Here's the opening sentence from the section of the link you're refering to:
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What Other Kinds of Animals Can be Kept With Dart Frogs? [/FONT]
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Generally speaking it's a bad idea to try to keep other animals with dart frogs, in particular if you are a beginner, and if your tank is smaller than about 60 gallons…[/FONT]
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Still sounds like you shouldn't mix them with other herps if you ask me. 
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Dart Frogs require low temperatures in the low to mid 70's. Most lizards they suggest require higher temps and a basking spot which would raise them temperature in the tank and possibly stress and kill the frogs. I'd be afraid too that the other tree frogs listed might eat your dart frogs as well seeing how they now lack their deadly toxin.
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