Invasive Species

Contributed Paper
ROOM: Room 220 – Ruidoso

1:10PM Genetic Origins of United States Feral Swine Populations
Timothy J. Smyser; Michael S. Robeson; Hendrik-Jan Megens; Mirte Bosse; Martien A.M. Groenen; Samuel R. Paiva; Danielle A. de Faria; Harvey D. Blackburn; Brandon S. Schmit; Antoinette J. Piaggio
Feral swine (Sus scrofa) are a long-established invasive species in the United States with populations established in the 1200s in Hawaii and mid-1500s on the mainland. Despite their long history, feral swine remained restricted to the southeast, California, and Hawaii until the 1980s but have since expanded dramatically with populations now established in >40 states. We used molecular tools to gain a greater understanding of the origins of both historic and newly emerging populations and elucidate the processes driving range expansion. Specifically, we used principal component analysis to compare high density single nucleotide polymorphism genotypes (29,383 loci) of 3436 feral swine sampled across the invaded US range to a comprehensive reference set of 2968 domestic pigs and wild boar, representing 152 distinct genetic groups sampled throughout the world. Historic populations were genetically intermediate to US/European pigs and European wild boar, consistent with the documented history in which feral populations were established through the release of domestic pigs and subsequently augmented with wild boar to improve hunting appeal. Newly emerging populations in Michigan, Colorado, and Indiana had a far higher wild boar genetic composition than historic populations, suggesting swine collected from novel sources were used in the establishment of these populations. Populations across the Hawaiian Islands and Guam represented a mix of Asian and US/European ancestry, reflective of establishment with Polynesian colonization and interbreeding with US/European pigs from the time of first European contact in 1778 onward. This work has demonstrated that natural range expansion, translocation from historic populations, and releases from novel genetic sources have contributed to the expansion of this ecologically destructive and economically costly invasive species. Future work with genetic clustering algorithms will allow us to increase the precision in which we can quantify genetic composition and will improve our ability to identify the sources of new populations.
1:30PM Biotic and Abiotic Factors Predicting the Global Distribution And Population Density of an Invasive Large Mammal
Jesse Lewis; Matthew Farnsworth; Chris Burdett; David Theobald; Miranda Gray; Ryan Miller
Biotic and abiotic factors are increasingly acknowledged to synergistically shape broad-scale species distributions. However, the relative importance of biotic and abiotic factors in predicting species distributions is unclear. In particular, biotic factors, such as predation and vegetation types, including those resulting from anthropogenic land-use change, are underrepresented in species distribution modeling, but could improve model predictions. Our goal was to understand the contribution of biotic and abiotic factors in predicting population density of an invasive large mammal with a global distribution. To evaluate our research objectives, we used the wild pig (Sus scrofa) as our focal species, which is one of the most destructive invasive species globally and is currently undergoing an unprecedented global range expansion. Using generalized linear models and model selection techniques, we used 129 estimates of wild pig population density from five continents to (1) evaluate the relative importance, magnitude, and direction of biotic (i.e., vegetation and predation) and abiotic (i.e., climate) factors in predicting population density and (2) create a predictive map of wild pig population density across the world. Incorporating diverse biotic factors, including those resulting from human land-use change, into species distribution modeling substantially improved model results. Population density of wild pigs was driven by both biotic and abiotic factors, including potential evapotranspiration, large carnivore richness, precipitation during the wet and dry seasons, unvegetated area, and agriculture. The predictive map of population density revealed wide-ranging potential for an invasive large mammal to expand its distribution across all continents. This information can be used to proactively create conservation/management plans to control the spread of this invasive species. Our study demonstrates that the ongoing paradigm shift, which recognizes that both biotic and abiotic factors shape species distributions across broad scales, can be advanced by incorporating diverse biotic factors, including predation and human land-use change.
1:50PM Do Common Forest Management Techniques Facilitate Exotic Plant Invasions?
