Terpenoid Resin Distribution in Conifer Needles with Implications for Red Tree Vole, <em>Arborimus longicaudus</em>, Foraging

Abstract

Tree voles are dietary specialists, feeding almost exclusively on conifer needles and bark. They reduce their exposure to conifer chemical defenses by physically removing resin ducts from many needles before ingesting the remaining tissue. The portion of needle removed differs among tree species, depending on the location of the resin ducts. To evaluate the amount of resin avoided by this behavior we removed the resin ducts from Douglas-fir, Western Hemlock, and Sitka Spruce needles and used gas chromatography to compare volatile resin concentrations in needles with and without the resin ducts removed. Needle tissues without resin ducts contained no terpenoid resin, demonstrating that tree voles can regulate the nutritional quality of their diet by controlling the amount of resin ingested. We suggest that differences in the physical structure (and possibly chemical composition of terpenes) of the needles make it difficult for voles to easily switch between tree hosts.

Tree voles: an evaluation of their distribution and habitat relationships based on recent and historical studies, habitat models, and vegetation change

“…Another obvious hypothesis is that, in most areas, the upper limits of tree vole distribution could be determined by the upper elevation limits of Douglas-fir, the primary food source of tree voles in most areas. of conifers such as Sitka spruce, western hemlock, grand fir, Monterey pine, and bishop pine in many low-elevation areas (Benson and Borell 1931, Clifton 1960, Jewett 1920, Kelsey et al 2009, Taylor 1915, Vrieze 1980, Wooster and Town 2002, this study). However, there are no records of tree voles feeding on mountain hemlock, Pacific silver fir, or noble fir, and we cannot rule out the possibility that these high-elevation species are unacceptable as a substitute for Douglas-fir as a food source.…”

“…The nest was in a Douglas-fir, but the cuttings and resin ducts in the nest were entirely western hemlock, which the vole had harvested from adjacent western hemlocks that had branches that were in contact with the nest tree. Tree voles that fed on western hemlock and Sitka spruce had to handle needles differently than voles that fed on Douglas-fir (Kelsey et al 2009). When feeding on Douglas-fir, tree voles remove the resin ducts from the outer edges of each needle and eat the middle portion of the needle (Benson and Borell 1931, Kelsey et al 2009, Maser 1966.…”

“…Tree voles that fed on western hemlock and Sitka spruce had to handle needles differently than voles that fed on Douglas-fir (Kelsey et al 2009). When feeding on Douglas-fir, tree voles remove the resin ducts from the outer edges of each needle and eat the middle portion of the needle (Benson and Borell 1931, Kelsey et al 2009, Maser 1966. In contrast, western hemlock has a single resin duct that runs down the center of the needle, and tree voles that feed on western hemlock eat the edges of the needle and discard the center of the needle ( fig.…”

“…The result was an explosion of information regarding many species, including tree voles. Some of this information has been published (e.g., Bellinger et al 2005;Dunk and Hawley 2009;Forsman et al 2004Forsman et al , 2009aForsman et al , 2009bKelsey et al 2009;Swingle and Forsman 2009;Swingle et al 2010), but most of the new empirical information on distribution and habitat of tree voles remains unpublished. Our goal in this report is to summarize the historical and recent information on distribution and habitat of tree voles, and to provide managers with a new tool for assessing potential tree vole habitat.…”

“…Cuttings harvested by tree voles are easily identified based on their small size (typically 8 to 25 cm) and the chisel-shaped bite marks on the base of each twig (Forsman et al 2009b). In addition, cuttings harvested by tree voles are almost always found in association with tree vole fecal pellets, debarked twigs, and discarded resin ducts, which the voles remove from the edges of each needle (Kelsey et al 2009, Maser 1966. In this chapter, we describe and compare diets of tree voles in different parts of their range based on the composition of cuttings found in tree vole nests that we examined in western Oregon and northwestern California in 2000-2013.…”