PS 13-129 - Local to continental-scale small mammal population dynamics in North America

Background/Question/Methods

Small mammal populations are influenced by several factors, including food availability, predation, and climate. It is well known that seed-eating small mammals respond to resource-pulses from mast-seeding (the highly synchronous and variable production of seeds in a population of perennial plants) at local scales with demographic, behavioral, and physiological changes. Recently, an East-West mast-seeding ecological dipole characterized by patterns of opposite extremes in seed production in geographically distinct tree populations has been uncovered across North America, with patterns influenced by climatic dipoles. Because mast-seeding influences small mammal populations, our objective was to test for the existence of an ecological dipole in small mammal population dynamics operating at a scale similar to the masting dipole in North America. To do so, we used small mammal box-trapping records from 2013-2021 for eight seed-eating small mammal species from 20 National Ecological Observatory Network (NEON) sites in the contiguous United States. For each year, we calculated the number of unique individuals captured per species. These NEON sites span distances of > 4,000 km, and we used spatial correlogram analysis to reveal levels of synchrony in temporal patterns among pairs of sites.

Results/Conclusions

Spatial correlograms across all years revealed an ecological dipole in small mammals in North America. Small mammal populations at sites < 600 km apart were significantly positively correlated (synchronized), and this correlation declined with distance and was significantly negative at sites > 2,000 km apart. This pattern is characteristic of an ecological dipole, and reflects a similar scale of pattern to that seen in mast seeding of trees. We predict that the existence of this small mammal ecological dipole may cascade across trophic levels. Our results suggest that the concept of ecological dipoles can be used to predict wildlife dynamics at regional to continental scales in North America. Our analysis of small mammal populations also contributes more broadly to the field of ecology by examining population trends (which tend to be examined at the local to regional scale) across continental scales.