Ecological theories propose that sleep is necessary to keep animals inactive when they do not need to engage in activities essential to their survival.
Meddis*- sleep is important as protection against predators, e.g, animals that rely on their sight to be immobile during darkness as they can't find food etc.
Those in danger of predators, sleep less than predators to remain alert
>> Pilleri's research supports this - dolphins in River Indus are in constant danger from floating Debris so only sleep for a few seconds at a time
>>Mukhametov 1984 - Bottlenose and porpoise dolphins are able to 'switch off' one of their cerebral hemispheres at a time enabling them to continously come up to the surface to breathe