GOAL: determine if all birds north of the Missouri River in Montana & Canada form a single population or multiple populations.
OVERVIEW: Sage-grouse are endangered in Canada and their range and abundance has declined throughout North America. Over the past 35 years their numbers have decreased by 66%-92% in Canada. In Montana, population numbers have also declined, but there are still regions that are stable. I used 13 microsatellite loci to genotype 2519 individuals from 104 leks in Alberta, Saskatchewan, and Montana. I set out to examine 3 major questions: (1) What is the population structure of the species at the northern edge of its range? Do all birds north of the Missouri River (the proposed Northern Montana population) belong to one or multiple populations? (2) Has habitat fragmentation impacted population structure and genetic diversity by isolating regions and accelerating the population decline? (3) Are birds at the northern periphery (north of the Milk River) genetically depauperate compared to those found in the core (between the Milk and Missouri Rivers)? STRUCTURE identified two populations: (1) the Powder River Basin and (2) Northern Montana (everything north of the Missouri River). The Northern Montana population exhibited significant isolation by distance, with the Milk River area in Montana demarking two subpopulations. Both subpopulations exhibited high heterozygosity and allelic diversity and showed no evidence of peripheral regions, including Canada, being genetically depauperate or highly structured compared to core areas. Analysis of molecular variance revealed that the lek contained the majority of genetic variation. Relatedness based isolation by distance and a structure based assignment test showed that Sage-Grouse in the Northern Montana population are capable of dispersing up to 300 km. Long distance dispersers appear to be able to cross or circumvent current forms of fragmentation and are slowing the effects of disturbance on the population through gene flow. However, most birds are not long distance dispersers so increased fragmentation will likely have a detrimental impact on the population if it continues at its present rate.