I agree in some respects with Derek, but you can mix... especially if you aren't breeding (and do not allow it, destroying eggs & hybrid offspring if needed). I also would steer away from the day geckos, but I don't know a whole lot about them. I could see the larger ones grabing a thumbnail dart without hesitation, but not too sure about the smaller ones. Also, I thought that they need a basking area like Derek said... but maybe someone with experience with these will speak up. As for mixing dart frog species, mixing Dendrobates, Phyllobates, and Epidobates is the easiest way to not even worry about hybrids. D. imitator is a very aboreal frog (mine almost never go on the ground) so I think that would be an ok fog to mix with a more terrestrial that won't take larger food items (like terribilis). I would think you could mix imitators with azureus, tincs, auratus, galacts, leucs, and then of course you could mix with some form of the smaller Epidobates. Of course I would also consider pumilio with auratus or vittatus... as I believe they coexist in nature (correct me if I am wrong), so that would be a good natural mix. Of course, I would only mix if you have experience with each individual species first. That way you will be able to plan a better tank for both species, which should lead knock out some of the problem asociated with mixing.