The population of deme R held at 450 until 7061.404 generations back, when it changed reaching 3686, which has been constant since then.
time_units: generations
demes:
  - name: R
    start_time: .inf
    epochs:
      - start_size: 450
        end_time: 7061.404
      - start_size: 3686
        end_time: 0