Until 914.656 generations ago, the population of deme J was 9841. At that point, it changed to 4510, where it has stayed up to now.
time_units: generations
demes:
  - name: J
    start_time: .inf
    epochs:
      - start_size: 9841
        end_time: 914.656
      - start_size: 4510
        end_time: 0