Deme Q maintained a population of 8940 until there was a shift 641.0 generations ago that reduced its numbers to 5046, a figure that has remained the same since.
time_units: generations
demes:
  - name: Q
    start_time: .inf
    epochs:
      - start_size: 8940
        end_time: 641.0
      - start_size: 5046
        end_time: 0