Trophic resources and emergent food web attributes in rivers of the Lake Victoria Basin: a review with reference to anthropogenic influences

Abstract

The ecology of Lake Victoria and rivers draining its 180 000 km2 basin has changed over the past century in response to growing anthropogenic influences that have altered basal resources, trophic status and interactions and river flow regimes. Impacts on the ecology of the lake are well known, but little attention has focused on the ecological status of rivers supplying ecological services to the majority of the basin's over 30 million inhabitants. In this paper, we review existing research on the ecological status of streams and rivers in the Lake Victoria Basin (LVB) and evaluate how they fit into emerging models of riverine ecosystem function in the tropics. Studies to date indicate that allochthonous sources dominate inputs to food webs in forested headwaters and savanna mid‐reaches of rivers in the LVB, although transfer pathways vary with position in the river. Although riparian vegetation phenology and hydrologic run‐off pathways control the spatial and temporal fluxes of energy inputs in headwater streams; animals play increasingly important roles in savanna mid‐reaches. Over the last half century, food web studies have revealed widespread omnivory and a tendency toward increased omnivory among fishes whose diets were more specialized prior to the introduction of Lates niloticus and the ecological changes in the lake. Ecological patterns and processes in LVB rivers generally fit emerging models for the tropics, but studies completed to‐date do not find autotrophic energy sources to be important. The findings of this review highlight the importance of specific management actions and needs for future research. Copyright © 2012 John Wiley & Sons, Ltd.

Are Large Herbivores Vectors of Terrestrial Subsidies for Riverine Food Webs?

“…Most rivers draining into Lake Victoria have been cleared of hippo populations, which are currently confined to river mouths of major rivers and littoral areas around the lake and in many places they have been replaced by cattle (Masese and McClain 2012). The disparate conditioning of ingested organic matter by these two herbivores likely influences nutrient cycling and ecosystem dynamics, but comparative studies are limited.…”

Potential impacts of agricultural development on freshwater biodiversity in the Lake Victoria basin

“…Indeed, other studies have cited the limited environmental and ecological data on African streams as a key reason for using data from other temperate or tropical zones for developing management guidelines or interpreting human impacts on species (e.g. Kolding, van Zwieten, Mkumbo, Silsbe, & Hecky, 2008;Masese & McClain, 2012). The present database is taxonomically biased and does not specifically incorporate species endemic to the LVB.…”

“…The intensification of agriculture and the increased use of pesticides have also led to the contamination of water with pesticide residues (Getenga, Keng'ara, & Wandiga, 2004;Madadi, Wandiga, & Jumba, 2005;Wasswa, Kiremire, Nkedi-kizza, Mbabazi, & Ssebugere, 2011). Changes in the composition and level of material load in rivers and streams caused by land-use change has significant impacts on food webs throughout the LVB (Masese & Mcclain, 2012). The high human population density also contributes directly to nutrient pollution of the lake and rivers, as many small towns do not have sewerage systems (Nyenje, Foppen, Uhlenbrook, Kulabako, & Muwanga, 2010).…”

Balancing Water Resources Development and Environmental Sustainability in Africa: A Review of Recent Research Findings and Applications

“…During the past 70 years, the human population of the 180 000 km 2 lake catchment has grown from approximately 3.5 million to more than 30 million people, and pressures on land and water resources have grown proportionally (reviewed by Masese and McClain 2012). Water quality degradation in the lake and loss of biodiversity have received the most attention (Hecky et al 2010), but unmanaged expansion of croplands, cattle grazing, urbanization, and infrastructure have also severely degraded the basin’s natural landscapes and rivers (Odada et al 2009).…”

“…Large wildlife (e.g., wildebeest, giraffe, and elephants) have all but disappeared from inhabited areas, and even in and around protected areas like Masai-Mara National Reserve in Kenya, large wildlife abundances have decreased by 50 % over the past 30 years (Ogutu et al 2011). Increased erosion and nutrient runoff have contaminated rivers, and natural flow regimes and channel connectivity have been altered by dams, uncontrolled abstractions, and land use change (Masese and McClain 2012). Impacts on river and wetland ecosystems include biodiversity loss and alterations to fundamental ecosystem properties (Masese et al 2009; Raini 2009).…”