Invasive mammalian carnivores contribute disproportionately to declines in global biodiversity. In California, nonnative red foxes (Vulpes vulpes) have significantly impacted endangered ground-nesting birds and native canids. These foxes derive primarily from captive-reared animals associated with the fur-farming industry. Over the past five decades, the cumulative area occupied by nonnative red fox increased to cover much of central and southern California. We used a landscape-genetic approach involving mitochondrial DNA (mtDNA) sequences and 13 microsatellites of 402 nonnative red foxes removed in predator control programs to investigate source populations, contemporary connectivity, and metapopulation dynamics. Both markers indicated high population structuring consistent with origins from multiple introductions and low subsequent gene flow. Landscape-genetic modeling indicated that population connectivity was especially low among coastal sampling sites surrounded by mountainous wildlands but somewhat higher through topographically flat, urban and agricultural landscapes. The genetic composition of populations tended to be stable for multiple generations, indicating a degree of demographic resilience to predator removal programs. However, in two sites where intensive predator control reduced fox abundance, we observed increases in immigration, suggesting potential for recolonization to counter eradication attempts. These findings, along with continued genetic monitoring, can help guide localized management of foxes by identifying points of introductions and routes of spread and evaluating the relative importance of reproduction and immigration in maintaining populations. More generally, the study illustrates the utility of a landscape-genetic approach for understanding invasion dynamics and metapopulation structure of one of the world's most destructive invasive mammals, the red fox.

Introduced red fox in urban Orange County, California ate a wide variety of foods. Mammals and birds were consumed at all times of the year and both taxa appeared in approximately half or more of the fecal samples at all times of the year. Human supplied food remains were also common and supplemental feeding occurred at all study sites. Supplemental feeding has the potential to exacerbate problems for management of introduced red fox and several endangered species.

Since the late 1800s, non-native red foxes have been introduced in California for fur farming and fox hunting. Dispersal, population growth, and extensive translocations by humans have aided the expansion of the nonnative fox population throughout many of the lowland and coastal areas of the state. Since the 1980s, non-native red foxes have been recognized as predators of a number of endangered species. Trapping and euthanizing non-native red foxes have been used as methods to protect these endangered species, but have been opposed by some members of the public. Opposition by animal rights groups to red fox trapping and euthanization has significantly influenced the management actions and policies of wildlife agencies. Red foxes are among the wildlife species commonly recognized in our culture; however, their historical use as a commodity and a game animal, and their impact on several endangered species, make them a difficult and controversial species to manage. Both fox biology and the public place great demands on wildlife agencies to develop new, proactive management strategies for non-native red foxes.