Self-Sustaining Ecosystems

A self-sustaining ecosystem is a system that is able to sustain itself without any external support. Benson's aquarium ecosystem is not self-sustaining because he requires his dear, sweet mommy's support to feed him, clean his tank, make sure his water levels are in check, etc. This is due to the fact that Benson's ecosystem is enclosed within the confines of his tank, so he has to eat, sleep, play, blow bubbles, and do his (waste-excreting) thing within one tiny space. In order for his ecosystem to be self-sustaining, the boundaries of his tank would have to be eliminated, and there would have to be food readily available for him (pellets don't spawn in the wild).

Lakes, rivers, and ponds are self-sustaining.

Aquariums are not.