Species diversity and distribution-pattern determinants of African rivulines (Cyprinodontiformes: Nothobranchiidae) in rainforest streams of southern Cameroon

Understanding the community structure and ecology of fish populations in rainforest streams is a prerequisite for any actions towards their exploitation, management or conservation. We examined the community structure and species diversity of nothobranchiids (African rivulines) in rainforest streams of Cameroon's southern plateau and part of the coastal plain, using data on 19 environmental variables for ecological indices and multivariate analyses. In total, 1 019 individual cyprinodontiforms assigned to 14 species (largely species of Aphyosemion) were collected, for a global sampling effort of 78.6%. The presence of nothobranchiids in the study area was associated with several local environmental factors common to all sampling sites, mainly canopy cover above the watercourse and physicochemical characteristics of the stream habitat. Distribution of the species was strongly spatially structured, driven by the site's elevation and the water temperature, and influenced primarily by the riparian vegetation, substrate type, water conductivity and flow velocity. However, fish species richness did not differ significantly between the five sectors sampled and by elevation. The nothobranchiid communities were highly diverse (Shannon's H ' = 2.28 +/- 0.05; Pielou's J = 0.87) and the species evenly distributed. Seven species were exclusive to a single sector, others were prevalent in multiple sectors, and no species was common to all sectors. Affinities between species were relatively few, though there were exceptions, and most species tended to exclude each other. These findings highlight nothobranchiids as local fish assemblages having high biotic integrity and responsiveness to environmental degradation. In tropical Africa, these fishes often occupy fragile habitats influenced by anthropogenic activities. A better understanding of the unifying role of habitat in ecology will assist management efforts to promote biodiversity conservation.