Picosystems
Some people consider it the holy grail of frogging. A completely self-sustaining terrarium. All you would need to add is light. After all, that's all that is provided in a poison dart frog's natural habitat, right? Well, a terrarium is not a natural habitat. Not even close. This means that a vivarium keeper must provide a number of artificial concessions that are not found in the natural environment. In an ideal world, it would be sufficient to add set up a vivarium, seal it up and then provide light as the only input. In reality though, a completely self-sustaining ecosystem is not practical in a sealed environment such as a terrarium. The goal of this section of the website is to explore the limits of this impracticality. In addition to light, you must also provide fresh air, water to replace what has evaporated, vitamin enriched food for the animals and maybe even fertilizer. The ideal goal of a picosystem is to minimize these inputs.
On this website I use the term "picosystem" to mean a vivarium in which steps have been taken to encourage a degree of self-sufficiency. The impracticality of a truly self sustaining ecosystem inside a terrarium means that what one person means by self-sustaining might be quite different than another person. Therefore to prevent ambiguity, picosystem is operationally defined here to mean...
1) A terrarium in which steps have been taken to allow some microfauna to breed and provide continuous source food for larger animals without continuous introduction of new microfauna.2) The terrarium should be able to survive relatively unaffected if the owner leaves town for a few weeks.
The feasibility of a self-sustaining vivarium
In the strictest definition, the self sustaining system would be in the same vain as Biosphere 2. Only energy is allowed to enter and leave the system. While such a system is theoretically awesome, it is impossible in practicality. First of all, I suspect no one could actually build a gas tight system (and I spend my working day fighting gas gradients). More fundamentally, if a $200,000,000 project was unable to produce enough O2, there is no way a small enclosure is capable of producing a balanced CO2/O2 cycle. The tank would become hypoxic (not enough oxygen) and hypercapnic (to much carbon dioxide) very quickly (and every night).
So, allowing that there will be gas exchange from the system, is it possible to maintain a tank without adding any organic material? Probably not. This would require an incredibly productive ecosystem, with the plants providing enough material for microfauna to eat, and thus producing enough microfauna to feed the frogs. Brent Brock has termed this an allochthonous vivarium, and he has written an excellent post on frognet about why this is so impossible (or most correctly, really, really hard), which can be found here.
Essentially, every rung your move up in the food chain requires 10x more organic matter. This point is possible, but then you must have the correct diversity of microfauna to funnel the plant matter into the frogs, and break down the plants enough to feed the frogs, but not enough to exterminate the frogs. Such a system would probably suffer some severe crashes, extincting some important species (including the frogs).
The two examples that really stand out to me as accomplishments are both "compostiums". Matthew Mirabello has an interesting thread on frognet about a tank he set up with plenty of microfauna, and only occasionally adds kitchen scraps to it, which can be found here. He had success by letting the microfauna build up for over a month and then adding 6 newly morphed auratus and leaving them alone for a while. The frogs apparently grew really fast.
In my opinion, the coolest compostium was built by Ben Eiben, and the thread can be found here. Apparently I'm not the only one awe inpired by this, as the thread has remained active for 3 years, and spawned a few frognet threads. What Ben did, was to split his tank in half with a sheet of tree fern. Half of the tank was a beautiful display of life, the other half was a beautiful display of death, AKA a compost bin. He would add to the compost half, and the microfauna were capable of freely moving between sides. This could also be considered a refugia or refugium. The microfauna that moved to the frogs' side of the tank were eaten, but the refugia assured that they would not be extincted, and provided a constant food supply for the microfauna.
Some people may not want to display a compost bin, especially if it is a display piece in the house, so there has also been discussion of a remote refugia, which would be hidden away, connected to the display setup by a series of tubes. I personally think such a setup would not be as effective as Ben's compostium and might have trouble feeding enough food to the frogs. There are perhaps complex ways to overcome this (ie coaxing the microfauna to the frog tank by making the remote refugia temporarily unpleasent with heat of light), but it is probably not practical. I should note here, that such a tank should not be considered mere;y for its low maintained, as Ben indicated that balancing the compost takes just as much time as feeding, and considerably more effort.
In the remainder of this article gas, water and food are each discussed.
