Seasonal resource acquisition strategies of a facultative specialist herbivore at the edge of its range

Abstract

Understanding animal performance at range edges has gained increasing interest due to climate change, but most efforts have focused on specialist species. Studying the breadth and plasticity of generalist resource acquisition strategies will provide important insight into how mammals adapt to and persist under a variety of environmental conditions. The North American porcupine (Erethizon dorsatum) is a widely distributed generalist herbivore with special adaptations to harsh climates and low-quality diets. However, on the north coast of California, which has a mild climate and abundant vegetation, porcupine populations are patchily distributed and may be in decline. We studied seasonal resource use of porcupines in a coastal dune ecosystem by measuring changes in body mass, home range size, habitat selection, and diet. Both female and male porcupines lost body mass between summer and winter (X= 8.3% and 17.2%, respectively), although less than reported elsewhere. Their home range sizes were 31% larger during summer than winter. Porcupines selected swales and marshes during the summer, when they fed primarily on willow leaves, and switched to conifer forests and coastal scrub during winter, when they fed on bark, conifer needles, and leaves of evergreen shrubs. Porcupines exploited 2 novel food sources common in Pacific coastal lowlands: coast manroot fruits and California wax myrtle leaves. We suggest that porcupines employ a similarly flexible resource acquisition strategy across their range, and although it appears to be broadly effective, they may face challenges from plant phenology, low broad-leaved tree diversity, and high winter precipitation in Pacific coastal climates.