Factors that Determine Sleep Patterns
Some things that affect sleep are differences in body and brain size, prey-predator status, metabolic rate, and dwelling place. Small animals are at a higher risk for exposure to the cold than larger animals because the smaller the animal, the higher the ratio of body surface to body mass. This means that they lose heat more quickly than larger animals do. So, smaller animals should sleep longer to conserve energy. Unfortunately, because of their vulnerability, smaller animals actually have to adapt their sleep behavior and sleep less than their larger predators.
Another built-in difference that affects sleep is metabolic rate. Increased metabolic rate in small animals causes them to function more quickly in every way. This means that their sleep cycle finishes quickly. So, the length of NREM and REM cycles in animals is dependent upon body size, no matter how many hours an animal actually sleeps.
An ecological variable that affects sleep is predator-prey status. Unprotected animals cannot sleep for very long periods of time because they must always be alert. Therefore, having a REM brain activating system as part of their sleep is invaluable so that they can monitor the environment around them. This system guarantees that the animals of prey will be aware enough during sleep to prevent them from sleeping for too long a period of time and being captured by predators.
Another ecological variable that determines sleep patterns is dwelling place. Some animals of prey status are able to make their living places very high or very low and out of the way of predators. In this way, they can sleep efficiently and safely due to the location and characteristics of their dwelling place. An example of this is bats, which sleep safely by hanging from the ceiling of a cave (Hobson, 1995).