Theory 30/Grassland & Savanna/Migration
Migration Follows Quality Against Risk
The claim
Migratory herds move when the ratio of grass quality to predation risk falls below a threshold, not when grass is exhausted.
01Mechanism
Animals trade nutrition against danger; they leave before the resource is gone because the risk rises faster than the benefit falls.
02Prediction
Departure should track the ratio.
03Refutation
Departure tracking grass biomass would remove predation.