Intraguild Competition between Endangered Kit Foxes and a Novel Predator in a Novel Environment

SIMPLE SUMMARY: A population of endangered San Joaquin kit foxes inhabits the urban environment in the city of Bakersfield, California, United States. Non-native red foxes, a larger competitor, also occur in Bakersfield and are a potential threat to kit foxes. Based on scat analysis, dietary overlap between the two species is high and red foxes have usurped kit fox dens. Based on logistic regression, habitat attributes generally were similar between grid cells used by each species. However, kit foxes tended to use areas with smaller open spaces and more human activity. We also found that the two species almost never overlapped temporally when using the same grid cells. Because of this temporal separation in addition to an abundance of food and dens in the urban environment, competition from red foxes does not currently appear to be a significant threat to kit foxes. ABSTRACT: A population of endangered San Joaquin kit foxes inhabits the urban environment in the city of Bakersfield, California, United States. This population is considered important for the conservation and recovery of this species. In this novel environment, kit foxes encounter a novel competitor, that being non-native red foxes. We examined exploitative and interference competition between these two species. Based on scat analysis, both species consumed similar foods and dietary overlap was high. Red foxes also were found to usurp kit fox dens. Direct mortality to kit foxes from red foxes appears to be rare. Kit foxes and red foxes also appear to overlap spatially, although we found evidence of temporal partitioning of shared space. Based on binary logistic regression modeling, habitat attributes in grid cells used by the two species generally were similar, consistent with the spatial overlap. However, differences in specific attributes indicated that kit foxes are more likely to use areas with smaller open spaces and more human activity compared to red foxes. Competition from red foxes may be mitigated by several factors. Critical resources such as food and dens may be sufficiently abundant such that they are not a limiting factor. Some degree of spatial segregation and temporal partitioning of shared space may reduce interference competition. These factors may facilitate coexistence, and consequently, red foxes do not currently appear to constitute a significant competitive risk to this important population of endangered San Joaquin kit foxes.