Many studies determine which habitat components are important to animals and the extent their use may overlap with competitive species. However, such studies are often undertaken after populations are in decline or under interspecific stress. Since habitat selection is not independent of interspecific stress, quantifying an animal's current landscape use could be misleading if the species distribution is suboptimal. We present an alternative approach by modeling the predicted distributions of two sympatric species on the landscape using dietary preferences and prey distribution. We compared the observed habitat use of kit foxes (Vulpes macrotis) and coyotes (Canis latrans) against their predicted distribution. Data included locations of kit foxes and coyotes, carnivore scat transects, and seasonal prey surveys. Although habitats demonstrated heterogeneity with respect to prey resources, only coyotes showed habitat use designed to maximize access to prey. In contrast, kit foxes used habitats which did not align closely with prey resources. Instead, habitat use by kit foxes represented spatial and behavioral strategies designed to minimize spatial overlap with coyotes while maximizing access to resources. Data on the distribution of prey, their dietary importance, and the species-specific disparities between predicted and observed habitat distributions supports a mechanism by which kit fox distribution is derived from intense competitive interactions with coyotes.
Abstract:We examined the ecological and physical characteristics of den sites for 13 adult kit fox (Vulpes macmtis) in westem Utah from December 1998 to February 2001. We also compared current and historical den distribution among habitat types. The number of den sites used was not influenced by home-range size (P = 0.11) or season (P = 0.40), but was influenced by geographical area. Home-range size was smallest (P = 0.007) and the number of dens used was greatest (P = 0.009) in mountainous areas. Ecological and physical characteristics of single-use dens (n = 30) were compared with those of multiple-use (n = 53) and natal dens (n = 8). Characteristics that differed between den types included number of entrances (P = 0,0001). diameter of entrances (P = 0.003), and height of vegetation along transects ( P = 0.0001). Natal den entrance azimuths were weighted towards a northwesterly aspect ( P = 0.0022); however, single-and multipleuse den exits appeared to be randomly distributed. Historical changes in kit fox den site selection have occurred since 1959 (P < 0.0001). We characterized more dens in invasive grasslands and fewer in greasewood (Sarcobarus vermiculatus) habitats than previously described. The conversion of native habitat to grassland and the increase in coyote population may have altered kit fox distribution to include mountainous areas not previously described.Resume : Nous avons etudie les caracteristiques ecologiques et physiques des sites occupCs par les terriers de 13 renards nains (Vulpe.7 rnacrotis) adultes dans I'ouest de I'Utah, de decembre I998 a fevrier 2001. Nous avons tgalement compart la rtpartition actuelle des terriers en fonction des divers habitats 2 leur repartition dans le passe. Le nombre de sites occupes par des terriers n'est pas influence par la taille du domaine vital (P = 0.1 1). ni par la saison (P = 0.40). mais plutdt par la region geographique. C'est en zone montagneuse que nous avons trouve les domaines les plus restreints (P = 0,007) et le nombre de temers occupes le plus grand ( P = 0,009). Les caracteristiques ecologiques et physiques des terriers occupis une seule fois (n = 30) ont CtC comparies B celles des terriers utilists a plusieurs reprises (n = 53) et a celles des temers natals (n = 8). Les sites varient par le nombre (P = 0,0001) et le diametre (P = 0,003) des entrees et par la hauteur de la dgetation le long de transects ( P = 0,0001). Les azimuts de I'entree d'un terrier natal ont tendance 2 s'orienter vers le nord-ouest ( P = 0,0022); cependant, les sorties des temers a utilisation unique ou multiple semblent reparties aMatoirement. Depuis 1959, les renards on1 modifit leur choix d'habitat pour etablir leur terrier ( P < 0,0001). Nous awns trouve plus de nids dans les prairies herbeuses qui envahissent la region et moins dans les zones de sarcobates vermiculCs (Sarcobarus vermiculatus) qu'auparavant. Ce son1 probablement la conversion de I'habitat indigene en terrain herbeux et I'augmentation de la population de coyotes qui ont Ctendu la repartition des rena...
Resource partitioning between kit foxes (Vulpes macrotis) and coyotes (Canis latrans): a comparison of historical and contemporary dietary overlapUnder conditions leading to coexistence, competition with a dominant species may limit the distribution and density of a subordinate carnivore (Hardin 1960;Schoener 1983; Glen and Dickman 2008;Sidorovich et al. 2010), which can make the population less resilient to changes in habitat or resource availability. Thus, the ability to minimize competition through resource partitioning may be critical for the long-term persistence of specialist carnivore populations facing novel competitive pressures.Resource partitioning is a multidimensional process involving temporal, spatial, and/or dietary shifts in a species' resource use, which lessens niche overlap among species (Schoener 1974; Garneau et al. 2007; Kamler et al. 2012) and reduces negative encounters between were believed to be on increasing and decreasing long-term trajectories, respectively (Arjo et al. 2007). Consequently, we hypothesized we would see an overall decrease in dietary overlap between the two species, reflecting increased competition for prey and, accordingly, an increased degree of dietary resource partitioning. It has been hypothesized that water is a limiting factor in this region (Arjo et al. 2007), and that kit foxes and coyotes select for prey that will maximize water intake (Golightly and Ohmart 1984; Kozlowski et al. 2012). We predicted that coyotes would limit kit fox access to higher-quality dietary prey, such as leporids, which contain higher water content per capture than smaller mammals, such as kangaroo rats (species of genus Dipodomys Gray, 1841) and other rodents (species of the order Rodentia Bowdich, 1821), and non-mammalian prey (e.g., insects, reptiles, birds-Pond 1978). We predicted that kit foxes would respond by increasing their use of small mammals and non-mammalian prey. Materials and methods Study areaThis study was conducted in the Great Basin Desert of western Utah. Sampling occurred on the U.S Army's Dugway Proving Ground and surrounding federal lands managed by the U.S. Dietary overlap was calculated using the Morisita-Horn Similarity Index (hereafter, M-H Index-Horn 1966), in which overlap was based on the proportion of prey classes in the diet, and was measured on a scale of 0 (no dietary overlap) to 1 (complete dietary overlap). All 11 dietary classes were included in measurements of overlap and diversity. Seasonal and annual dietary overlap was assessed within each canid species between the contemporary and historical periods.Dietary overlap was also assessed between kit foxes and coyotes for the contemporary sampling period. Breadth of dietary diversity for contemporary samples was calculated using the ShannonWeiner Diversity Index (hereafter, H'-Shannon 1948). Dietary diversity was measured both annually and for winter and summer sampling periods, and differences in diversity were tested for significance using Hutcheson's t-test (Hutcheson 1970). Differences in...
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