A migration-selection model for the morph frequency variation in the peppered moth over England and Wales

Abstract

A migration-selection model for the spatial and temporal variation of morph frequencies over England and Wales for the peppered moth has been constructed. The morph frequencies have been obtained by computer simulation using the model for various assumptions regarding selection and migration within the boundaries of experimental observation. The selection, in this case, has been assumed to be wholly caused by bird predation and non-visual selection is taken to be same for all phenotypes. The results are compared with available experimental data along three transects. Reasonable agreement with the data is obtained for the Manchester-North Wales transect and the South Wales-London transect. The simulation fails, on the other hand, to reproduce observations along the Central Wales-Birmingham-East Anglia transect. Thus it is concluded that the hypothesis ol balance of selection and migration is untenable as it stands. Either the visual selection pressures are incorrectly or incompletely specified, or else non-visual selection is also operating.