Potential landscape connectivity for invasive wild pigs (Sus scrofa) across the northern prairies of North America

Kramer C.J., Boudreau M.R., Miller R.S., Powers R., VerCauteren K.C., Brook R.K.

Resource selection informs understanding of a species’ ecology and is especially pertinent for invasive species. Since introduced to Canada, wild pigs ( Sus scrofa Linnaeus, 1978) remain understudied despite recognized negative impacts on native and agricultural systems globally. Elsewhere in North America, pigs typically use forests and forage in agricultural crops. We hypothesized Canadian wild pigs would behave similarly, and using GPS locations from 15 individuals, we examined diel and seasonal resource selection and movement in the Canadian prairie region. Forests were predominately selected during the day, while corn ( Zea mays L.), oilseeds, and wheat ( Triticum aestivum L.) were predominately selected at night. Forests and corn were consistently selected throughout the growing season. Wetlands and forests showed greater use rates than other habitats, with evident trade-offs as crop use increased with the timing of maturation. Activity was consistent with foraging in growing crops. Results indicate diel patterns were likely a function of short-term needs to avoid daytime anthropogenic risk, while seasonal patterns demonstrate how habitats that fill multiple functional roles — food, cover, and thermoregulation — can be optimized. Understanding selection by invasive species is an important step in understanding their potential environmental impacts in novel environments and informs their management.

Street G.M., Potts J.R., Börger L., Beasley J.C., Demarais S., Fryxell J.M., McLoughlin P.D., Monteith K.L., Prokopenko C.M., Ribeiro M.C., Rodgers A.R., Strickland B.K., Beest F.M., Bernasconi D.A., Beumer L.T., et. al.

Sample size sufficiency is a critical consideration for estimating resource selection functions (RSFs) from GPS-based animal telemetry. Cited thresholds for sufficiency include a number of captured animals and as many relocations per animal N as possible. These thresholds render many RSF-based studies misleading if large sample sizes were truly insufficient, or unpublishable if small sample sizes were sufficient but failed to meet reviewer expectations. We provide the first comprehensive solution for RSF sample size by deriving closed-form mathematical expressions for the number of animals M and the number of relocations per animal N required for model outputs to a given degree of precision. The sample sizes needed depend on just 3 biologically meaningful quantities: habitat selection strength, variation in individual selection and a novel measure of landscape complexity, which we define rigorously. The mathematical expressions are calculable for any environmental dataset at any spatial scale and are applicable to any study involving resource selection (including sessile organisms). We validate our analytical solutions using globally relevant empirical data including 5,678,623 GPS locations from 511 animals from 10 species (omnivores, carnivores and herbivores living in boreal, temperate and tropical forests, montane woodlands, swamps and Arctic tundra). Our analytic expressions show that the required M and N must decline with increasing selection strength and increasing landscape complexity, and this decline is insensitive to the definition of availability used in the analysis. Our results demonstrate that the most biologically relevant effects on the utilization distribution (i.e. those landscape conditions with the greatest absolute magnitude of resource selection) can often be estimated with much fewer than animals. We identify several critical steps in implementing these equations, including (a) a priori selection of expected model coefficients and (b) regular sampling of background (pseudoabsence) data within a given definition of availability. We discuss possible methods to identify a priori expectations for habitat selection coefficients, effects of scale on RSF estimation and caveats for rare species applications. We argue that these equations should be a mandatory component for all future RSF studies.

Hemmingmoore H., Aronsson M., Åkesson M., Persson J., Andrén H.

The conservation of wide-ranging species presents challenges in a world of intensified human land use, forcing animals to occupy and recolonize human-modified landscapes. Although identifying suitable habitat and ensuring connectivity are important in supporting natural recolonization, these actions are rarely validated due to difficulties in monitoring such events. In Sweden, the Eurasian lynx (Lynx lynx) is now recolonizing its former range, after centuries of persecution. We investigated resource selection based on telemetry data from 108 lynx monitored over 20 years. We assessed the differences between the established population in central Sweden and the recolonizing population in southern Sweden, and between established and dispersing individuals. We found that models based on central Sweden successfully identified core habitat patches for establishment in southern Sweden, validated after recolonization. We also found that lynx selected for higher habitat suitability during the recolonization phase, and that dispersing individuals were less selective than established lynx. Using cost-distance analysis, we assessed connectivity between central and southern Sweden, and found that landscape permeability was higher when based on dispersing lynx compared to established lynx. Altogether, our findings suggest that when landscapes are sufficiently similar between source and recolonization areas, resource selection information from an established population can be useful for managers seeking to facilitate recolonization of wide-ranging species. We recommend more frequent use of validation during and after recolonization events, to improve our common understanding of habitat suitability and connectivity modeling, and therefore to enable more active management of recolonization events.

