Mario Garrido, Valentín Pérez-Mellado and William E. Cooper Jr. Ethology Article first published online: 26 SEP 2014. DOI: 10.1111/eth.12322. Economic escape models predict escape decisions of prey which are approached by predators. Flight initiation distance (FID, predator–prey distance when prey begins to flee) and distance fled (DF) are major variables used to characterize escape responses. In optimal escape theory, FID increases as cost of not fleeing also increases. Leer más.