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Spread of wild pigs in the contiguous United States. This map illustrates cumulative documented occurrence of wild pigs from 1982 to 2012 based on Southeastern Cooperative Wildlife Disease Study (SCWDS) records aggregated to watersheds (Hydrologic Unit Code 10). Areas occupied by wild pigs in a given year continue to be occupied in later years, with rare exception.
Source publication
Wild pigs (Sus scrofa), also known as wild swine, feral pigs, or feral hogs, are one of the most widespread and successful invasive species around the world. Wild pigs have been linked to extensive and costly agricultural damage and present a serious threat to plant and animal communities due to their rooting behavior and omnivorous diet. We modele...
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Citations
... In the US, wild pigs are one of the most economically costly (Pimentel 2007;Anderson et al. 2016;Holderieath 2016;Anderson et al. 2019;McKee et al. 2020, Fantle-Lepczyk et al. 2022) and ecologically destructive (Siemann et al. 2009;Jolley et al. 2010;Barrios-Garcia and Ballari 2012;Bevins et al. 2014) invasive species. Much of the wild pig population in the continental US is concentrated in the Southeast (McClure et al. 2015), particularly on privately owned land. As a result, private landowners directly experience many of the negative environmental, economic, human health, and wildlife impacts associated with wild pigs. ...
Successful management of invasive species often requires working across public and private landownerships. A prime example of an invasive species that commonly occurs on privately and publicly owned and managed lands is the wild pig (Sus scrofa). Because of the multitude of negative impacts associated with wild pigs, management must occur across both private and public lands to achieve widespread control and sustained success. However, managing wild pigs across property boundaries is challenging as we know very little about differing management practices and landowner perspectives. To address this knowledge gap, we sought to understand wild pig management efforts on privately owned lands, the perceived economic, ecological, and human health impact of wild pigs, and beliefs related to policy. Generally, stakeholders believe wild pigs have negative impacts on wildlife, the economy, and ecological and public health, however less than half of landowners participate in wild pig control. Furthermore, stakeholders believe that the responsibility of managing and paying for damages associated with wild pigs lies with individual landowners. Our findings suggest that increased efficacy of wild pig control and collaboration between private and public landowners is not only possible but also necessary if wild pig population control is to be regionally successful.
... Although invasive wild pigs represent a global challenge, this species is of particular concern in the United States where abundance and distribution have expanded exponentially since the 1980s (McClure et al., 2015;Nolte & Anderson, 2015;Snow et al., 2017). In the absence of a native wild suid, any free-ranging swine encountered in the United States would be considered an invasive wild pig regardless of domestic origin (derived from livestock production systems or the pet trade [i.e., Vietnamese potbellied pigs]), wild origin (Eurasian wild boar), or hybrids of these lineages. ...
The rapid expansion of wild pigs (Sus scrofa) throughout the United States has been fueled by unlawful introductions, with invasive populations causing extensive crop losses, damaging native ecosystems, and serving as a reservoir for disease. Multiple states have passed laws prohibiting the possession or transport of wild pigs. However, genetic and phenotypic similarities between domestic pigs and invasive wild pigs-which overwhelmingly represent domestic pig and wild boar hybrids-pose a challenge for the enforcement of such regulations. We sought to exploit wild boar ancestry as a common attribute among the vast majority of invasive wild pigs as a means of genetically differentiating wild pigs from breeds of domestic pig found within the United States. We organized reference high-density single nucleotide polymor-phism genotypes (1039 samples from 33 domestic breeds and 382 samples from 16 wild boar populations) into five genetically cohesive reference groups: mixed-commercial breeds, Durocs, heritage breeds, primitive breeds, and wild boar. Building upon well-established genetic clustering approaches, we structured the test statistic to describe the difference in the likelihood of a given genotype's ancestry vectors (sensu genetic clustering analysis) if derived strictly from the four described domestic pig reference groups versus allowing for admixture from the wild boar group. By fitting statistical distributions to test statistics of reference domestic pigs, we characterized the distribution of the null hypothesis that a given genotype descends strictly from domestic pig reference groups. We tested the approach with simulated genotypes and empirical data from an additional 29 breeds of domestic pig represented by 435 unique genotypes; all associated test statistics for simulated and empirical domestic pig challenge sets fell within the distribution of reference domestic pigs. We then evaluated 6566 invasive wild pigs sampled across the contiguous United States, of which 63% exceeded the maximum threshold for domestic pigs and could be statistically classified as possessing wild boar ancestry. This approach provides a scientific foundation to enforce regulations prohibiting the possession of this destructive invasive species. Further, this computationally efficient and generalizable approach could be readily adapted to quantify gene flow among ecological systems of conservation or management concern.
