Biotic factors influencing the unexpected distribution of a Humboldt marten (Martes caurina humboldtensis) population in a young coastal forest

Abstract

Pacific martens ( Martes caurina ) are often associated with mature forests with complex structure for denning, resting, and efficient hunting. Nonetheless, a small isolated population of the Humboldt subspecies of Pacific martens ( Martes caurina humboldtensis ) occupies a narrow strip of young, coastal forest (< 70 years old) but not inland mature forest in the central Oregon Coast Range. We examined factors contributing to this unexpected distribution of martens by 1) analyzing marten diets using DNA metabarcoding to assess 90 scats, 2) using camera traps to assess differences in the relative abundances of prey, competitors, and predators across a coastal to inland gradient of vegetation types, and 3) quantifying differences in extent of fruit-producing shrubs and vegetation structure within vegetation types. Diets of martens were diverse (12, 10, and 3 species of birds, mammals, and amphibians respectively), and most fall and winter scats contained fruit. Voles, mice, and varied thrushes ( Ixoreus naevius ) were dominant prey items. Voles, mice, and most birds, but not varied thrushes, were more commonly observed in the coastal shrub-dominated forest than in inland forest. The coastal shrub-dominated forest had the highest diversity of vertebrates and potential prey overall. Bobcats ( Lynx rufus ), a key potential predator, were more commonly detected in inland forest. Of potential competitors, western spotted skunks ( Spilogale gracilis ) were more commonly detected in inland forest, with gray foxes ( Urocyon cinereoargenteus ) and raccoons ( Procyon lotor ) detected almost exclusively in coastal forests. Vegetation in coastal forests appears to provide, at least seasonally, more prey and fruit, and more overhead shrub cover compared with inland forest. Remaining plausible hypotheses for the restricted distribution of marten to coastal forests include increased prey, fruit, and overhead cover, and reduced predation risk from bobcats.

More affordable and effective noninvasive single nucleotide polymorphism genotyping using high‐throughput amplicon sequencing

“…As part of a larger diet study, we used DNA metabarcoding to confirm carnivore species assignment of each scat prior to genotyping. We amplified part of the mitochondrial 12S gene using slightly modified vertebrate primers 12SV5F and 12SV5R used in Eriksson, Moriarty, Linnell, and Levi (2019), adapted from Riaz et al. (2011) (see Supporting Information for detailed methods).…”

More affordable and effective noninvasive SNP genotyping using high-throughput amplicon sequencing

“…As part of a larger diet study, we used DNA metabarcoding to confirm carnivore species assignment of each scat prior to genotyping. We amplified part of the mitochondrial 12S gene using slightly modified vertebrate primers 12SV5F and 12SV5R used in Eriksson, Moriarty, Linnell, and Levi (2019), adapted from Riaz, Shehzad and Viari (2011) (see supplemental material (S1) for detailed methods). Since our 12S primers cannot distinguish between coyote and wolf ( Canis lupus), we included SNPs with wolf-specific alleles in our panel of SNP primers (Monzón, Kays, & Dykhuizen, 2014).…”

Describing vegetation characteristics used by two rare forest-dwelling species: Will established reserves provide for coastal marten in Oregon?

“…Our study locations may be more diverse and have a different management history compared to locations where Humboldt martens were found in northern California [56, 70]. If critical habitat elements were not strongly correlated with vegetation cover, but instead associated with more ephemeral resources such as prey [71] and predation risk [72], then we would predict Humboldt martens to be associated in areas with such biotic elements as much or more than areas with vegetation cover [73]. Understanding the proportional importance of individual habitat elements was beyond the scope of this study, but experimental studies elucidating such information would benefit future management and conservation (e.g., [4]).…”