COS 141-2
A massive and a tiny keystone species interact to drive synergistic patterns of plant community structure and ecosystem heterogeneity in a Kenyan savanna
Understanding the causes and controls of community heterogeneity and structure has long been a goal of ecologists. In African savannas, both megaherbivores and termites are keystone taxa demonstrated to have profound impacts on plant communities and ecosystem function. Termites create mounds that create landscape heterogeneity by locally enriching soil, shifting plant palatability and community structure, and altering herbivory. Meanwhile, megaherbivore browsing can lead to reductions in tree and shrub density and diversity. Elephants in particular are known to radically affect landscape heterogeneity through changes in woody stands. While the effects of termites and megaherbivores have been studied separately, little work has been done to assess their potential interactions. Megaherbivores and termites may either compete for woody material or facilitate its availability, and may affect plant community structure either additively or synergistically.
I examined these interactions using the Kenya Long-term Exclosure Experiment (KLEE), which has excluded different combinations of large mammalian herbivores from replicated 4-ha plots for the past 19 years. I compared termite mound density, plant community composition, and plant community structure across large herbivore treatments. Using structural equation models and multivariate analysis, I analyzed how these keystone groups interact to influence plant community structure.
Results/Conclusions
Termites and megaherbivores interact in profound ways that strongly affect plant community structure and ecosystem heterogeneity. Megaherbivores (elephants, mostly) reduce tree density, and this leads to a reduction in termite mound density. Multivariate analysis shows plant communities on termite mounds are strikingly different from background plant communities, and that these differences are significantly increased by the presence of megaherbivores. Therefore, megaherbivores reduce the landscape heterogeneity produced by termites by reducing termite mound density, but may increase landscape heterogeneity by magnifying the ecological footprint of individual termite mounds. Overall, these results provide strong evidence for interactions between these two keystone taxa, which differ in body size by nearly ten orders of magnitude. This system is now being further studied to explore the factors influencing large-scale patterns in nutrient cycling, plant community composition, and community structure.