Air
There two main gases which need to be exchanged with the environment, oxygen (O2) and carbon dioxide (CO2). Specifically, oxygen is required by the inhabitants of the terrarium and needs to be exchanged into the terrarium, whereas carbon dioxide can be toxic, even in low doses and needs to be exchanged out of the terrarium. There are also a number of other gases which can cause problems in specific instances, such as ammonia and sulfide
Oxygen might seem like an odd resource to input into a terrarium. After all, plants generate oxygen, right? Yes, plants DO turn water into oxygen, but only in the presence of light. At night, plants actually consume oxygen and generate carbon dioxide. If plants were the only organisms in the terrarium, it might be fine to seal them in. A healthy picosystem, however, has many more organisms than just plants. The bacteria and fungi in the soil together can consume a significant amount of oxygen and produce dangerous levels of carbon dioxide. This is accelerated in warmer environments. Elevated carbon dioxide levels, especially on a warm day can be a death sentence for frog or lizard or even some invertebrates. In there natural environments these organisms could retreat away from the carbon dioxide, but in the terrarium they will be trapped. Carbon dioxide is heavier than air so that CO2 produced in the bottom of the terrarium (such as from microbes in the substrate) will pool at the bottom of the terrarium.[INSERT CARBON DIOXIDE PITS]. Forced air recirculation within the terrarium can help to prevent carbon dioxide pits from forming in the bottom of your terrarium.
Fortunately this is a very easy danger to overcome with a little ventilation. For an overview of the different types of ventilation, please check out the section devoted to ventilation.
Water
Providing enough water for a healthy vivarium is quite simple. With proper ventilation, water evaporation can be minimized and an occasional misting should be sufficient to maintain high humidity. The standing water in the terrarium, whether it is in the false bottom or in a water feature, will accumulate salts and organics over time and should be exchanged on occasion. How frequently it needs to be exchanged will depend on the quality of the water you add to the terrarium, how much the water evaporates and how efficient your plants are at filtering nutrients from the water.
How do you maintain high humidity? Well, there are a number of factors which will influence the humidity of the terrarium. Obviously a major factor is the ventilation. Good ventilation will provide a balance to minimize water loss, but maximize exchange of oxygen and carbon dioxide. Wet surface area and foliage also helps to keep humidity up. A clay or stone background, as well as driftwood, can wick water up from the substrate where is will evaporate and generate increased humidity. Plants can suck up water with their roots and release it into the terrarium through little pores in their leaves called stomata. This means that a terrarium with a porous background and which is full of plants will have higher humidity than the equivalent terrarium with nothing but a puddle of water in the bottom
Running water breaks up surface tension and dramatically increases humidity. In a paludarium this can be accomplished with a airstone in the water section. A more aesthetically pleasing solution is to create a water feature such as a waterfall or a dripwall. See the water feature section for more details. A water feature allows you to increase the ventilation without compromising humidity levels. This allows you to use evaporative cooling to as a refrigerator, slightly lower the temperature of the vivarium. The drawback is that this requires you to add water back to the terrarium more frequently.
A misting system is another solution for elevating humidity. If your terrarium has a drainage system in place, a misting system can altogether alleviate the need for water changes. The misting heads can be run more or less frequently depending on the needs of the inhabitant or to simulate a dry or rainy season.
Food
The food and nutrients needed by the picosystem depend on what animals are in it. In an ideal world you would be able to have fast growing plants which are consumed by fast growing bugs which are consumed by your frogs. This is impracticable, especially without having all of you plants eaten by the bugs.
This means that we need to cheat. Specifically, we need to feed the microfauna in our terrarium organic matter. I have had the best success by seeding the terrarium with multiple species of microfauna such as mites, springtails, woodlice and amphipods. A thick layer of leaf litter provides enough refuge for the microfauna to breed and avoid being immediatley eaten. By occasionally mixing some fish and dog food into the leaf litter you will ensure a booming microfauna population. Once you microfauna have reached high enough population density, you can place some fish or dog food on a piece of driftwood out of the substrate and you will notice it covered in microfauna. Your frogs will also notice the microfauna, and will wait by the food in the morning, anticipating their meal. Have a large microfauna load allows your animals to spend their days hunting instead of anticipating their next meal and I think it results in some more interesting behaviors.
