Evidence for local specialization in a generalist mammalian herbivore, Neotoma fuscipes

Abstract

Herbivores with very plastic dietary requirements, or so‐called generalist species, can include individuals that develop specialized feeding habits through their experience with local chemically‐defended plants. Local specialization has important implications for understanding a variety of ecological and evolutionary dynamics. However, the extent to which individuals within a generalist species specialize on local plants and the consequences of such specialization remain poorly understood, especially in non‐insect herbivores. To better understand this phenomenon, we determined the diet and food preferences of a generalist mammalian herbivore, the dusky‐footed woodrat (Neotoma fuscipes), in two adjacent but distinct plant communities. Based on a combination of cafeteria trials and stable isotope analyses (δ13C and δ15N), our results indicate that woodrats display preferences for local plants and tend to avoid novel chemically‐defended plants. Moreover, both methodologies support the conclusion that individual woodrats are dietary specialists restricting their diets to only a few (2‐3) of the available plant species. In juniper woodland, woodrats prefer western juniper (Juniperus occidentalis), while less than one km away in mixed‐coniferous forest, woodrats prefer incense cedar (Calocedrus decurrens). Both plants contain high levels of plant secondary compounds that require detoxification mechanisms within consumers. Therefore, preferences are likely indicative of underlying physiological adaptations that could promote further behavioral, physiological and ultimately genetic differences between woodrats in different habitats. This study provides additional evidence for local specialization and urges caution when using the term generalist to characterize feeding behaviors at the individual level.