As it was pointed out in your previous post about the same topic, cohabitating different species for a project that allows you to pick any topic that you want seems pointless. You have yet to answer any question in either post about what you are trying to prove. What you have shown is that you generally have a disregard for the animals well being, especially since you admitted there is no added benefit for housing them together. How many pink tongue skinks have you owned, that allows you to state with such certainty that they are all really docile or that they would never attack something like a gecko? How many geckos have you owned? How big is this cage that you feel you will be able to create the proper temp gradient for both animals? I really don't see how this is going to end well, and I don't see how you can expect to make a whole project about forcing two animals to cohabitate for a year.
