What causes the phytoplankton to shift from their usual rhythm?

The deserts of the sahara and australia are associated with

Idon’t know the answer and i’ve been stuck on it for a while now skskskskks

An ecologist studied the same species of deer during the summer and the winter. she noticed that during the summer, when there was plenty of food, the deer were energetic and playful. however, during winter when food was scarce, the deer moved more slowly and did not run unless they needed to escape a predator. which scientific fact is best supported by her observations?