Road Density as a Factor in Habitat Selection by Wolves and Other Carnivores in the Great Lakes Region. (Habitat Issues)
Wydeven, Adrian P., Mladenoff, David J., Sickley, Theodore A., Kohn, Bruce E., Thiel, R. P., Hansen, Jennifer L., Endangered Species Update
Although wolves (Canis lupus) and many other carnivores are habitat generalists, certain landscape features can be used to predict suitable habitat. Thiel examined the concept of road density as an important factor in the persistence of wolf populations in Wisconsin prior to the 1960s and found a relationship with the disappearance of breeding wolf populations when average road density exceeded O. 58 km/k[m.sup.2]. Mladenoff and colleagues examined road density in the early 1990s as a factor in predicting favorable habitat of wolves colonizing Wisconsin between 1980 and 1992, and found that areas with road densities less than 0.45 km/k[m.sup.2] had greater than a 50% probability of being colonized by wolf packs. Mladenoff and colleagues updated this work in the late 1990s by examining 23 packs colonizing Wisconsin between 1993 and 1997; 78% continued to occupy areas with road densities below 0.45 km/k[m.sup.2]. In a recent examination of radio-collared wolves in Wisconsin, a total of 60% of human-induced mortality occurred at road densities above 0.63 km/k[m.sup.2]. Although road density may become less of a factor as human tolerance changes, and wolf populations increase, it continues to be an important factor in habitat selection by wolves and probably other carnivores.
Gray wolves (Canis lupus) are generalists in their use of habitat, and historically have been found in most regions across temperate, boreal, and arctic regions of North America (Mech 1995). Despite this generalist nature of habitat use, landscape features, especially those relating to human impacts, can be used to predict suitable wolf habitat (Corsi et al. 1999; Massolo and Meriggi 1998; Mladenoff et al. 1995). Road density has frequently been used as a landscape feature to predict suitable wolf habitat (Corsi et al. 1999; Frair 1999; Fuller et al. 1992; Jensen et al. 1986; Mech et al. 1988; Mladenoff et al. 1995; Thiel 1985).
Early development of concept of road density
As a graduate student under Aldo Leopold, Thompson (1952) studied wolf food habits in northern Wisconsin in the late 1940s, about 10 years before wolves disappeared from the state. Thompson (1952) warned that development and opening of roads across the logged forests of northern Wisconsin could cause wolves to become extirpated from the state. As predicted, wolves were extirpated from Wisconsin by 1960 (Thiel 1985; Wydeven et al. 1995).
Thiel (1985) examined the disappearance of breeding populations of wolves in Wisconsin from 1926 to 1960. Using State Highway Commission Reports, he determined that breeding wolves disappeared from 10 Wisconsin counties after road densities in these counties exceeded 0.48 to 0.68 km/k[m.sup.2] (X = 0.58 km/k[m.sup.2]). The value of 0.6 km/k[m.sup.2] has since been used frequently as the threshold level at which wolf populations can be maintained. This level was found to correspond well with areas of occupied wolf range in Minnesota (Fuller et al. 1992; Mech et al. 1988), Michigan, and Ontario (Buss and Almeida 1998; Jensen et al. 1986).
GIS analysis of road density
Through elimination of bounties and protection by the 1973 Endangered Species Act, wolves were provided protection that allowed recolonization of Wisconsin in the 1970s (Wydeven et al. 1995). Mladenoff et al. (1995) used a geographic information system (GIS) to assess landscape features that contributed to re-colonization of 14 Wisconsin wolf packs from 1980 to 1992. Known pack territories of radio-collared wolves were compared to 14 random non-pack areas scattered across northern Wisconsin. Areas occupied by wolf packs (80% isopleth of harmonic mean) had average road densities of 0.23 km/k[m.sup.2] (Table 1). Road density was based on paved roads, and improved dirt and gravel roads that appeared as solid lines on U.S. Geological Survey (USGS) 1:100,000 quadrangle maps (Mladenoff et al. 1995). …