The population of deme R held at 3758 until 4709.481 generations back, when it changed reaching 7077, which has been constant since then.
time_units: generations
demes:
  - name: R
    start_time: .inf
    epochs:
      - start_size: 3758
        end_time: 4709.481
      - start_size: 7077
        end_time: 0