Walsh, Gina2024-01-242024-01-242024https://hdl.handle.net/10539/37402A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Science, School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, 2022Characterising functional freshwater biodiversity patterns and understanding community determinants can aid in predicting changes and prioritising specific conservation management actions. Afrotropical freshwater systems support diverse ecological communities, including many taxonomically undescribed species, yet few studies have been undertaken in this region and they remain poorly understood. Additionally, an overwhelming amount of research on north temperate streams has given rise to widely used lotic conceptual models which are superimposed over freshwaters globally, though the theory governing the structure of Afrotropical lotic communities remains largely unexplored. In this thesis I explored different aspects of the biodiversity, trophic ecology and functional diversity of an Afrotropical system in the Republic of Congo (west Central Africa) through a series of field studies. I formally describe two new to science fish species collected in the region, and use fish functional traitbased approaches to explore the functional diversity of fish assemblages and test selected expectations of riverine conceptual models in this regional setting. Following, I used carbon and nitrogen stable isotopes (δ13C, δ15N) from samples collected along a continuum of a coastal river in the Republic of the Congo to show temporal and spatial patterns of trophic diversity and basal carbon resource use. In addition to uncovering new fish diversity, I established that whilst tenets of certain conceptual models such as the River Continuum Concept and the River Habitat Template were supported by fish trait-environment relationships, unique patterns of functional diversity also exist which are scale dependent and result in different functional strategies driving communities between upper and lower positions in the basin. At sub-basin scale, headwater zones harbour substantial functional diversity in relation to upstream catchment size, and results suggest that historical forest refugia may play a role in the high functional richness at high elevations of the region. Isotopic analysis revealed that river order and season are important drivers in consumer trophic strategies along a river continuum in the wet Afrotropics, and that riparian forest sources are key basal carbon resources supporting consumers. Isotopic work reiterated that headwaters are distinctive in terms of trophic and functional diversity. I discovered potential evidence for methanogenic pathways in lateral swamp forests that may subsidize instream food webs. The outcomes of this work demonstrate that existing river conceptual models only partially explain patterns of richness and functional diversity of river systems in this region, and highlights the importance of understanding mechanisms structuring regional functional diversity (e.g. nestedness and turnover) in efforts to conserve freshwater systems. It also emphasizes the need for swamp forest- and riparian specific policies in central Africa to be incorporated into freshwater conservation plans and strategies for forested regions of the Afrotropics.enFreshwaterBiodiversityAfrotropical freshwaterThesis