... In parts of Asia where they have been studied, feral swine appear to play an important role in JEV transmission and are not subject to preventative immunization [52]. Feral swine populations are expanding in the US, and their distribution is principally in warm climates of the Gulf Coast, from Florida to Texas [53]. This fact favors mosquito-borne transmission. ...
Japanese encephalitis virus is a mosquito-borne member of the Flaviviridae family. JEV is the leading cause of viral encephalitis in Asia and is characterized by encephalitis, high lethality, and neurological sequelae in survivors. The virus also causes severe disease in swine, which are an amplifying host in the transmission cycle, and in horses. US agricultural authorities have recently recognized the threat to the swine industry and initiated preparedness activities. Other mosquito-borne viruses exotic to the Western Hemisphere have been introduced and established in recent years, including West Nile, Zika, and chikungunya viruses, and JEV has recently invaded continental Australia for the first time. These events amply illustrate the potential threat of JEV to US health security. Susceptible indigenous mosquito vectors, birds, feral and domestic pigs, and possibly bats, constitute the receptive ecological ingredients for the spread of JEV in the US. Fortunately, unlike the other virus invaders mentioned above, an inactivated whole virus JE vaccine (IXIARO®) has been approved by the US Food and Drug Administration for human use in advance of a public health emergency, but there is no veterinary vaccine. This paper describes the risks and potential consequences of the introduction of JEV into the US, the need to integrate planning for such an event in public health policy, and the requirement for additional countermeasures, including antiviral drugs and an improved single dose vaccine that elicits durable immunity in both humans and livestock.
... In parts of Asia where they have been studied, feral swine appear to play an important role in JEV transmission and are not subject to preventative immunization [50]. Feral swine populations are expanding in the US, and their distribution is principally in warm climates of the states Gulf Coast from Florida to Texas [51], favoring mosquito-borne transmission. The proximity of feral pigs to airports that might be the points of introduction of infected adult mosquitoes is uncertain, but it is worthy of mention that at least one major international airport in Europe serving Asia has intentionally placed pigs in surrounding fields to prevent bird strikes [52]. ...
Japanese encephalitis virus is a mosquito-borne member of the Flaviviridae family. JEV is the leading cause of viral encephalitis in Asia and is characterized by encephalitis, high lethality and neurological sequelae in survivors. The virus also causes severe disease in swine, which are an amplifying host in the transmission cycle, and in horses. US agricultural authorities have recently recognized the threat to the swine industry and initiated preparedness activities. Other mosquito-borne viruses exotic to the Western Hemisphere have been introduced and established in in recent years, including West Nile, Zika, and chikungunya viruses, and JEV has recently invaded continental Australia for the first time. These events amply illustrate the potential threat of JEV to US health security. Susceptible indigenous mosquito vectors, birds, feral and domestic pigs, and possibly bats, constitute the receptive ecological ingredients for spread of JEV in the US. Fortunately, unlike the other virus invaders mentioned above, an inactivated whole virus JE vaccine (IXIARO®) has been approved by the US Food & Drug Administration for human use in advance of a public health emergency, but there is no veterinary vaccine. This paper describes the risks and potential consequences of introduction of JEV in the US, the need to integrate planning for such an event in public health policy and the requirement for additional countermeasures, including antiviral drugs and an improved single dose vaccine that elicits durable immunity in both humans and livestock.
... Historically, feral swine populations were composed of domestic pigs that were either released or escaped as a consequence of free-range livestock practices; however, contemporary populations generally represent animals of mixed wild boar and domestic pig ancestry following the importation of European wild boar for hunting purposes (Smyser et al., 2020). Despite their long history in the US, the distribution of feral swine has expanded dramatically in recent years largely due to humanfacilitated movement (i.e., translocation; Bevins et al., 2014;McClure et al., 2015;Snow et al., 2017;Tabak et al., 2017;Hernández et al., 2018a;Smyser et al., 2020). This expansion increases the risk of disease spillover, as feral swine are now established in agricultural productions regions with domestic livestock, poultry, and cervids that demonstrate susceptibility to feral swine pathogens . ...
