A genetic explanation for ten-year cycles of grouse.

Chitty's Polymorphic Behavioural Hypothesis (Chitty 1967) was logically reduced to three main assumptions that were mathematically modelled: 1) Level of aggression is genetically determined by simple Mendelian selection. 2) Recruitment is inversely related to female parental level of aggression. 3) Aggressives are completely successful in breeding competition. The model utilized data from willow ptarmigan populations, but was generalized to other grouse species. Simulation results were indistinguishable from the behaviour of real world grouse populations lending support to Chitty's hypothesis as the explanation of cyclicity. The model also seems applicable to ther species. Eight tests that would falsify the model were identified.