Interpreting and predicting the spread of invasive wild pigs

Abstract

Summary1. The eruption of invasive wild pigs (IWPs) Sus scrofa throughout the world exemplifies the need to understand the influences of exotic and nonnative species expansions. In particular, the continental USA is precariously threatened by a rapid expansion of IWPs, and a better understanding of the rate and process of spread can inform strategies that will limit the expansion. 2. We developed a spatially and temporally dynamic model to examine three decades of IWP expansion, and predict the spread of IWPs throughout the continental USA, relative to where IWPs previously inhabited. We used the model to predict where IWPs are likely to invade next. 3. The average rate of northward expansion increased from 6Á5 to 12Á6 km per year, suggesting most counties in the continental USA could be inhabited within the next 3-5 decades. The spread of IWPs was primarily associated with expansion into areas with similar environmental characteristics as their previous range, with the exception of spreading into colder regions. We identified that climate change may assist spread into northern regions by generating milder winters with less snow. Otherwise, the spread of IWPs was not dependent on agriculture, precipitation or biodiversity at the county level. The model correctly predicted 86% of counties that were invaded during 2012, and those predictions indicate that large portions of the USA are in immediate danger of invasion. 4. Synthesis and applications. Anti-invasion efforts should focus along the boundaries of current occupied range to stop natural expansion, and anti-invasion policies should focus on stopping anthropogenic transport and release of invasive wild pigs. Our results demonstrate the utility of a spatio-temporal examination to inform strategies for limiting the spread of invasive wild pigs.

Mixed ancestry from wild and domestic lineages contributes to the rapid expansion of invasive feral swine

“…Accordingly, the proliferation of European wild boar ancestry among invasive feral swine populations despite limited initial introductions could be attributable to fitness advantages conveyed by unique behavioural or morphological characteristics of domestic pig–wild boar hybrids. Furthermore, increases in wild boar ancestry among newly emergent feral swine populations could result from the intensification of environmental selective pressures if the fitness advantages of individuals with wild boar phenotypic attributes become greater as limiting factors, such as winter severity, become more restrictive with northward and inland range expansion (McClure et al, 2015; Snow et al, 2017). Support for the assertion that domestic pig–wild boar hybrids may be highly invasive can be drawn from the observed introgression of domestic pigs into native European wild boar populations and subsequent proliferation of admixed genotypes among wild populations in Europe (Fulgione et al, 2016; Goedbloed, Hooft, et al, 2013; Goedbloed, Megens, et al, 2013).…”

“…Specifically, we differentiated samples as being from either long‐established populations—those counties invaded by feral swine as of 1988 or earlier—or newly emergent populations—those counties invaded by feral swine between 1988 and 2017, when our most recent samples were collected (Figure 1; National Feral Swine Mapping System; Southeastern Cooperative Wildlife Disease Study, 2015). The distribution of counties invaded by feral swine in 1988 was selected for comparison as: (a) this represented the finest spatial distribution for which historical feral swine distributions were available, (b) earlier mapping efforts (i.e., 1982; Southeastern Cooperative Wildlife Disease Study, 2015) probably suffered from reporting bias due to a lack of awareness of feral swine as a natural resources management concern, and (c) 1988 represents a temporal demarcation from the slow spatial expansion of historical feral swine populations to the rapid acceleration of invasion observed recently (Bevins et al, 2014; McClure et al, 2015; Nolte & Anderson, 2015; Snow et al, 2017). Treating individual invasive feral swine ancestry vectors as a compositional response variable, we used the r package compositions (van den Boogaart, Tolosana‐Delgado, & Bren, 2019) to test for general differences in ancestry across all reference clusters between long‐established and newly emergent populations.…”

A preliminary investigation of wild pig (Sus scrofa) impacts in water quality

“…Wild pigs ( Sus scrofa ) are a pervasive and highly destructive pest, affecting economic, environmental, and human health values around the world (Bengsen, Gentle, Mitchell, Pearson, & Saunders, ; Snow, Jarzyna, & VerCauteren, ; Valéry, Fritz, Lefeuvre, & Simberloff, ). The impacts of wild pigs has been recognized under governmental legislation (e.g., Australia) as threatening many native species and communities through direct predation, habitat degradation, competition, and disease transmission (Bengsen et al., ).…”

Attractants for wild pigs: current use, availability, needs, and future potential

“…As the range of wild pigs expands, along with development of Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10344-017-1144-z) contains supplementary material, which is available to authorized users. lands for human uses, human-wild pig conflicts will escalate, emphasizing the need for improved management options (Saito et al 2012;Snow et al 2016a).…”

“…Wild pigs have been introduced into numerous countries with substantial populations in the USA and Australia (AU) (Spencer and Hampton 2005;Snow et al 2016a). Populations continue to expand due to their adaptability and high reproductive potential as well as intentional translocations and releases (Bevins et al 2014).…”