Ecosystem Engineers on Kenya’s Laikipia Plateau: Analyzing the Effects of Large Megafauna on the Ecohydrology of a Semi-arid Kenyan Savanna Landscape

Abstract

Large megafauna are ecosystem engineers and have great influence upon their landscapes. However, they are disappearing from the world at unprecedented rates. Now more than ever, it is critical to understand how the extirpation of these animals is affecting their respective ecosystems, specifically on the the ecohydrology of the landscape, which has not been thoroughly studied. The objective of this work was to develop a model that can determine how the level of rainwater runoff in the landscape changes with based off of the presence, or lack thereof, of megafauna in the ecosystem. This study was carried out at the Mpala Research Center in the center of the Laikipia Plateau in Kenya, one of the last places in East Africa where large megafaunal populations are relatively stable even in the presence of humans, and focused on ‘game trails,’ small pathways created by the constant movement of animals. Utilizing an in-depth study of a few of these trails, we characterized the nature of the soil and vegetation both on and away from each trail as well as the usage by different megafauna. We found that during smaller rainfall events, the trails actually produced less runoff, with the opposite occurred during large rainfall events. Using advanced drone imagery of that same landscape, we mapped the overall network of the game trails. These results were then synthesized within a MatLab model of soil moisture over a 2000 day period to calculate exactly what effect these megafauna were having upon the landscape. We found that the game trail network was quite large, having 29.44km of trails, and had a significant effect upon the runoff properties of the landscape. Over time, the trails themselves contributed more to runoff than regular patches of vegetation. When ~90% megafauna are removed from the landscape, there is up to a 20.94% decrease in the level of runoff that occurs on the landscape.