Final answer:
Terrariums are self-sufficient ecosystems that do not require external resources like water and air to survive due to the water-conserving adaptations of their plants.
Step-by-step explanation:
Terrariums are self-sufficient ecosystems, because they do not need to bring resources such as water or air in from the outside environment to survive. Terrariums create a closed environment where plants can recycle moisture through the processes of transpiration and condensation. The plants in terrariums are often those that have adapted to conserve water, such as those with fleshy leaves, waxy cuticles, and sunken stomata to reduce transpiration. These adaptations allow the plants in terrariums to thrive with minimal external resources, making the entire system largely self-sustaining.