Donald P. Chance; Johannah R. McCollum; Garrett M. Street; Bronson K. Strickland; Marcus A. Lashley
Invasive plant species share several traits, such as production of large amounts of viable seed with long range dispersal capabilities, that potentially allow them to invade following disturbances. Thus, because higher levels of invasive plants often impede management objectives, understanding the effects of common management techniques on exotic plant invasions is important for managers. In this study, we evaluated the effects of different timber thinning regimes (9, 14, and18 m2/ha) paired with other common wildlife habitat management practices (fire and a broadleaved selective herbicide) on percent coverage of invasive species in the understory. We used a systematic sampling design to collect data at 81 locations across a 200-ha loblolly pine (Pinus taeda) stand crossing thinning level with fire and paired fire and herbicide applications. Coverage of invasive species was highest in stands treated with thinning only followed by the coupled disturbance of thinning and fire with herbicide application. Basal area had no effect on the coverage of invasive species. Our results indicate a threshold in disturbance intensity where thinning and burning provide resistance to exotic species invasions in comparison to thinning only or more intensive disturbances coupling thinning and fire with herbicides. Wildlife habitat managers should consider the likelihood of exotic plant invasions when determining the intensity of forest management regimes for southern pine forests. Because some herbicides are selective, further research evaluating different types of herbicides is needed, particularly when exotic plants have already invaded.
2:10PM What If Everything You Thought You Knew About “Feral” Cats Was Wrong?
Peter J. Wolf
Among the many topics discussed under the broad category of “invasive species,” few are as contentious as the management of unowned free-roaming cats (Felis catus). Like any public policy, the policies intended to effectively manage the population of these cats must, in addition to meeting other criteria (e.g., reflect broad public interest, economic feasibility, etc.), be based on sound science. Although many communities across the country have implemented programs based on the trap-neuter-vaccinate-return (TNVR) method of managing “feral” cats, such efforts are often met with significant opposition by those claiming to have science on their side. Careful scrutiny of the studies typically cited in support of these claims, however, reveals a troubling pattern of careless research design and methods, flawed analyses, and dubious conclusions. Public policy justified by such work is likely to prove costly and ineffective, and will very likely increase any legitimate threats unowned free-roaming cats pose to wildlife, the environment, and public health. In this presentation, I will: (1) examine one of the most-often cited research papers on the subject, (2) offer compelling evidence to challenge its key assertions, and (3) argue that policies opposing TNVR actually exacerbate the threats to wildlife, the environment, and public health.
2:30PM Impacts of Invasive Mute Swans on the Avian Diversity of Great Lakes Coastal Wetlands
Nicole J. Wood; Thomas M. Gehring; Donald G. Uzarski
< Mute swans (Cygnus olor) are an invasive species from Eurasia that have been introduced several times to North America (Allin et al., 1987; Ciaranca et al., 1997). The mute swan population has steadily increased in the Great Lakes Basin at a rate of 10-18% annually, that before recent increases in management action, resulted in a Michigan population estimated at 15,500 individuals in 2010 (Petrie & Francis, 2003; MDNR, 2012). Mute swans commonly are the largest waterfowl present in Great Lakes coastal wetlands and their aggressive nature toward native birds, combined with their tremendous consumption of submerged aquatic vegetation, may impact the diversity of native bird populations (Bellrose, 1976; Allin & Husband, 2003). 15 minute avian point-count surveys were conducted during the breeding season, May 20 - July 10, throughout the Great Lakes Basin beginning in 2011, as part of a greater Great Lakes Coastal Wetland Monitoring Program. Two surveys at each point were obtained, with one morning survey and one evening survey. The surveys sampled on both the audio and visual spectrum with passive listening bookending broadcast calls of threatened or endangered wetland species. The Shannon-Weaver index was calculated for each coastal wetland site. Survey locations with no mute swan presence, were compared to sites with mute swans presence to detect any differences in native bird species diversity. Invasive mute swans have the ability to impact Great Lakes coastal wetlands in a multitude of ways and by assessing the diversity of the native birds in these habitats, we can further tease apart the full impact of this invasive species.>
2:50PM Refreshment Break
3:20PM Comparing Depredation by Feral Swine between Simulated and Natural Turkey Nests
Heather N. Sanders; Nathan P. Snow; David G. Hewitt; Kurt C. Vercauteren; Humberto L. Perotto-Baldivieso
