The fact that both lemur populations’ competitors are active during daylight has nothing to do with tree canopy cover and does not explain why lemurs in the deciduous forest had much more nocturnal activity than those in the rainforest.

Lemurs in deciduous forests face greater predation risk in winter because the birds can see clearly without leaves. In rainforests, year-round leaves block these predators' view. Thus, to avoid predators, lemurs in deciduous forests are more active at night during the winter.

This might explain why both populations are more nocturnal during the winter. However, because the snakes’ hunting isn’t affected by tree canopy cover, it doesn’t explain why lemurs in deciduous forests have more nocturnal activity than those in rainforests during the winter.

Population size doesn’t explain why the lemur population in the deciduous forest has more nocturnal activity in the winter than the lemur population in the rainforest. We need a factor that affects the lemurs differently based on the tree canopy cover of their environments.

Why would eating only plants cause the lemurs in the deciduous forest to have more nocturnal activity in the winter? We still need a factor that affects the lemurs’ winter behavior differently based on the tree canopy cover of their environments.