Place some grass first, then add rabbits. Watch nature unfold.
Ecosystem Builder is a free interactive nature simulation where you create a functioning ecosystem from scratch. Place grass, rabbits, foxes, and hawks on an open field and watch as food chains emerge, populations rise and fall, and natural selection plays out in real time. Your goal: sustain all species for 5 minutes.
Every organism runs on energy. Grass grows by absorbing sunlight and spreads slowly. Rabbits eat grass to gain energy and flee from predators. Foxes and hawks hunt rabbits — foxes on the ground, hawks from above. When an organism's energy exceeds 80%, it reproduces. When energy hits zero, it dies. The balance between producers and consumers determines whether your ecosystem thrives or collapses.
An ecosystem is a community of living organisms interacting with each other and their physical environment. It includes producers (like grass), consumers (like rabbits and foxes), and decomposers, all connected through food chains and energy flows. In Ecosystem Builder, you construct these relationships by placing organisms and observing how they interact.
Ecosystems collapse when critical balances are disrupted. Removing a keystone species, overpopulation of one species, or resource depletion can trigger cascading failures. In this simulation, placing too many predators without enough prey — or too few producers — will quickly destabilize the system.
A food chain shows how energy flows from one organism to another. In Ecosystem Builder, grass is eaten by rabbits, which are eaten by foxes and hawks. Each trophic level transfers roughly 10% of its energy upward, which is why there are always more producers than top predators in a healthy ecosystem.