The prey will be confused by the appearance of a new animal, and it will not be sure if it's a predator or harmless animal. This usually causes the prey animals big problems because that confusion usually leads to their death. Also the defensive system that the prey has developed is made for the predators it knows, but is usually ineffective with the newly introduced predators.
Since they are experiencing the arrival of a new specimen the animals that interact with the pnovel predator wont be aware that that animal is a new predator, so they will not run from him or hide form him, untill they learn from experience that the new novel predator is a predator and is hunting down the animals that are prey for him.
