Dispersal and the microtine cycle: comparison of two hypotheses

The hypotheses suggested by Chitty (1960) and by Charnov and Finerty (1980) in order to explain the occurrence of the microtine density cycle are investigated from a theoretical point of view. The former hypothesis assumes that the polymorphic behavioural patterns being observed in natural populations are genetically determined whereas the latter assumes these polymorphic behavioural patterns to be environmentally determined. For both theories we assume a patchy environment with dispersal between patches.We find, on the basis of a series of mathematical models comparing the two hypotheses, that Chitty's hypothesis does not seem to generate cycles whereas the Charnov-Finerty hypothesis may generate persistent density cycles: this is particularly so if dispersing individuals have the capacity to choose which patch to settle in and if the carrying capacity of each patch is high.