A recent study examined the daytime and nighttime activity patterns of two populations of tree-dwelling lemurs -- the first living in a rain forest, where tree canopy cover is consistent year-round, and the second living in a deciduous forest, where many trees lose their leaves during the winter months. Both groups of lemurs were found to be more nocturnal during winter months than they were the rest of the year. However, the winter increase in nocturnal activity was significantly more pronounced for the population living in the deciduous forest than it was for the population living in the rain forest. Which one of the following, if true, most helps to explain the difference between the two lemur populations with respect to winter activity patterns? ['The primary predators for both lemur populations are high-flying birds that rely on their eyesight to hunt prey during daylight.', 'In both habitats, species of predatory snakes active during daylight are most active during winter months.', 'For both lemur populations, the primary competitors for food resources are species active during daylight.', 'The lemur population in the rain forest eats both plants and insects whereas the population in the deciduous forest eats only plants.']