Until a shift occurred 996.186 generations ago, deme S's population was consistently 1504. Since then, it changed to 7413, a number that has remained unchanged to the current time.
time_units: generations
demes:
  - name: S
    start_time: .inf
    epochs:
      - start_size: 1504
        end_time: 996.186
      - start_size: 7413
        end_time: 0