Across the savannahs of Africa, millions of stomachs are busy converting plant tissue into animal flesh. The continent’s leaves and grasses are under constant assault from impala, wildebeest, buffalo, zebra, gazelles, and giraffes. Even acacia trees get bulldozed by elephants. There can be up to 25 species of these large plant-eaters in a given place, and many of them gather in gargantuan herds. How do they co-exist?

“It’s not obvious why competition for food doesn’t whittle the number of species down to just a few dominant competitors,” says Tyler Kartzinel from Princeton University. The prevailing idea says that different species have different food preferences. Grazers like zebra and wildebeest eat grass and little else. Browsers like dik-diks and giraffes nibble