Context. The San Joaquin kit fox (Vulpes macrotis mutica) is listed as endangered in the United States and threatened in California. Primary processes influencing populations of this mesocarnivore are not well quantified. Aims. The study aim was to determine whether bottom up or top down processes most influenced the demography and ecology of kit foxes. Methods. During 2014-19, we assessed prey abundance on 60 0.5-km transects, food item use by kit foxes and coyotes (Canis latrans) by examining scats, abundance of both canids using camera stations, and kit fox survival, reproduction, and space use during low and high prey periods using radio-telemetry. Coyotes are the main kit fox predator. Key results. Due to higher precipitation, prey abundance increased markedly during the study period. Dietary overlap between kit foxes and coyotes was high in all years (0.73-0.92). Abundance of both kit foxes and coyotes increased as did overlap at camera stations. Between low and high prey years, survival (0.69 vs 0.87) and reproductive success (44.4% vs 72.7%) of kit foxes trended higher and mean home range size decreased significantly (4.3 km2 vs 1.3 km2). Conclusions. As prey increased, kit fox abundance, survival, and reproduction all responded positively despite a concomitant increase in the abundance of their main competitor, coyotes, and a high potential for interference and exploitative competition. We concluded that bottom up processes are more influential on kit foxes than top down processes. Management strategies that enhance prey abundance, such as grazing in wet years, should benefit kit foxes.
Cypher et al. (Thu,) studied this question.