Deme Z maintained a population of 5986 until there was a shift 4885.0 generations ago that changed its numbers to 8757, a figure that has remained the same since.
time_units: generations
demes:
  - name: Z
    start_time: .inf
    epochs:
      - start_size: 5986
        end_time: 4885.0
      - start_size: 8757
        end_time: 0