Feral swine (Sus scrofa) are a prolific invasive species whose continuing range expansion throughout North America has severe economic and ecological implications. Surprisingly little is known about the foraging strategies and extent of feral swine damage relative to ground-nesting birds despite reports of nest depredation for species such as the wild turkey (Meleagris gallopavo). The objectives of this study were to analyze the role of nest density in the predation of nests by feral swine and to quantify the extent of nest depredation by feral swine relative to other predators. We deployed artificial wild turkey nests within the available nesting habitat in the home ranges of collared feral swine using 3 treatment levels: control (i.e., no nests), low nest density, and high nest density. We also monitored natural turkey nests to assess the effect of the presence of the hen on depredation rates. Feral swine depredated the highest proportion of nests, followed by native nest predators such as raccoons (Procyon lotor) and gray foxes (Urocyon cinereoargenteus). These results indicate that feral swine seasonally exploit available food sources like the eggs of ground-nesting birds. This study provides further evidence that feral swine are a detrimental invasive species to an important game species and sensitive ground-nesting bird in the United States.
3:40PM Quantifying Site-Level Elimination Certainty of an Invasive Species Through Occupancy Analysis of Camera-Trap Data
Amy Davis; Ryan McCreary; Jeremiah Psiropooulos; Gary Brennan; Terry Cox; Andrew Partin; Kim Pepin
Efficient implementation of elimination programs for invasive species depends on accurate monitoring to determine when lack of detection indicates true elimination; which is particularly difficult as animals at low densities are often difficult to detect. Common management-based monitoring approaches (e.g., camera traps) can be used for guiding surveillance and control priorities, and inferring elimination certainty where individuals have not been observed (negative surveillance). We demonstrate our method using dynamic occupancy to monitor changes in the distribution of an invasive species, feral swine (Sus scrofa), based on camera-trap data from June 2014-January 2016 in San Diego County, California. We assessed detection probability and used that information to demonstrate how the certainty of local (site-level) absence could be estimated in areas with negative surveillance data using an occupancy framework and Bayes Theorem. Site usage of feral swine declined overall. The most informative predictors of site usage were spatial (latitude and longitude). Site-level extinction rates increased over time and in response to management removal efforts; and site-level colonization rates were heavily impacted by having neighboring sites that were used. Our framework provides a means for using management-based monitoring data to quantify certainty of site-level absence of an invasive species, allowing for adaptive prioritization of monitoring resources. Our approach is flexible for application to other species and types of monitoring (e.g., track-plates, eDNA).
4:00PM Monitoring the Eradication of European Mouflon Sheep from the Kahuku Unit of Hawai‘I Volcanoes National Park
Steven C. Hess; Seth W. Judge; Jonathan K. Faford; Dexter Pacheco; Christina R. Leopold
European mouflon (Ovis gmelini musimon), the world’s smallest wild sheep, have proliferated throughout the Hawaiian Islands including native forests within Hawai‘i Volcanoes National Park (HAVO) and degraded fragile native ecosystems through browsing, bark stripping, and trampling. HAVO resource managers initiated ungulate control efforts in the 469 km2 Kahuku Unit shortly after it was acquired in 2003. We monitored eradication effort with aerial surveys, intensive ground surveys, and camera traps to detect the last remaining animals in a 25.9 km2 fence-enclosed unit. More than 4,860 mouflon were removed from 2004 to 2016. Aerial shooting yielded the most removals per unit effort but ground methods yielded more removals overall. Ground shooting with dogs, intensive aerial shooting, ground sweeps, and forward-looking infrared (FLIR) assisted shooting were necessary to find and remove the last remaining mouflon. The Judas technique, baiting, and trapping were not successful at attracting or detecting small numbers of remaining individuals. Effort expended to remove each sheep increased several-fold during the last three years of eradication effort. Complimentary active and passive monitoring techniques allowed us to track the effectiveness of effort and reveal the locations of remaining mouflon groups. Seven systematic aerial surveys over an 11-year period were used to index population decrease from a maximum of 782 in 2004. There were no detections from aircraft after the fenced unit was enclosed in 2012, although 829 mouflon were subsequently removed. In contrast, 48 mouflon were recorded by camera traps from 2014–2016 while 125 were removed from the unit. The effort and variety of methods required to eradicate mouflon from an enclosed unit of moderate size illustrates the difficulty of scaling up to the entire population.
