Deme Y maintained a population of 9654 until there was a shift 6375.0 generations ago that changed its numbers to 7315, a figure that has remained the same since.
time_units: generations
demes:
  - name: Y
    start_time: .inf
    epochs:
      - start_size: 9654
        end_time: 6375.0
      - start_size: 7315
        end_time: 0