Food web dynamics

Abstract

Knowledge of the trophic structure and the major energy sources supporting metazoan production are important considerations for biodiversity conservation and ecosystem management. African streams and rivers face multiple stressors from agricultural intensification, deforestation, and municipal and industrial effluents coupled with uncontrolled water abstractions. Yet, the effects of these influences on ecosystem structure and functioning are poorly understood. In this chapter, we review the trophic dynamics of African riverine ecosystems with a focus on trophic structure, the major sources of energy supporting food webs, and the influence of human activities. While much of the data used for this review are from African studies, we also reference other studies in the tropics for comparison and to fill existing knowledge gaps. Based on available information, autochthony, short food chains, and an increased tendency toward omnivory characterize food webs in African streams and rivers. However, trophic interactions and dynamics in these systems are witnessing changes caused by human activities. Changes in trophic diversity and dynamics include shifts from allochthony to autochthony following the deforestation of forested headwater streams, top-down control of local fish and invertebrate populations caused by introduced predatory fish such as trout, and shrinkage of trophic niche sizes caused by land use change. Despite these developments, studies on food web structure and trophic dynamics are very limited in low-order streams, and we have identified future research needs that need to be addressed to fill knowledge gaps that would hinder biodiversity conservation and effective management of riverine ecosystems in African rivers, including their fisheries.