Interspecific Interactions among Wild Canids: Implications for the Conservation of Endangered San Joaquin Kit Foxes. (Canid Conservation)
Cypher, Brian L., Clark, Howard O., Jr., Kelly, Patrick A., Van Horn Job, Christine, Warrick, Gregory D., Williams, Daniel F., Endangered Species Update
Interspecific interactions among wild canids have significant implications for the conservation and recovery of endangered San Joaquin kit foxes (Vulpes macrotis mutica). Coyotes (Canis latrans) and non-native red foxes (V. vulpes) both engage in interference and exploitative competition with kit foxes. Several behavioral and ecological adaptations of kit foxes ameliorate such competition with coyotes and facilitate their coexistence. These adaptations include habitat partitioning, food partitioning, opportunistic foraging patterns, and year-round use of multiple dens. These adaptations are less effective against red foxes due to greater food and habitat overlap, the ability to pursue kit foxes into dens, and high potential for disease transmission. Thus, non-native red foxes pose a serious threat to kit foxes. Interactions between coyotes and red foxes may benefit kit foxes. In particular, interference competition by coyotes may limit the abundance and distribution of red foxes in the San Joaquin Valley. These interactions should be considered when evaluating management options (e.g., predator control).
Kit foxes are relatively small canids (1.7 to 3.0 kg) that occur in arid and semi-arid habitats of the southwestern United States and northern Mexico. The San Joaquin kit fox (Vulpes macrotis mutica) is a genetically distinct subspecies that historically occurred in the San Joaquin, Salinas, and Cuyama Valleys of central California. The abundance and range of this taxon have been significantly reduced, primarily due to habitat loss and degradation associated with agricultural, industrial, and urban development (FWS 1998). Fur harvests, predator control programs, and rodent control programs also may have contributed to observed declines. San Joaquin kit foxes persist as a metapopulation comprising three larger "core" populations and a number of smaller "satellite" populations. Current threats include continuing habitat conversion, rodenticide use, and interspecific competition. Much of the remaining habitat is fragmented, disturbed, and subject to competing land uses such as hydrocarbon production and water banking (FWS 1998). The San Joaquin kit fox was listed as Federally Endangered in 1967 and California Threatened in 1971.
Interspecific competition from other mammalian predators is an important factor affecting the remaining San Joaquin kit fox populations (Cypher et al. in press). Coyotes (Canis latrans), bobcats (Lynx rufus), gray foxes (Urocyon cineareoargenteus), badgers (Taxidea taxus), feral cats (Felis domesticus), and non-native red foxes (V. vulpes) all engage in interference and/or exploitative competition with kit foxes. Interference competition consists of direct mortality, harassment, and spatial exclusion. Exploitative competition consists of overlap in use of potentially limited resources such as food items and dens. Competitive interactions with coyotes and red foxes have the greatest implications for San Joaquin kit foxes. Our objectives for this paper are to summarize the competitive interactions that occur between kit foxes, coyotes, and red foxes, and to assess the potential implications of these interactions for kit fox conservation and recovery.
Coyotes engage in both interference and exploitative competition with kit foxes. Coyotes have long been recognized as a significant cause of mortality for kit foxes (Seton 1925). At various study sites throughout the range of the San Joaquin kit fox, coyotes are the primary source of kit fox mortality for which the cause of death is identifiable (Hall 1983; Briden et al. 1992; Standley et al. 1992; Ralls and White 1995; Spiegel and Disney 1996; Cypher et al. 2000). This mortality indeed appears to be the result of competition rather than predation. Coyotes commonly do not consume the kit foxes they kill (Spiegel and Disney 1996; Cypher and Spencer 1998), although over half of kit foxes killed at one location were consumed during a period of low food availability (Ralls and White 1995). …