Aschim R.A., Brook R.K.

Invasive species can spread rapidly at local and national scales, creating significant environmental and economic impacts. A central problem in mitigation efforts is identifying methods that can rapidly detect invasive species in a cost-effective and repeatable manner. This challenge is particularly acute for species that can spread over large areas (>1 million km2). Wild pigs (Sus scrofa) are one of the most prolific invasive mammals on Earth and cause extensive damage to agricultural crops, native ecosystems, and livestock, and are reservoirs of disease. They have spread from their native range in Eurasia and North Africa into large areas of Australia, Africa, South America, and North America. We show that the range of invasive wild pigs has increased exponentially in Canada over the last 27 years following initial and ongoing releases and escapes from domestic wild boar farms. The cumulative range of wild pigs across Canada is 777,783 km2, with the majority of wild pig distribution occurring in the Prairie Provinces. We evaluate eight different data collection and evaluation/validation methods for mapping invasive species over large areas, and assess their benefits and limitations. Our findings effectively map the spread of a highly invasive large mammal and demonstrate that management efforts should ideally rely on a set of complementary independent monitoring methods. Mapping and evaluating resulting species occurrences provide baseline maps against which future changes can be rapidly evaluated.

Perry G.L., Lee F.

Metapopulation persistence depends on connectivity between habitat patches. While emphasis has been placed on the spatial dynamics of connectivity, much less has been placed on its short‐term temporal dynamics. In many terrestrial and aquatic ecosystems, however, transient (short‐term) changes in connectivity occur as habitat patches are connected and disconnected due, for example, to climatic or hydrological variability. We evaluated the implications of transient connectivity using a network‐based metapopulation model and a series of scenarios representing temporal changes in connectivity. The transient loss of connectivity can influence metapopulation persistence, and more strongly autocorrelated temporal dynamics affect metapopulation persistence more severely. Given that many ecosystems experience short‐term and temporary loss of habitat connectivity, it is important that these dynamics are adequately represented in metapopulation models; failing to do so may yield overly optimistic‐estimates of metapopulation persistence in fragmented landscapes.

Lewis J.S., Corn J.L., Mayer J.J., Jordan T.R., Farnsworth M.L., Burdett C.L., VerCauteren K.C., Sweeney S.J., Miller R.S.

To control invasive species and prioritize limited resources, managers need information about population size to evaluate the current state of the problem, the trend in population growth through time, and to understand the potential magnitude of the problem in the absence of management actions. This information is critical for informing management actions and allocating resources. We used two national-scale data sets to estimate historical, current, and future potential population size of invasive wild pigs (Sus scrofa; hereafter wild pigs) in the United States. Between 1982 to present, the Southeastern Cooperative Wildlife Disease Study mapped the distribution of wild pigs in the United States. In addition, recent research has predicted potential population density of wild pigs across the United States by evaluating broad-scale landscape characteristics. We intersected these two data sets to estimate the population size of wild pigs in 1982, 1988, 2004, 2010, 2013, and 2016. In addition, we estimated potential population size if wild pigs were present at equilibrium conditions in all available habitat in each state. We demonstrate which states have experienced recent population growth of wild pigs and are predicted to experience the greatest population increase in the future without sufficient management actions and policy implementation. Regions in the western, northern, and northeastern United States contain no or few wild pig populations, but could potentially support large numbers of these animals if their populations become established. This information is useful in identifying regions at greatest risk if wild pigs become established, which can assist in prioritizing management actions aimed at controlling or eliminating this invasive species across broad to local scales.

Paolini K.E., Strickland B.K., Tegt J.L., VerCauteren K.C., Street G.M.

Background The spatiotemporal distribution of resources is a critical component of realized animal distributions. In agricultural landscapes, space use by generalist consumers is influenced by ephemeral resource availability that may produce behavioral differences across agricultural seasons, resulting in economic and production consequences and increased human-wildlife conflict. Our objective was to assess changes in habitat selection across seasons in an invasive generalist omnivore (feral pigs, Sus scrofa). Hypothesizing that pig space use is primarily driven by forage availability, we predicted strong selection for the most nutritionally beneficial crops and resource types as agricultural seasons progressed. We deployed GPS collars on 13 adult feral pigs in the Mississippi Alluvial Valley to study resource selection in a fragmented agricultural landscape. We estimated resource selection using mixed-effect logistic regression to assess variation in selection across planting, growing, harvest, and fallow seasons. Results We found that feral pigs varied resource selection across seasons, particularly for corn (Zea mais). We also detected seasonal dependencies in proportional coverage on the net probability of selection of a land unit (e.g., selection was generally strongest for locations composed of both agricultural and natural habitat), resulting in marked variation in predicted space use among agricultural seasons. Conclusions These findings indicate behavioral changes in selection across agricultural seasons are driven by complex interactions between the availabilities of temporally dynamic resources and temporally static natural cover. Temporal variations in resource selection trends indicate seasonal responses to crop phenology which suggests a season-specific habitat functional response.

