Population genetics and habitat selection behaviour of Vancouver Island white-tailed ptarmigan (Lagopus leucura saxatilis).

摘要

I examined the habitat selection behaviour and compared regional variation in population performance of a threatened alpine grouse subspecies, the Vancouver Island white-tailed ptarmigan (Lagopus leucura saxatilis). I also examined the genetic population structure and levels of gene flow among 7 populations of white-tailed ptarmigan on Vancouver Island, British Columbia. Population performance was compared between 2 distinct mountain areas of Vancouver Island. The southern region was a more fragmented landscape with smaller isolated alpine patches compared to the more continuous central region of the island. The habitat selection modelling revealed that, unlike other white-tailed ptarmigan subspecies, Vancouver Island white-tailed ptarmigan use a generalist strategy for habitat selection. Individuals preferred areas with a combination of predator cover, food availability and high moisture. The analysis of population performance showed that populations in the central region of the island outperform southern populations. This difference could result from moisture levels which are lower in the southern portion of the island, but likely is not influenced by food abundance during the brood rearing period. I presented data on microsatellite primer optimization and described generalized heterozygote deficiencies and high levels of diversity in Vancouver Island populations. All 7 populations demonstrated high levels of diversity (mean HE = 0.78) combined with high FIS values (0.22) and significant heterozygote deficiencies. The apparent paradox of high diversity combined with high FIS and generalized heterozygote deficiencies are best explained by two scenarios. First, sampling may have captured a snapshot of a group of populations progressing towards severe isolation. This scenario suggests that significant geographic isolation between populations has existed long enough for the increase of inbreeding but not long enough for drift to result in strong population differentiation and a corresponding decrease in diversity. The second scenario evokes a pattern of infrequent dispersal between populations sufficient to maintain high levels of diversity, combined with low densities and limited mate choice resulting in the relatively quick accumulation of homozygosity levels within populations. I addressed patterns of dispersal using genetic data and direct measures by following the inter-seasonal movements of radio-collared birds. The results showed low, but significant, genetic differentiation between most populations and direct and genetic estimates of dispersal suggested limited gene flow among populations. Analysis of molecular data also demonstrated a generally consistent pattern of isolation-by-distance. However, large areas of unsuitable low elevation habitat might act as barriers to gene flow. The levels of isolation and lack of gene flow imply serious conservation concern for the most southern population.