Up until 7521.0 generations ago, the count of J deme was 9147. Following that period, it changed to 7518, where it has persisted until now.
time_units: generations
demes:
  - name: J
    start_time: .inf
    epochs:
      - start_size: 9147
        end_time: 7521.0
      - start_size: 7518
        end_time: 0