It was necessary in Dr. Losos experiment that the experimental islands lacked lizards because the isolation of each ecomorph was vital to make it easier to observe and study. The lack of the lizards allowed for an unhindered observation. The experimental islands were later introduced with the lizards, This experimentation helped in studying the process of adaptation and natural selection.
Hence, the answer is 'it was important that the islands lacked lizards so that the ecomorphs could be easily studied'.