For deme U, the population count was 540 until a change 8003.38 generations ago, where it grew to 9759, remaining steady thereafter.
time_units: generations
demes:
  - name: U
    start_time: .inf
    epochs:
      - start_size: 540
        end_time: 8003.38
      - start_size: 9759
        end_time: 0