The number of individuals in deme Y remained at 3739 until 309.917 generations ago, at which time it changed to a new stable size of 5876.
time_units: generations
demes:
  - name: Y
    start_time: .inf
    epochs:
      - start_size: 3739
        end_time: 309.917
      - start_size: 5876
        end_time: 0