Until 8001.462 generations ago, the population of deme D was 6881. At that point, it changed to 3616, where it has stayed up to now.
time_units: generations
demes:
  - name: D
    start_time: .inf
    epochs:
      - start_size: 6881
        end_time: 8001.462
      - start_size: 3616
        end_time: 0