How does the shape of a receptor (protein receptor) affect it's function? Describe what happens if a signal molecule fits into the receptor vs if it does not fit.

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?