Some of the organisms have evolved in such a way that they remain inactive when the predator populations are active.
Adaptive theory of sleep suggests that the prey population prefer to sleep when (in this case, at night) the predators are most active. The prey population use this time in taking rest and restoring energy for other works. As the prey population is inactive and remained protected in safe places, they are less likely to be predated.
Hence, the correct answer is adaptive theory of sleeping.
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A hydrometer is an instrument that measures the specific gravity (relative density) of liquids. The ratio of the density of the liquid to the density of water. A hydrometer is usually made of glass, and consists of a cylindrical stem and a bulb weighted with mercury or lead shot to make it float
It is found in the understory or the lower canopy
