Bias in carnivore diet analysis resulting from misclassification of predator scats based on field identification

Abstract

Diet studies are frequently used to improve understanding of predator ecology, potential effects of carnivores on prey populations, and competition among predators. However, field identification of carnivore scat typically relies on scat morphology, size, and contents resulting in possible subjective predator identification and potentially biased results. Advancements in noninvasive genetic sampling allow for molecular identification of predator scat, eliminating many issues associated with field identification methods. We collected scat samples once per month from June 2011 to May 2012 in western Virginia, USA, using morphological characteristics for field identification of the predator. We then used mitochondrial DNA to identify the predator species of each scat and identified prey remains visually. Using confusion matrices, we found a range of accuracy in field identification for the 3 target species: coyotes (Canis latrans; 54.0%), bobcats (Lynx rufus; 57.1%), and black bears (Ursus americanus; 95.2%), even though we only considered samples with high-confidence field identification. We found a high coyote false-positive rate (52.7%), indicating we often incorrectly identified scats as coyote (98% of misidentified bobcat scats and 75% of misidentified black bear scats were recorded as coyote in the field). This asymmetrical bias in predator identification resulted in inaccurate estimates of dietary niche breadth and overlap between competitors. Our results suggest that caution should be exercised when interpreting results from studies in which carnivore species are identified by scat morphology. Future studies should employ noninvasive genetic sampling for carnivore scat identification, especially in areas with sympatric predator species that have similar scat morphology. Ó 2016 The Wildlife Society.

Space use and resource selection of bobcats in the Appalachian Mountains of western Virginia

“…Male bobcats also exhibited 2 nd order selection for deciduous forest only during the dispersal season, which overlaps with the peak of hard mast production. Squirrels are the most common diet item of bobcats in this study area [8], and both gray squirrels ( Sciurus carilonensis) and fox squirrels ( Sciurus niger) exhibit peaks in foraging behavior during this time [56,57,58].…”

“…and cougars ( Puma concolor ) remain extirpated from ecosystems in the Appalachian Mountains, leaving bobcats as an apex predator in the region, along with black bears ( Ursus americanus ) and coyotes ( Canis latrans ) [8]. Within this guild, bobcats are the only obligate carnivore, can occur at population densities approximately twice that of coyotes [9,10], and consume a diversity of taxa [8]. Thus, bobcats hold potential to influence populations of both prey and competitors, and understanding the spatial ecology of bobcats may be important to predicting spatial variation in top-down forces in these systems.…”

Apex predators and the facilitation of resource partitioning among mesopredators

“…All carnivore scats that were encountered were collected, and we used mitochondrial DNA to confirm the field identification of each scat. Samples that failed to amplify for molecular identification were excluded from further analyses to minimize potential bias in diet analyses associated with field identified scats (Morin et al 2016). Fecal samples were scraped with sterilized wooden craft sticks, and DNA was extracted using the Qiagen QIAamp DNA Investigator Kit.…”

Winter habitat associations of eastern spotted skunks in Virginia

“…At the highest elevations, small amounts of northern hardwood‐montane boreal forest dominated by yellow birch ( Betula alleghaniensis ), sugar maple, American beech, and red spruce were present (Braun , Simon , ). Common mammalian fauna in the study area include American black bear ( Ursus americanus ), bobcat, coyote, eastern chipmunck ( Tamias stiatus ), gray fox ( Urocyon cinereoargenteus ), gray squirrel ( Sciurus carolinensus ), raccoon, red fox ( Vulpes vulpes ), striped skunks, Virginia opossum ( Didelphis virginiana ), and white‐tailed deer ( Odocoileus virginianus ; Morin et al ).…”