Answer: A drought has impacted the population size of the frogs.
Step-by-step explanation:
The frogs are the amphibians who require both water and terrestrial habitats to survive and reproduce. The rainwater accumulates over the terrestrial regions can provide an ideal environment for the survival of the frogs.
According to the given situation, Carter noticed hundreds of frogs on the road after rain storm as the road environment was suitable for the survival of the frogs. But later on he observed less than four or five frogs. This may be because of the fact that the road might not be left with water which could be probably due to drought (a drought is a condition where a region does not receive appropriate amounts of rainfall which leads to the dry and hot environment).