Physiological limitations of dietary specialization in herbivorous woodrats (Neotoma spp.)

For nearly three decades, a fundamental objective in the study of plant–herbivore interactions has been to understand why the consumption of a single plant species is rare in mammals, as only a handful of mammalian herbivores (b1%) are dietary specialists. Here, we provide an overview of various factors that may play a role in limiting dietary specialization. We review the energetic consequences of ingesting PSMs and the physiological tradeoffs of specialization in a juniper specialist, Neotoma stephensi, and generalist, N. albigula, woodrat. In general, the energy budgets of specialist and generalist woodrats were negatively impacted by the intake of PSMs from juniper and novel PSMs. However, juniper specialists minimized the energetic costs associated with the intake of juniper through greater energy intake and lower energy expenditure than generalists and thus had more energy for other energy-dependent activities when consuming a juniper diet. Despite the high capacity to consume juniper, juniper specialists experienced a decreased ability to consume novel PSMs, suggesting a dietary trade-off associated with specialization. These data indicate that the energetic consequences of consuming PSMs and the dietary trade-offs associated with specialization may constrain dietary specialization in herbivorous woodrats. Identifying these factors and their role in limiting and/or facilitating dietary specialization in woodrats has provided a better understanding of the foraging ecology, physiology and evolution of mammalian herbivores in general. D 2004 Published by Elsevier B.V.