Global environmental change is putting increasing demands on freshwater resources. Three of the greatest threats to freshwater ecosystems are invasive species, over exploitation, and flow modification. These threats are manifestations of the human use of freshwater ecosystem services that illustrate the tradeoffs in services which will become more common. These drivers of environmental change all provide some set of ecosystem services while also reducing the provision of other services, making them excellent examples from which to draw guidance for future management.
The introduction of the freshwater fish Nile tilapia (Oreochromis niloticus) to the Kafue River, Zambia provides the motivation for the four studies presented here; each explores a particular tradeoff in ecosystem services that results from species invasions, overexploitation, and flow modification. A review of global tilapia introductions demonstrates that the ecological effects of tilapia invasion are ubiquitous, but perceptions of whether tilapia positively or negatively affect social well-being is dependent on socioeconomic background. I also show the introduction of Nile tilapia to the Kafue River has decreased genetic diversity and threatens the long-term production of both aquaculture and capture fisheries. I evaluate the value of the Kafue River fishery by modeling the tradeoff between fisheries production and hydropower generation, as imposed by dam-induced flow modification, and find that annual fishery production is $USD 7 million per year, but this production is not affected by flow modification. Finally, I consider how the harvest of invasive species may contribute to conservation goals, and demonstrate that market forces alone are unlikely to substantially reduced invasive populations because the value of harvest may supplant the value of other ecosystem services.
Overall, I break new ground on the extent and impacts of global tilapia introductions, the relationship between flow modification and fisheries production in a novel context, and the ongoing social and economic adaptation to species invasions. This research provides managers, policy makers and stakeholders new analyses and tools with which to better inform future decisions about tradeoffs in ecosystem services that accompany major global environmental changes.