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.

Inter-population differences in the tolerance of a marsupial folivore to plant secondary metabolites

“…Interpopulation diVerences in the ability of browsers to cope with PSMs may have important ecological and evolutionary implications, inXuencing factors such as habitat selection, dispersal and gene Xow (Mangione et al 2000), as well as the distribution and abundance of species. McEachern et al (2006) suggested that the lack of dispersal of woodrats across habitat boundaries may be a consequence of local dietary specialization in relation to chemical defences. Similarly, coppery and common brushtail possums may be isolated across the rainforest-eucalypt boundary in northern Australia, which could inXuence population structure.…”

“…Little). Subsequently, McEachern et al (2006) reported specialization by woodrats on local species of plants, which they concluded was a result of avoidance of novel chemical compounds. Among the marsupial folivores, common brushtail possums (Trichosurus vulpecula Kerr) in Western Australia are much more resistant to naturally occurring Xuoroacetate than are their counterparts in eastern Australia, where the occurrence of Xuoroacetate in plants is much lower (Twigg and King 1991).…”

Role of early experience in the development of preference for low-quality food in sheep

“…In previous studies, goats (Distel and Provenza, 1991) and sheep (Distel et al, 1994) early exposed to lowquality forages subsequently showed increased preference for that type of forage. In these earlier studies, lambs and goats experienced the low-quality forage in a poor nutritional context, and the effects of early experience were associated to changes in physiological processes, which increased the animals' capacity to digest fiber, to recycle nitrogen or to detoxify toxins (see also McEachern et al, 2006). Contrarily, in this study, EL experienced LQF in a rich nutritional context and early experience treatments did not affect digestive capacity or nitrogen utilization, probably due to similar nutrient intake in EL and IL during exposure.…”

Scale dependent effects of native prey diversity, prey biomass and natural disturbance on the invasion success of an exotic predator

“…We suggest that prey diversity may not have been a significant predictor of invasion success at either fine or broad scales because of the omnivorous nature and broad diet of signal crayfish (Nyström 2002). Although generalist predators do often show preferences for particular prey, they also readily exploit alternative prey when a preferred prey becomes rare (Bolnick et al 2003;McEachern et al 2006). For example, the invasive ladybird beetle, Coccinella septempunctata, will readily exploit alternative prey in alpha fields, when densities of their preferred aphid prey are low and native ladybirds have already dispersed (Evans 2004).…”