Co‐occurrence of native white‐tailed deer and invasive wild pigs: Evidence for competition?

Abstract

Understanding whether invasive and native species compete for shared resources where they co-occur is essential for mitigating the negative impacts of invasive species on native ecosystems. Here, we examined how the presence and density of an invasive species, wild pigs (Sus scrofa), affect native white-tailed deer (Odocoileus virginianus; hereafter, deer) on the Savannah River Site, SC, USA. We examined potential changes in deer areas of use, temporal overlap, and occupancy to evaluate the effects of wild pig occurrence and density on deer space use, diel activity, and co-occurrence with wild pigs across 9 months during 2018 and 2019. Wild pig density had the strongest effect on deer space use in high-and moderate-use areas. Declines in deer space use in response to wild pig density were most pronounced in March and October 2018 and April 2019 for females, while male space use declined in response to wild pig density in October and December 2018. Both species were largely nocturnal with high overlap in diel activity across months. Deer occupancy responses to wild pig density varied across months, with negative responses in May and October 2018 and positive responses in July 2018 and April 2019. Deer and wild pigs co-occurred at 30%-59% of camera stations across months, with broadscale co-occurrence patterns being unaffected by changes in shared cover or wild pig occurrence. Overall, our results suggest that deer make fine-scale behavioral adjustments to avoid wild pigs, providing evidence that competition is likely occurring even where wild pig density is relatively low. Such fine-scale behavioral plasticity in deer appears to mitigate the costs of competition with wild pigs and may be a mechanism enabling long-term co-existence of deer and wild pigs. Our study provides novel insight on the complexities of spatiotemporal relationships between invasive wild pigs and native deer and suggests that the negative effects of interactions between deer and wild pigs may be more pronounced when deer life history needs are particularly demanding. In areas where eradication of invasive wild pigs may be impossible, maintaining low wild pig densities may help mitigate, but may not eliminate, the negative effects of wild pigs on deer.

Spatiotemporal overlap with invasive wild pigs (Sus scrofa) varies by species and season in a temperate ecosystem

“…Wild pigs were recorded in McCormick County before 2005 and continue to spread to new areas, despite 10 years of population control in the county. Abundance is nonetheless lower in McCormick County than nearby counties and, based on wildlife camera surveys, density appears lower in our study area relative to other areas in South Carolina along the nearby Savannah River (Garabedian et al, 2023). Opportunistically shot on sight or captured in box traps, approximately 135 wild pigs were removed from our study area over three years.…”

“…It is also plausible that the relatively low density of wild pigs in our study area compared with nearby areas, rather than shortcomings in our analytical techniques, obscured potential negative or positive impacts on species that could emerge if wild pig density were to increase. For instance, at the Savannah River Site in South Carolina, wild pig effects on deer space use increased with increasing wild pig density (Garabedian et al, 2023). It is also possible our results were influenced by wild pig harvest and removal efforts, as 40 were removed across the study area in 2019 and there was low detection in the first half of 2020, despite only a sow and boar being removed during that time.…”

“…The potential for interspecific competition due to niche overlap can change across spatiotemporal scales based on the resource selection of the species involved (Crombie, 1947). Animals can be displaced by both direct and indirect competition with wild pigs (Barrios‐García & Ballari, 2012; McDonough et al, 2022), or may actively reduce spatiotemporal overlap with wild pigs to avoid competition (Garabedian et al, 2023; Perez Carusi et al, 2017). Examining shared space use between invasive wild pigs and other wildlife is therefore a key step in identifying where competition may occur or what strategies animals adopt to reduce competition.…”

Comparison of daily activity patterns across seasons using GPS telemetry and camera trap data for a widespread mammal

“…In addition to climate and landscape factors, species interactions may also influence behavior and shape daily activity patterns (Dykstra et al, 2023; Garabedian et al, 2023). For example, in Big Cypress National Preserve, a protected area where hunting is prohibited, wild pigs were almost exclusively active during daylight and were inactive at night, which could be related to avoiding predation risk by Florida panthers (Prat‐Guitart et al, 2020).…”

Landscape Use and Activity Patterns of Feral Swine on Rangelands in North Texas

“…Many studies indicate that swine temporal activity is largely based on human pressure, with nonhunted swine often exhibiting more movement during daylight hours (Graves 1984; Podgórski et al 2013; Gray et al 2020). However, a variety of other factors, including seasonality, temperature and precipitation patterns, sex, age, and location and availability of food, among other variables, have been reported to influence the diurnality versus nocturnality of swine activities (Campbell and Long 2010; Kay et al 2017; Clontz et al 2021; Garabedian et al 2023). These variables may be just as important as human pressure in determining swine diel activity patterns (Keuling and Massei 2021).…”