Answer:
The isopods will be found under the leaf litter.
Explanation:
Isopods are crustaceans and they live in freshwater, marine water or on land. The forms of isopods that are found on land mostly prefer the cool and moist environment.
As the biologist will leave them on leaf litter, they will crawl to the area under the leaf because the area under the leaf litter is relatively cool and moist and there they can get an environment which is suitable for their living. Thus when the biologist will come after one hour, most of the isopods will be found under the leaf litter.