Tabak M.A., Webb C.T., Miller R.S.

Population dynamics of species that are recently introduced into a new area, e.g., invasive species and species of conservation concern that are translocated to support global populations, are likely to be dominated by short-term, transient effects. Wild pigs (Sus scrofa, or wild boar) are pulsed-resource consumers of mast nuts that are commonly introduced into new areas. We used vital rate data (i.e., survival and fecundity) for wild pigs in Germany under varying forage conditions to simulate transient population dynamics in the 10-years following introduction into a new environment. In a low forage environment (i.e., conditions similar to their native range), simulated wild pig populations maintained a stable population size with low probability of establishment, while in environments with better quality forage (i.e., conditions similar to parts of their invasive range), high juvenile fecundity and survival facilitated rapid population growth and establishment probability was high. We identified a strategy for simulating population dynamics of species whose reproduction and survival depend on environmental conditions that fluctuate and for predicting establishment success of species introduced into a new environment. Our approach can also be useful in projecting near-term transient population dynamics for many conservation and management applications.

Mangipane L.S., Belant J.L., Hiller T.L., Colvin M.E., Gustine D.D., Mangipane B.A., Hilderbrand G.V.

Garza S.J., Tabak M.A., Miller R.S., Farnsworth M.L., Burdett C.L.

Wild pigs (Sus scrofa) are among the most widespread and destructive invasive mammals in the world. Understanding the spatial ecology of this species is foundational to effectively mitigating further range expansion. We compiled size estimates of home ranges of wild pigs from 30 locations worldwide and modeled the relationship between home-range size and both abiotic (evapotranspiration, latitude, precipitation, and temperature) and biotic (vegetation productivity and mammal species richness) environmental factors. Size of home ranges varied markedly, ranging from 0.62 to 48.3 km2 . Mammal species richness was positively correlated with home-range size and was the only predictor in the best model; other abiotic factors typically correlated with richness, i.e., latitude and evapotranspiration, were not significant predictors of wild pig home-range size. Despite indicating correlation rather than cause, our analyses were conducted at the scale of the home range and therefore may support the invasion paradox hypothesis for mammals, which states that biotic interactions have a greater influence on invasive species at finer spatial scales. While we do not suggest that mammal species richness can preclude populations of wild pigs from continuing to spread in their native or non-native ranges, our correlative results suggest that areas with a diverse mammal community may be more resistant to invasion. This finding supports the intrinsic value of conserving native species and highlights the need for future work exploring the specific mechanisms by which species richness and biodiversity can influence the ecology of invasive species.

Gantchoff M.G., Belant J.L.

Landscape connectivity is vital for species conservation in human-modified landscapes, lessening population declines and genetic depression caused by habitat loss and fragmentation. We used concepts from electronic circuit theory to identify potential areas for American black bears ( Ursus americanus ) that facilitate connectivity between key federally protected areas, determined if black bears used higher quality habitat than available, and examined their distribution relative to human disturbance. We developed a regional (Mississippi, Louisiana, eastern Texas, Arkansas, and Missouri, USA) model estimating landscape resistance to movement using GIS-based features considered to affect black bear space use: land cover type, distance to major rivers, road density, and highway presence. We selected national forests and national wildlife refuges as patches among which to model potential movement. Using citizen-reported black bear sightings from Mississippi and Missouri, we evaluated land cover selection at fine and coarse scales, and validated our model comparing current density between bear sightings and random locations. Black bear sightings occurred in areas of higher current density compared to random locations ( p

Persico E., Sharp S., Angelini C.

Michel N.L., Laforge M.P., Van Beest F.M., Brook R.K.

