Unfamiliar with the Mouse-Experiment? Read here...

https://scienceinsights.org/is-universe-25-true-what-it-proves-and-what-it-doesnt/

I actually have a two-storey ferret-cage where I had kept a couple of mice at some point in the past...

Reading through the article and learning about how the «size» of their «enclosure» was ONLY a SMALL 9ｘ9 foot square-space automatically made me think that such a space was actually TOO SMALL for a full entire mouse-population civilisation... additionally, I have not seen any evidence that the mice even had anything such as running wheels, a very important «toy» for them...

https://aeius.etqis.com/hub/a-h/apt-unit/a-h/front/

Seeing them run on the running wheels or hearing them if it was a squeaky running wheel is really quite a joy and I have seen that they will share running on the same running wheel with each other if it is the only running wheel available to them, but, if there is only one running wheel and not enough space within the wheel for all of the mice to be able to share their exercising together, well, they might «compete» for the resource to be able to get to run on the running wheel, although I only had a maximum of two mice at a time so that is not something I can say is an absolute-certainty.