Cultural and regulatory factors influence distribution and trajectory of invasive species in the United States: A wild pig case study.

Since 2012, control of invasive wild pigs (Sus scrofa) in the United States (US) has become a state and national priority due to their propensity to damage agricultural commodities and infrastructure, transmit disease, detrimentally affect ecological processes, and compete with native wildlife for resources. While several life-history characteristics certainly aided their proliferation, the recreational value of wild pigs was likely the stimulus for translocation and subsequent establishment of populations in ≥35 states, causing an annual economic burden of $1.5 billion in the US. Consequently, state-level legislative procedures regarding wild pigs are expanding in scope and priority, but policy among states lacks uniformity. States vary in their treatment of wild pig control based on differing resource appropriations and stakeholder interests. We conducted an evaluation to determine if policy was associated with state-level 1) presence of wild pigs, 2) spatial extent of wild pig population occupancy, and 3) trajectory of wild pig population occupancy. Our results suggest the presence of wild pigs in various states was influenced by hunting preserves and the sale of hunting opportunities. In occupied states, the spatial extent of wild pigs was again associated with the sale of hunting opportunities and a wild pig hunting culture. Finally, the trajectory of state-level wild pig spatial occupancy was positively influenced by the sale of hunting opportunities, and negatively influenced by transportation policies. Based on these findings, we propose state governments standardize transportation policy and fenced hunting regulations across regions of the US in a more prohibitive fashion to diminish range expansion through illegal and negligent introductions via transportation, release, and escapes from game farms. Moreover, in states where wild pigs have yet to establish, we strongly recommend states proactively prohibit transportation through intra- and interstate movement.