General properties of predictive population models in red grouse (Lagopus lagopus scoticus).

The general properties of an empirical predictive model of population fluctuations in red grouse are discussed. The model incorporates two observed time-lagged relationships between (a) chick production and spring numbers two years earlier, and (b) overwinter survival and numbers in spring one year earlier. The model produced oscillations which were slowly damped with a period of nine years. The addition of randomly-imposed poor breeding sustained the amplitude of oscillations but did not affect the period. Incorporating immigration at low densities reduced the amplitude but preserved the period. Cycle length varied with the model parameters but was generally between 8-10 years. A model with reduced lags of one and zero years could produce shorter cycles of 4-6 years.