Sometimes, when people set up a terrarium they wish to create a "mini ecosystem" and add a mix of species that will co-habitate in the terrarium. While in theory this sounds like a good idea, it is a situation fraught with difficulties and can only be achieved with a great deal of research and work. For the average keeper of reptiles and amphibians, it is not something I would recommend. Here is why:
- Different species have different requirements, even if the differences seem quite minor. In the wild, each species occupies a unique niche even within the same general climate, where temperature, light, and humidity vary depending on the specific habitat of each species (e.g. tree vs ground dwelling, terrestrial vs. aquatic). In an unnatural situation (the terrarium), it is hard to provide an environment that closely duplicates the natural environment needed to keep single species healthy and stress-free. Providing natural conditions for multiple species is extremely complicated, even if they originate from the same area.
- Terrariums for mixed species generally need to be much larger than those for a single species, and are more difficult to maintain. Extra room is needed to provide the proper environmental conditions and furnishings for each species, as well as allowing each species their own space to hunt and interact somewhat naturally. Crowding different species together in a small tank can be a recipe for disaster.
- Carnivorous critters are usually not picky eaters, and will try to eat smaller cagemates of any species. This still applies to animals (lizards, frogs, salamanders) that are largely insectivorous; most of these will not hesitate to hunt other small animals given the opportunity especially if confined in a tank with them. Also consider the stress you place on an animal, confining it in close quarters with a potential predator.
- Toxicity may be an issue with some frogs, salamanders, and newts. Many secrete mild skin toxins. These toxins may not be dangerous to humans, but they can accumulate in a tank and cause problems if absorbed through the skin of other tank inhabitants or if a cagemate tries to eat a toxic amphibian.
- Animals may become stressed by behaviors and displays that are unexpected and that they do no know how to interpret. Between species that do not normally coexist, normal behaviors and benign displays may be misinterpreted, and this may lead to fighting or stress.
- Animals from different areas or habitats have differing immunities to parasites and infectious diseases. Therefore, one species may harbor a bug that it can carry with no ill-effects. However, if that bug (be it a parasite, virus or bacteria) is introduced to a species with no natural immunity, the result can be devastating.
I know there are people out there that have mixed tanks that seem to do just fine, but my recommendation is to stick to one species per tank. The results of mixing species of reptile and amphibian in a terrarium are unpredictable, especially for less experienced keepers. Providing the proper environment and alleviating stress are too important to the health and well-being of reptiles and amphibians to take chances with mixing species.