Range expansion and ecological risk assessment for non-native wild pigs in California

Nonnative wild pigs (Sus scrofa) were established in California by 1850, and then expanded after the 1950s by domestic swine releases, hunting introductions and natural dispersal. The current distribution of wild pigs in California is closely associated with ecologically rich oak woodlands, where rooting is a major concern.  An extensive volume of research has identified specific problems caused by wild pigs. This study builds on prior work by integrating information on the current range and relative abundance of wild pigs for identifying native organisms at risk by exposure.  I used a large database of hunter harvest records, which, in combination with habitat modeling was applied to evaluating prospects for expansion.  Information on the current range of wild pigs was used in GIS analyses to identify native organisms in likely contact.  I processed a large database of digital maps of the estimated or actual distributions of 550 species of vertebrates and 1506 plants of conservation interest.  Risk of exposure was based on overlap between each species’ range at two levels; all wild pig range and high density wild pig range. The current range of wild pigs extends over 51,870 km² of California; the animal has spread into an additional 18,500 km² since 1996, and significant suitable but current non occupied habitat provides opportunities for continued expansion. Over 400 special status plants are exposed to wild pigs, including 72 that are rare, threatened or endangered.  Ranges of 324 vertebrates overlap with high density wild pigs, including 115 threatened or endangered organisms.  Fifty of these 115 vertebrates of conservation interest appear in close contact with pigs based on their life histories.