Deme O maintained a population of 7220 until there was a shift 6533.76 generations ago that decreased its numbers to 4186, a figure that has remained the same since.
time_units: generations
demes:
  - name: O
    start_time: .inf
    epochs:
      - start_size: 7220
        end_time: 6533.76
      - start_size: 4186
        end_time: 0