Effects of varying habitats on competition between endangered San Joaquin kit foxes (Vulpes macrotis mutica) and Coyotes (Canis latrans)

Abstract

Coyotes (Canis latrans) are the primary predator of endangered San Joaquin kit foxes (Vulpes macrotis mutica). Coyotes often associate with coverrich habitats while kit foxes use grasslands, alkali shrublands, and urban environments. Effects of varying habitats on coyote and kit fox competition are relatively unknown. I assessed exploitation and interference competition between coyotes and kit foxes in grassland and shrubland habitats to determine if kit foxes are niche displaced by coyotes. I evaluated habitat and spatial partitioning, diet, and prey abundance of kit foxes and coyotes, as well as survival and fecal glucocorticoid levels (GC) of kit foxes at the Lokern Natural Area in central California from January 2003 through June 2004. Kit foxes partitioned habitat, space, and diet with coyotes. Coyotes primarily used shrubland habitats while kit foxes selected for burned grasslands that coyotes avoided. Kit foxes and coyotes had high dietary overlap, though coyotes had higher dietary breadth than kit foxes, creating significant differences in their diets. Kit fox scats recovered in grasslands showed preference for the larger kangaroo rat, Dipodomys heermanni, which was closely tied to shrub habitats. Predation was the primary source of mortality for kit foxes and was greater in the shrublands than grasslands. As a result of increased predation in shrublands, kit foxes with home ranges containing greater proportions of shrub had lower survival rates than foxes residing in grasslands. Despite increased predation risk in shrublands, I detected no difference in kit fox GC levels in shrubland versus grassland habitats, indicating that use of shrub habitats did not produce a physiological stress response in kit foxes. Results suggest that a heterogeneous landscape may allow for the parsimonious coexistence of San Joaquin kit foxes and coyotes. I also analyzed fecal glucocorticoid levels of kit foxes in rural and urban environments to assess the effect of various environments on kit fox stress responses. I detected no difference in glucocorticoid levels in kit foxes residing in urban compared to rural environments, suggesting that the niche shift from traditional rural habitats to the urban setting does not carry physiological costs due to chronic stress responses.