There are several theories about animal sleep:
lHibernation theory (Webb, 1974) lEvolutionary approach – sleep is assumed to confer a survival advantage lSleep helps conserve energy by: lReducing energy spent on behavioural activity lDrop in body temp & metabolic rate reduces energy lost as heat
Hibernation theory (Webb, 1974)
- Main prediction is that an animal’s sleep pattern will be determined by its energy intake & expenditure pattern
- Small animals will need more than large
- Diet (e.g. carnivore vs. herbivore) will affect sleep patterns
- Sleep will increase when energy loss goes up (cold) or energy intake goes down (food scarcity)
- Sleep is assumed to confer a survival advantage
- Sleep helps conserve energy by:
- Reducing energy spent on behavioural activity
- Drop in body temp & metabolic rate reduces energy lost as heat
Animal sleep patterns (vary by species)
3 hrs 4 hrs 8 hrs 12 hrs 16 hrs 20 hrs
- Comparative studies of different species generally support evolutionary view
- Smaller animals tend to sleep more than larger (e.g. giraffe 1hr vs. bat 20hrs)
- Carnivores sleep more than herbivores (e.g. lion 16hrs vs. buffalo 3hrs)
- lSome notable exceptions e.g. rabbit (small, herbivore) & human (much larger, omnivore) both sleep about 8hrs
- Sleep patterns are affected by energy expenditure & availability
- Animals generally sleep more when weather is cold and food is scarce
- However, no direct correlation between physical work done and sleep duration in humans
- Many evolutionary significant factors could affect sleep patterns; theory doesn’t tell us which are important
- Does a bat get so much sleep because it’s small or because it has few predators?
- Why do animals with very different lifestyles have similar sleep patterns?
- Some features of sleep cannot be explained easily by the hibernation theory:
- Why is sleep universal when in some species (e.g. dolphins) it would have been an advantage to get rid of it?
- Why is sleep deprivation apparently fatal?
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