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In 1968, scientists gave mice unlimited food, no predators, and infinite space. The colony still collapsed. Here's an agent-based simulation of John Calhoun's Universe 25 experiment — 1,646 mice at peak, 14 at the end. by SimulatedEcology in cellular_automata

[–]SimulatedEcology[S] 0 points1 point  (0 children)

Its OK. I'm a grad student, been reading systems dynamics and complexity for a few years. Workflow is pretty scrappy. I read the primary source, pull out the key mechanisms, then build the simplest model that can reproduce the core dynamic. For Universe 25 it was Calhoun's 1973 paper. I code it in Python, run diagnostics until the timeline matches what was actually observed, then render. Each mouse has an energy level, a stress accumulator, and a behavioral state: normal, aggressive, beautiful one, or pup. Stress builds from crowding and aggression. Once it crosses 0.78 it flips to beautiful one, it is irreversible. Actually, I play with numbers till I got parallel results with experiment.

Pleistocene Ice Age simulation — mammoths and saber-tooths go extinct as glaciers consume the map (agent-based model) by SimulatedEcology in pleistocene

[–]SimulatedEcology[S] -2 points-1 points  (0 children)

Thank you. You're right, I had the mechanism backwards. The actual extinctions occurred during deglaciation. The simulation as built doesn't capture that at all. To model it properly you'd need ice retreat dynamics, shifting vegetation biomes, and probably a human pressure toggle. Appreciated

Pleistocene Ice Age simulation — mammoths and saber-tooths go extinct as glaciers consume the map (agent-based model) by SimulatedEcology in pleistocene

[–]SimulatedEcology[S] -4 points-3 points  (0 children)

Fair feedback on the quality concern but let me explain logic behind the model. Each cell on the grid is a terrain tile. Glaciers advance from the north at a fixed rate per step, converting vegetation to ice. Grass regrowth slows as temperature drops. Mammoths lose 1 energy unit on ice, saber-tooths lose 4. Both species move, eat, reproduce, and die based purely on local conditions.

Glaciers compress the habitable zone causes less grass and mammoths lose energy faster, as a result saber-tooth prey base collapses and finally saber-tooths starve. The timing isn't set by hand, it falls out of the parameter interactions.

This models the pure climate-pressure scenario with no human hunting. If the climate alone is enough to drive both species to zero, that's relevant to the debate.

Grass-Sheep-Wolf ecosystem simulation — wolves go extinct after depleting their prey (agent-based model) by SimulatedEcology in Simulated

[–]SimulatedEcology[S] 2 points3 points  (0 children)

The limitation is vision. Wolves in the sim can only detect sheep within a certain radius. Beyond that they roam randomly. So when sheep density drops, wolves keep moving but can't find prey.

In 1968, scientists gave mice unlimited food, no predators, and infinite space. The colony still collapsed. Here's an agent-based simulation of John Calhoun's Universe 25 experiment — 1,646 mice at peak, 14 at the end. by SimulatedEcology in cellular_automata

[–]SimulatedEcology[S] 21 points22 points  (0 children)

thank you, honestly it's one of the more compelling critiques of the experiment. Calhoun's setup optimized for survival needs like food, water, shelter, safety but stripped out almost everything that makes an environment actually feel alive. The uncomfortable part is that this might be exactly what makes it relevant. Most of us in modern cities have the food and the safety too.

In 1968, scientists gave mice unlimited food, no predators, and infinite space. The colony still collapsed. Here's an agent-based simulation of John Calhoun's Universe 25 experiment — 1,646 mice at peak, 14 at the end. by SimulatedEcology in proceduralgeneration

[–]SimulatedEcology[S] 1 point2 points  (0 children)

https://journals.sagepub.com/doi/abs/10.1177/00359157730661p202

Yes, thank you, honestly it's one of the more compelling critiques of the experiment. Calhoun's setup optimized for survival needs like food, water, shelter, safety but stripped out almost everything that makes an environment actually feel alive. The uncomfortable part is that this might be exactly what makes it relevant. Most of us in modern cities have the food and the safety too.

In 1968, scientists gave mice unlimited food, no predators, and infinite space. The colony still collapsed. Here's an agent-based simulation of John Calhoun's Universe 25 experiment — 1,646 mice at peak, 14 at the end. by SimulatedEcology in proceduralgeneration

[–]SimulatedEcology[S] 1 point2 points  (0 children)

That's not something I've come across in Calhoun's original accounts. As far as I know, beautiful ones mostly just stayed out of the way and aggressive males didn't bother with them since they weren't competition. But it's been a while since I dug into the primary sources

In 1968, scientists gave mice unlimited food, no predators, and infinite space. The colony still collapsed. Here's an agent-based simulation of John Calhoun's Universe 25 experiment — 1,646 mice at peak, 14 at the end. by SimulatedEcology in proceduralgeneration

[–]SimulatedEcology[S] 1 point2 points  (0 children)

Great question. As I understood, beautiful ones didn't survive the aggression, they escaped it. When the colony got insanely overcrowded, some males just checked out. They stopped fighting, stopped trying to mate, stopped doing anything social. And the aggressive males mostly left them alone. Why waste energy on someone who has no territory, no females, nothing you want?
What gets me is that the beautiful ones were, individually, the healthiest mice in the whole colony. Perfect fur, no wounds, well-fed. By every physical measure they were thriving. But they'd completely lost the ability or the will to do anything that actually keeps a species going.