Understanding source dynamics of invasive species is crucial to their management. Free-ranging wild pigs (Sus scrofa) have caused considerable ecological and agricultural damage throughout their global range, including Canada. Objectives were to assess the spatial and temporal patterns in domestic wild boar and test the propagule pressure hypothesis to improve predictive ability of an existing habitat-based model of wild pigs. We reviewed spatiotemporal patterns in domestic wild boar production across ten Canadian provinces during 1991–2011 and evaluated the ability of wild boar farm distribution to improve predictive models of wild pig occurrence using a resource selection probability function for wild pigs in Saskatchewan. Domestic wild boar production in Canada increased from 1991 to 2001 followed by sharp declines in all provinces. The distribution of domestic wild boar farms in 2006 improved the fit and predictive ability of the habitat-based model, and the number of boar farms in adjacent rural municipalities had a relative variable importance of 0.84. Our results support the propagule pressure hypothesis, which states that establishment success is linked to source dynamics. Although eradication of wild pigs is rarely feasible after establishment over large areas, effective management will depend on strengthening regulations and enforcement of containment practices for Canadian domestic wild boar farms. Initiation of coordinated provincial and federal efforts to implement population control procedures for established wild pig populations are urgently needed to limit the spread of wild pigs and their impacts, and should focus on areas with existing or historic domestic wild boar farms.

Miller R.S., Sweeney S.J., Slootmaker C., Grear D.A., Di Salvo P.A., Kiser D., Shwiff S.A.

Cross-species disease transmission between wildlife, domestic animals and humans is an increasing threat to public and veterinary health. Wild pigs are increasingly a potential veterinary and public health threat. Here we investigate 84 pathogens and the host species most at risk for transmission with wild pigs using a network approach. We assess the risk to agricultural and human health by evaluating the status of these pathogens and the co-occurrence of wild pigs, agriculture and humans. We identified 34 (87%) OIE listed swine pathogens that cause clinical disease in livestock, poultry, wildlife, and humans. On average 73% of bacterial, 39% of viral, and 63% of parasitic pathogens caused clinical disease in other species. Non-porcine livestock in the family Bovidae shared the most pathogens with swine (82%). Only 49% of currently listed OIE domestic swine diseases had published wild pig surveillance studies. The co-occurrence of wild pigs and farms increased annually at a rate of 1.2% with as much as 57% of all farms and 77% of all agricultural animals co-occurring with wild pigs. The increasing co-occurrence of wild pigs with livestock and humans along with the large number of pathogens shared is a growing risk for cross-species transmission.

Drake J.C., Griffis-Kyle K.L., McIntyre N.E.

Biodiversity in arid regions is usually concentrated around limited water resources, so natural resource managers have constructed artificial water catchments in many areas to supplement natural waters. Because invasive species may also use these waters, dispersing into previously inaccessible areas, the costs and benefits of artificial waters must be gauged and potential invasion- and climate change-management strategies assayed. We present a network analysis framework to identify waters that likely contribute to the spread of invasive species. Using the Sonoran Desert waters network and the American bullfrog (Lithobates catesbeianus)—a known predator, competitor, and carrier of pathogens deadly to other amphibians—as an example, we quantified the structural connectivity of the network to predict regional invasion potential under current and two future scenarios (climate change and management reduction) to identify waters to manage and monitor for invasive species. We identified important and vulnerable waters based on connectivity metrics under scenarios representing current conditions, projected climate-limited conditions, and conditions based on removal of artificial waters. We identified 122,607 km2 of land that could be used as a buffer against invasion and 67,745 km2 of land that could be augmented by artificial water placement without facilitating invasive species spread. Structural connectivity metrics can be used to evaluate alternative management strategies for invasive species and climate mitigation.

Giglio R.M., Bowden C.F., Brook R.K., Piaggio A.J., Smyser T.J.

AbstractGlobalization has led to the frequent movement of species out of their native habitat. Some of these species become highly invasive and capable of profoundly altering invaded ecosystems. Feral swine (Sus scrofa × domesticus) are recognized as being among the most destructive invasive species, with populations established on all continents except Antarctica. Within the United States (US), feral swine are responsible for extensive crop damage, the destruction of native ecosystems, and the spread of disease. Purposeful human‐mediated movement of feral swine has contributed to their rapid range expansion over the past 30 years. Patterns of deliberate introduction of feral swine have not been well described as populations may be established or augmented through small, undocumented releases. By leveraging an extensive genomic database of 18,789 samples genotyped at 35,141 single nucleotide polymorphisms (SNPs), we used deep neural networks to identify translocated feral swine across the contiguous US. We classified 20% (3364/16,774) of sampled animals as having been translocated and described general patterns of translocation using measures of centrality in a network analysis. These findings unveil extensive movement of feral swine well beyond their dispersal capabilities, including individuals with predicted origins >1000 km away from their sampling locations. Our study provides insight into the patterns of human‐mediated movement of feral swine across the US and from Canada to the northern areas of the US. Further, our study validates the use of neural networks for studying the spread of invasive species.