have been employed to control the blackfly which transmits human river blindness in West Africa. The results provided in this paper do not show, as a whole, any clear impact of OCP-applied pesticides on fish populations. The total catch, the number of species caught in each sample and coefficient of condition, appeared to fluctuate around a mean value, and no long-term drop was observed over the period investigated. The seasonal pattern is generally clear. In some cases longer term declines occur, generally being followed by a rise correlating with changing hydrological conditions