Pseudorabies virus (PRV)—the causative agent of Aujeszky’s disease—was eliminated from commercial pig production herds in the United States (US) in 2004; however, PRV remains endemic among invasive feral swine (Sus scrofa). The circulation of PRV among abundant, widespread feral swine populations poses a sustained risk for disease spillover to production herds. Risk–based surveillance has been successfully implemented for PRV in feral swine populations in the US. However, understanding the role of host genetics in infection status may offer new insights into the epidemiology and disease dynamics of PRV that can be applied to management strategies. Genetic mechanisms underlying host susceptibility to PRV are relatively unknown; therefore, we sought to identify genomic regions associated with PRV infection status among naturally infected feral swine using genome–wide association studies (GWAS) and gene set enrichment analysis of single nucleotide polymorphism data (GSEA–SNP). Paired serological and genotypic data were collected from 6,081 feral swine distributed across the invaded range within the contiguous US. Three complementary study populations were developed for GWAS: 1) comprehensive population consisting of feral swine throughout the invaded range within the contiguous US; 2) population of feral swine under high, but temporally variable PRV infection pressure; and 3) population of feral swine under temporally stable, high PRV infection pressure. We identified one intronic SNP associated with PRV infection status within candidate gene AKAP6 on autosome 7. Various gene sets linked to metabolic pathways were enriched in the GSEA–SNP. Ultimately, improving disease surveillance efforts in feral swine will be critical to further understanding of the role host genetics play in PRV infection status, helping secure the health of commercial pork production.
... [10][11][12][13] 13 Expansion of agricultural lands, in particular, can facilitate the expansion of wild pig populations through providing both cover and high-quality forage. 10,[14][15][16] Wild pigs are omnivorous, 17 have high reproductive rates, and low mortality due to predation, even when young, 18,19 which has hastened wild pig range expansion into new regions and habitats. 20 In natural ecosystems, wild pigs can severely damage native habitats and sensitive ecological communities, especially riparian areas and deciduous forests. ...
BACKGROUND
As the population and range of wild pigs (Sus scrofa) continue to grow across North America, there has been an increase in environmental and economic damages caused by this invasive species, and control efforts to reduce damages have increased concomitantly. Despite the expanding impacts and costs associated with population control of wild pigs, the extent to which wild pig control reduces populations and diminishes environmental and agricultural damages are rarely quantified. The goal of this study is to quantify changes in wild pig relative abundance and subsequent changes in damages caused by invasive wild pigs in response to control.
RESULTS
Using a combination of wild pig population surveys, agricultural damage assessments, and environmental rooting surveys across 19 mixed forest‐agricultural properties in South Carolina, USA, we quantified changes in wild pig relative abundance and associated damages over a 3‐year period following implementation of a professional control program. Following implementation of control efforts, both the number of wild pig detections and estimated abundance decreased markedly. Within 24 months relative abundance was reduced by an average of ~70%, which resulted in a corresponding decline in environmental rooting damage by ~99%.
CONCLUSION
Our findings suggest that sustained wild pig control efforts can substantially reduce wild pig relative abundance, which in turn resulted in a reduction in environmental rooting damage by wild pigs. Ultimately this study will help fill critical knowledge gaps regarding the efficacy of wild pig control programs and the effort needed to reduce impacts to native ecosystems, livestock, and crops. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
... However, wild pigs have limited thermoregulatory capabilities and often are associated with areas proximal to water and associated vegetation types 33,34 . Previous research has shown wild pigs have smaller home ranges, a higher likelihood of occurrence, and a higher likelihood of invasion in areas near water 21,[35][36][37] . These areas frequently have concentrated resources important to wild pigs including overstory cover, access to water, and a diversity of forage resources [38][39][40][41][42] . ...
... to define landcover types. To consolidate NLCD landcover categories to those most relevant to wild pig movements 34,36,37 and probability of occurrence 35 , we reclassified the NLCD GIS layer into seven land cover types (bottomland hardwood, deciduous upland forest, conifer forest, shrub/herbaceous, open water, cropland, and developed). We considered herbaceous and woody wetlands categories within the NLCD as representing bottomland hardwoods and shrub/scrub and herbaceous categories were aggregated as a shrub/herbaceous. ...
