Keystone

A living predator–prey valley where nothing is scripted. Eight species — snowshoe hare, elk, beaver, red fox, coyote, gray wolf, cougar and raven — are simulated one animal at a time, each with a body mass, an energy budget, senses, a territory, heritable traits and a cause of death. Population curves are an output, not a setting: they rise and crash because individual animals ate, starved, bred or were eaten. Compose the community yourself and find out what depended on what. Take the wolves out and watch the coyotes boom and the foxes vanish; take the beavers out and watch the wetland itself disappear — the difference between an apex predator and a keystone species, shown rather than stated. Follow one named animal through its whole life and read its story. Overlay your run on the real Hudson's Bay lynx–hare records, watch natural selection move a trait histogram in twenty minutes, export the whole run to CSV, and take a twenty-question Field Exam that tells you exactly where in the simulation to go and look.