Should risk allocation strategies facilitate or hinder habituation to nonlethal disturbance in wildlife?

Flight initiation distance (FID), the distance at which an animal begins to flee from an approaching intruder, is commonly used to estimate the impact of human activities on wildlife. It reflects the level of risk tolerated by the animals. However, animals frequently approached by nonthreatening humans may progressively learn that there will be no adverse consequence for them, and thus perceive a reduced level of risk. I used an optimality model to study how this habituation process and risk allocation strategies could interact to determine FID. First, I computed the optimal FID for a foraging animal confronted with a single kind of threat. In this situation, the model predicts that FID should increase with the level of risk perceived during each encounter, and decrease when encounters become more frequent. Next, I used the model to explore what could happen after the arrival of nonthreatening humans in the environment, assuming that, initially, only predators were present. I studied how these environmental modifications could progressively affect the expectations of the forager, and its FIDs towards predators and humans. The model predicts that risk allocation strategies may either facilitate or impede habituation to nonlethal disturbance, with conflicting effects on the FIDs. Depending on the initial predation regime, the disturbance conditions created by humans and the number of predators that remain after human arrival, the animal may either progressively accept the presence of nonthreatening humans or retain a high level of sensitivity towards both predators and humans.