Background
Data on the movement behavior of translocated wild pigs is needed to develop appropriate response strategies for containing and eliminating new source populations following translocation events. We conducted experimental trials to compare the home range establishment and space‐use metrics, including the number of days and distance traveled before becoming range residents, for wild pigs translocated with their social group and individually.
Results
We found wild pigs translocated with their social group made less extensive movements away from the release location and established a stable home range ~5 days faster than those translocated individually. We also examined how habitat quality impacted the home range sizes of translocated wild pigs and found wild pigs maintained larger ranges in areas with higher proportion of low‐quality habitat.
Conclusion
Collectively, our findings suggest translocations of invasive wild pigs have a greater probability of establishing a viable population near the release site when habitat quality is high and when released with members of their social unit compared to individuals moved independent of their social group or to low‐quality habitat. However, all wild pigs translocated in our study made extensive movements from their release location, highlighting the potential for single translocation events of either individuals or groups to have far‐reaching consequences within a much broader landscape beyond the location where they are released. These results highlight the challenges associated with containing populations in areas where illegal introduction of wild pigs occurs, and the need for rapid response once releases are identified. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
... Found in all Brazilian biomes, wild boars have been already reported in Colombia, Argentina, Uruguay and Chile, expectedly invading ecoregions overlaying Bolivia and Paraguay [69]. As invasive wild pigs across the contiguous USA from 1982 to 2012 were driven by higher habitat heterogeneity and limited only by cold temperatures and water scarcity [70], widespread may be faster in South American biomes, which provide access to multiple key resources including biodiversity, water, forage, and shelter. ...
... Population monitoring has been another important wild boar issue. Ideally, digital cartography of vegetation coverage to map habitat suitability for wild boars should be made, in association with the georeferenced and presence records, to predict and analyze population dynamics, as proposed for Bulgaria, and reported by Poland, Germany, Switzerland, Italy, Portugal and Spain in Europe [101], and in the USA [70]. Although wild pigs have invaded all biomes and almost all Brazilian regions, with high densities in the tropical forests of the Atlantic Forest, few studies have mapped [102]. ...
Wild boars have been listed among the 100 most invasive species worldwide, spreading impacts to all continents, with the exception of Antarctica. In Brazil, a major source of introduction was a commercial livestock importation for exotic meat market, followed by successive escapes and releases to natural ecosystems. Currently found in all six Brazilian biomes, with reports in 11 Brazilian states, wild boars have invaded natural and agricultural areas. Wild boars have been reportedly indicated as hosts and reservoirs of several zoonotic diseases in Brazil, including toxoplasmosis, salmonelosis, leptospirosis, brucellosis, tuberculosis, trichinellosis, and hepatitis E. Wild boars have been also associated with Brazilian spotted fever and rabies, infected while providing plentiful exotic blood supply for native ticks and hematophagous bats. Due to their phylogenetic proximity, wild boars may present ecological niche overlapping and direct disease risk to native white-lipped and collared peccaries. Moreover, wild boars may post an economical threat to Brazilian livestock industry due to restrictive diseases such as Aujeszky, enzootic pneumonia, neosporosis, hemoplasmosis, and classic swine fever. Finally, wild boars have directly impacted in environmentally protected areas, silting up water springs, rooting and wallowing native plants, decreasing native vegetal coverage, disbalancing of soil components, altering soil structure and composition. Wild boar hunting has failed as a control measure to date, according to the Brazilian Ministry of Environment, due to private hunting groups mostly targeting males, intentionally leaving females and piglets alive, disseminating wild boar populations nationwide. Meanwhile, non-government animal welfare organizations have pointed to animal cruelty of hunting dogs and wild boars (and native species) during hunting. Despite unanimous necessity of wild boar control, eradication and prevention, methods have been controversial and should focus on effective governmental measures instead occasional game hunting, which has negatively impacted native wildlife species while wild boars have continuously spread throughout Brazil.
... Nevertheless, their reproductive biology retains this variability of fecundity, which can cause populations to rapidly grow and establish following introduction in new environments, leading to the further expansion of this species. Despite significant efforts to forecast the spread of wild pigs (Snow et al. 2017), estimate the probability of occurrence (McClure et al. 2015), and predict the potential density of wild pig populations (Lewis et al. 2017) there are no available spatial predictions of population growth and establishment risk if wild pigs were released into a given spatial location. ...
