Prey use by red foxes (Vulpes vulpes) in urban and rural areas of Illinois

Abstract

Decline of red fox (Vulpes vulpes) populations in Illinois has been attributed to altered geographic landscapes and the eastward expansion of the coyote. To investigate effects of habitat use and competition with coyotes on diets of foxes in intensively farmed landscapes of Illinois, we analyzed carbon and nitrogen isotope ratios (δ13C and δ15N) of foxes, coyotes (Canis latrans), and other local species. Foxes were categorized as rural (agricultural habitat, coyotes present), urban (urban habitat, coyotes absent), or from an agricultural research facility at the University of Illinois (South Farms, agricultural habitat, coyotes absent). Rural foxes had higher fur isotopic values (δ13C and δ15N) than rural coyotes, indicating that coyotes caused foxes to consume prey items from higher trophic levels and eat more C4 plants. Urban foxes had lower isotopic values (δ13C and δ15N) than South Farms foxes, suggesting that habitat use partly determined fox diets; foxes in urbanized habitats consumed prey at lower trophic levels within a largely C3 plant based food web. Models of competitive exclusion by coyotes were better predictors of fox long-term diets, including pup rearing, while habitat use models predicted fox diets on a narrower timescale. Competitive exclusion by coyotes might be an important factor explaining the decline of foxes in the intense farming areas of Illinois.

Isotopic investigation of niche partitioning among native carnivores and the non-native coyote (Canis latrans)

“…This ordering of δ 13 C values among the four species is likely due to varying incorporation of the C 4 signal into their respective diets by way of corn (and its derivative, corn syrup, in anthropogenic foods), contrasting with the native flora of the Adirondack region which follows the C 3 photosynthetic pathway [44][45][46]63]. That red fox had the highest δ 13 C values is consistent with dietary studies elsewhere that show anthropogenic foods to be one of the most common items in their diet [10,64,65]. In this study site, anthropogenic foods are likely a supplemental, though not exclusive, source of food for red foxes.…”

“…Although stable isotope analysis has been used to compare individuals within a population, few studies have demonstrated the utility of this technique for comparing resource use and niche overlap among modern mammalian carnivores at the community level (but see [10,59,60]). Hypothesized rankings of species in isotopic niche space formed from a priori expectations and based on habitat use proved a useful way to explore foraging strategies among species.…”

The diet of black bears tracks the human footprint across a rapidly developing landscape

“…More generally, our findings corroborate the utility of δ 13 C as a tracer of human-derived food in temperate North American systems (Hopkins et al, 2014;Lavin et al, 2003;Newsome et al, 2010Newsome et al, , 2015. Carbon-13 enrichment is primarily attributed to high use of corn in human foods (Jahren et al, 2006;Jahren and Kraft, 2008); the similar enrichment of 15 N in human hair is likely due to high meat consumption in North America (Schoeller et al, 1986).…”

“…Newsome et al, 2010). However, isotopic analysis examines assimilated diet, avoiding this bias, and has been successfully used to detect human-derived food consumption in omnivorous mammals including foxes (Lavin et al, 2003;Newsome et al, 2010), coyotes (Garwood et al, 2015;Newsome et al, 2015), and bears (Hobson et al, 2000;Hopkins et al, , 2014Mizukami et al, 2005). For example, Hopkins et al (2014) demonstrated that consumption of human-derived foods by black bears in Yosemite National Park varied temporally with management policies of trash.…”

Variation in collagen stable nitrogen values in black-tailed jackrabbits (Lepus californicus) in relation to small-scale differences in climate, soil, and topography

“…This applies as much or more to studies of diet as it does to paleoclimate. The range of hare values seen here encompasses all herbivores sampled from the Stillwater Marsh in the Lahontan Basin (Schoeninger, 1999) and the majority of the 23 East African taxa reported by Ambrose and DeNiro (1986a); means approach those of higher trophic level carnivores from there and elsewhere (e.g., Lavin et al, 2003). Although one or two samples of a potential resource are infinitely better than none, the value obtained can be very different from the true average.…”