RAPTOR PELLETS OF THE ARCTIC NATIONAL WILDLIFE REFUGE REVEAL SPATIAL GRADIENT IN SMALL MAMMAL COMMUNITIES

Historical and subfossil skeletal remains provide important resources for evaluating extant small mammal diversity. Owls (Strigiformes), many hawks (Accipitridae), and ravens (Corvidae) have the ability to consume prey whole, and regurgitate pellets of indigestible bones and remaining tissues. Resulting pellet accumulations faithfully record local prey diversity because these birds feed largely indiscriminately. Here, we use pellet-derived bone accumulations to evaluate changes in rodent communities across the Coastal Plain of the Arctic National Wildlife Refuge, Alaska. This region is dominated by three microtine rodents; collared lemming (Dicrostonyx groenlandicus), North American brown lemming (Lemmus trimucronatus), and tundra vole (Microtus oeconomus), but there are limited data on how their populations change across space. Furthermore, because pellets can accumulate across decades or more, they may be particularly useful for establishing long-term population metrics for microtine rodents and other species that undergo large population boom and bust cycles. Pellets were collected during taphonomic surveys of openly vegetated tundra habitats (Dryas terraces) near seven major river systems (Canning, Katakturuk, Hulahula, Jago, Aichillik, Kongakut, and Turner Rivers). Rivers flow south-north, bisecting the Coastal Plain at semi-regular intervals across 200 km. Mammalian remains were dissected from pellets and identified based on tooth morphology. Pellets and local bone accumulations were summarized by the minimum number of individuals for each species. We find significant changes in microtine community composition across the Coastal Plain. The community is strongly dominated by lemmings (Dicrostonyx + Lemmus) in the west and voles (Microtus) in the east. The shift in arcsine-transformed proportional abundance of voles is roughly continuous across longitude and is highly significant (weighted linear regression; p < 0.01, R² = 0.75). This dramatic shift in the Coastal Plain microtine species was previously unrecognized. Our results illustrate that (i) even in species-poor tundra settings, biological heterogeneity can be high, and (ii) conservation paleobiology can provide novel insights relevant to understanding cryptic diversity changes in modern ecosystem.