"Two species of salamander inhabit an island. The habitat on each side of the island is different. One side tends to be wet; the other side tends to be dry. Researchers want to know if the salamanders will survive equally well on either side of the island. Species A lives on the wet side of the island, while Species B lives on the dry side of the island. Researchers develop two artificial habitats, one that simulates conditions on the wet side and one that simulates conditions on the dry side.
Researchers put three salamanders of each species in each of the two different artificial environments. Why would other scientists question the validity of the conclusions based on this setup?"