全球变化知识资源中心

Many species that occupy high latitudes of North America were historically restricted to relatively small refugia during the Last Glacial Maximum (LGM). The geographic ranges of many of these species then expanded widely across the continent after glacial ice receded. In contrast, species whose LGM distributions spanned lower (relatively ice-free) latitudes may have been less likely to experience demographic and geographic retraction during glacial periods, or expansion during interglacial periods. For example, species in North America's Intermountain West occupied a topographically complex landscape across which widespread patches of suitable habitat could have helped maintain a relatively stable range-wide effective population size even if local populations fluctuated in response to shifting climates. We test for these alternative demographic signals in southern versus northern species by comparing patterns of genetic diversity of the more southern yellow-bellied marmot (Marmota flaviventris) with those of the more northern hoary marmot (M. caligata). Our data reveal high diversity but no deep structure across the distribution of yellow-bellied marmots. In contrast, hoary marmots have previously been shown to exhibit a deep divergence between regional mitochondrial clades of relatively low diversity. We suggest that these differences reflect differences in habitat availability through time, with hoary marmots persistently isolated in small glacial refugia and yellow-bellied marmots more broadly distributed across the Intermountain West through both glacial and interglacial periods. Our results highlight the importance of historical patterns of habitat availability as key drivers of current genetic structure.