Every year, nearly two million wild herbivores cycle through the Serengeti-Mara ecosystem spanning Kenya and Tanzania in East Africa on the greatest terrestrial migration on earth. This isn’t one undifferentiated river of life. It’s a sequence – a modular procession of species, each occupying a distinct role. Zebra are the first to move, cropping the tall upper inflorescences of the grasses. Wildebeest follow days later, grazing the mid-level leaves exposed by the zebra’s work. Thomson’s gazelle trail behind, selecting the short, protein-rich regrowth and low-growing forbs revealed by both preceding waves. Each species processes the grassland differently, and the temporal separation between them creates boundaries – modules within the migration – that prevent direct competition from collapsing the system.