Megaherbivory plant defense and trophic control in savanna ecosystems

Thu, Feb 8, 2018, 12:30 pm

Ecologists who work in savannas and grasslands often adhere to a non-equilibrial worldview, in which disturbances (fire, drought, catastrophic herbivory) prevent community and ecosystem properties from reaching equilibria. Conversely, many other ecologists view the world through a lens of trophic control, in which tightly coupled consumer-resource interactions stabilize the local abundance, distribution, and diversity of species. For fifteen years, my students and I have worked to understand if, how, and why trophic control operates in two African savannas. I will discuss three of my favorite findings from this body of work. First, I will demonstrate that fear of predation protects trees from a browsing ungulate, thus triggering a trophic cascade through which large carnivores make savanna tree communities less thorny. Next, I will show that a plant defense—ant mutualists—creates virtual monocultures of myrmecophytic trees, thereby preventing megaherbivores from transforming vast (hundreds of kilometers) swaths of savanna bushland to open grassland. Finally, I will discuss our use of classical consumer-resource theory to reduce apparent competition between co-occurring ungulates following large carnivore restoration. Although African savannas typically are envisioned as textbook examples of non-equilibrial ecosystems, trophic control can interact with non-equilibrial dynamics to shape the abundance, distribution, and diversity of species within this widespread biome.

Guyot 10
Open to the public

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