Watching the film I thought that the rabbit-eared varmints love nature but also probably has a sort of culture or religion of keeping in touch with the environment and keeping it in control. This is because only the varmints survived when the city broke down.
I think in the end nature has destroyed the city not just because it needed to get rid of pollution, but also because the varmints couldn't take care of it in hard labour in the city.
I think that the theme of the story is that we are destroying nature so much that we are killing ourselves and that we have to sacrifice some of our technology to protect nature.
