TEMPORAL ALLOZYME FREQUENCY CHANGES IN DENSITY FLUCTUATING POPULATIONS OF WILLOW GROUSE (LAGOPUS LAGOPUS L.)

The population density of willow grouse (Lagopus lagopus L.) in northern Scandinavia changes in synchrony with the cyclic density variations in populations of microtine rodents. To assess the genetic changes accompanying the variations in population number, allozyme variation was studied at 23 loci in 640 willow grouse, representing four mainland and one island locality sampled during high and low population density. The average heterozygosity (H = 8.3%) and proportion of polymorphic loci (P = 26%) is not lower in willow grouse than in avian species with a more stable demography; the recurrent population density changes do not appear to affect drastically the long term effective population size, presumably because of extensive migration. Significant allele frequency differences were found both between populations and between different density phases. The genetic distance (D; Nei, 1972) was, in about 50% of the cases, larger between two consecutive time periods than between two localities in a certain year. Spatial and temporal allele frequency variation each represented around 3% of the gene diversity. The temporal heterogeneity may be caused by nonrandom sampling of family groups, rather than drift of allele frequencies between generations due to small effective population size, as has been suggested for microtine species.