Interaction Cascades in Anthropogenic Glades

Abstract

Pastoralism was traditionally, and is currently, one of the most pervasive and widespread livelihoods throughout East African savannas. After abandonment, livestock corrals in East African savannas develop into nutrient-rich, treeless “glades” that persist for decades. Other research has shown that glades have significantly higher concentrations of soil nutrients including nitrogen, potassium and carbon, which support several specialist grass species, and turning these patches long-term primary productivity hotspots. Using detailed observations, extensive sampling, and experimental methods, we demonstrate that these effects on primary productivity cascade up two trophic levels to increase abundance of insects and the gecko Lygodactylus keniensis. Extending previous research, we find that Acacia drepanolobium trees close to glade edges are larger and grow faster than those farther from the glade. Furthermore, we demonstrate experimentally that grasshoppers grow significantly faster inside glades than far away from glade edges and that arboreal insect abundance, biomass and diversity show the same significant trend. Finally, we find that geckos are significantly more abundant in trees close to the glade edge than far away. Our results show that traditional pastoral methods have significant impacts on multiple trophic levels at multiple scales and add important habitat heterogeneity to an otherwise homogenous landscape.