... These data describing the known distribution of wild pigs were compiled at irregular intervals from 1982 to 2008 and annually since 2008. They are the best available data describing the known distribution of wild pigs over the past 36 years and have been used to forecast the spread of wild pigs (Snow et al. 2017), estimate the probability of occurrence (McClure et al. 2015), determine wild pig agricultural damage risk , predict federal policy to control wild pigs , and determine the risk wild pigs pose to imperiled species (McClure et al. 2018). Polygons representing the known geographic extent of established wild pig populations (defined as populations present for two or more years with evidence of reproduction) are reported to the National Feral Swine Mapping System nationally by wildlife professionals in state wildlife resource agencies and the United States Department of Agriculture. ...
... Polygons representing the observed distribution for 1982, 1988, 2004, 2008, 2013, 2017, and 2021 were aggregated to watershed boundary data as described in McClure et al. (2015) to discretize consistent, comparable, and ecologically relevant sampling units. We selected the sub-watershed unit (hydrologic unit code 12; HUC12) as our primary sampling unit for several reasons. ...
Invasion of nonindigenous species is considered one of the most urgent problems affecting native ecosystems and agricultural systems. Mechanistic models that account for short-term population dynamics can improve prediction because they incorporate differing demographic processes that link the environmental conditions of a spatial location explicitly with the invasion process. Yet short-term population dynamics are rarely accounted for in spatial models of invasive species spread.
Accounting for transient (short-term) population dynamics that arise from the interaction of age structure and vital rates, we predict the stochastic population growth rate and establishment probability of wild pigs following introduction into any location in North America. Established ecological theory suggests that the rate of spatial spread is proportional to population growth rate. Using observed geographic distribution data for wild pigs we calculated geographic spread rates (watersheds/year) from 1982 to 2021. We investigated if observed spread rates increased in watersheds with higher stochastic population growth rates. Stochastic population growth rate and establishment probability of wild pigs increased with increasing initial population (propagule) size and length of establishment time. Areas along the Mississippi, Ohio, and lower portions of the Missouri river drainages had the highest probability of wild pig establishment with many regions having probabilities close to 1. Spread rates demonstrated strong spatial heterogeneity with the greatest rates of spread (5.8 watersheds/year) occurring from 2008 to 2013 prior to the establishment of a National wild pig control program in 2013. Spread rates declined 82% (0.57 watersheds/year) in the period from 2013 to 2021 compared to the period from 1982 to 2013. We found significant positive associations among stochastic population growth rate and observed geographic rates of spread. Stochastic population growth rate explained a large amount of variation (79.3–92.1%) in annual rate of watershed spread of wild pigs. Our predicted probabilities of establishment and population growth can be used to inform surveillance and control efforts to reduce the potential for establishment and spread of wild pigs.
... southern North America as early as the sixteenth century by Spanish explorers (McClure et al. 2015). These animals are a nonindigenous, invasive species in the U.S. and are typically referred to as feral swine, feral hogs, or wild hogs. ...
We trapped, anesthetized, and fit 16 female feral swine (Sus scrofa) with Global Positioning System (GPS) collars in Great Smoky Mountains National Park (GRSM) to develop predictive summer and winter models for more effective population control efforts. Given the highly diverse habitat and topography in GRSM and the spatial extent of our dataset, we employed Step Selection Function (SSF) to evaluate resource selection at the 3rd-order level and Resource Selection Function (RSF) models at the 2nd-order level for both summer and winter seasons. The summer SSF and RSF models suggested relatively similar levels of selection, whereas the winter models differed by method. We created a straightforward consensus model to better visualize the agreement and constraints of each set of models. In summer, feral swine used lower slopes regardless of elevation, especially those closer to human-dominated spaces such as along paved and gravel roadways. In winter, feral swine maintained preference for lower slopes but preferred oak-dominated forest areas and selection for human development was less than in summer. Wildlife managers can use these models to better focus feral swine surveillance and management in GRSM. Managers can identify areas of high use by season and plan control activities that are both accessible and highly efficient. The combination and consensus framework presented here can be applied to other systems where species’ habitat selection may result in incongruous results across different levels of selection or seasons of interest.