4:20PM Do Feral Swine Alter the Island Biogeography of Native Wildlife in Agro-Ecosystem Forest Patches?
Matthew R. Ivey; Dr. Marcus Lashley; Dr. Bronson K. Strickland; Dr. Michael E. Colvin
Island biogeography theory has successfully explained the relationship between species richness and habitat area in a variety of fragmented landscapes including agro-ecosystems. However, no experiments have evaluated how invasive species affect island biogeography relationships with native species. Generalist invasive species may alter the small-island effect if the effective patch size (i.e., usable space) is greater for generalists than specialized species. Moreover, if generalist invasive species sustain higher densities because of differences in effective patch size, the resulting increase in competition may affect native species accumulation in relation to area. To test these hypotheses, we evaluated the effects of feral swine (Sus scrofa) on the small-island effect and the species-area relationship of native wildlife in forest patches interspersed within agricultural areas of the Mississippi Alluvial Valley. Using paired opposing camera traps (1 pair per 20 hectares) in 16 forest patches 8 – 470 hectares in size, we determined occupancy of swine and native wildlife species. Swine occupied six of the sampled patches, ranging from 28 to 470 hectares in size. Swine presence indicates change in directionality of the small-island effect. However, the species-area relationship had a steeper relationship (0.37 slope with swine: 0.31 without swine) with area when swine were present (i.e., after patch size exceeded the small-island effect threshold). This increase in slope indicates that native wildlife were accumulated more quickly up to the 20 species detected in patches 313-470 hectares. The presence of feral swine can have a significant effect on the island biogeography of native wildlife in agroecosystems, particularly in smaller patch sizes. Landscape planning to increase semi-natural plant community patches in agro-ecosystems should take into consideration the presence or absence of feral swine when determining the minimum patch size to accomplish objectives.
4:40PM Spatiotemporal Drivers of Habitat Selection by Feral Pigs in an Agricultural Landscape
Kelsey Paolini; Garrett M. Street; Bronson K. Strickland; Jessica L. Tegt; Kurt C. VerCauteren
Studying distributional patterns of wildlife aids in the understanding of how spatiotemporal variation in dynamic landscapes contributes to changes in species resource selection. Evaluating spatiotemporal changes in resource selection provides valuable information about the fundamental drivers of space use. Feral pigs (Sus scrofa) are extreme generalists capable of occupying numerous landscapes and cause detrimental damages particularly within agricultural regions, which therefore requires understanding resource use. Fifteen adult feral pigs were fitted with Iridium GPS collars in the Mississippi Alluvial Valley to study resource selection in a fragmented, agricultural landscape. We conducted Resource Selection Analyses using mixed effect logistic regression with random intercepts for each individual to assess variation in crop selection across agriculturally defined seasons (i.e., planting, growing, harvest, and fallow). Our analyses generally indicated dependencies in proportional coverage on the net probability of selection of a resource unit (e.g. as the probability of selecting proportional coverage by corn increased, the amount of proportional wetlands increased). At a finer temporal scale, we detected changes in the direction of selection for certain resources changed as a function of day and night, particularly for corn. These findings suggest that behavioral changes in selection across seasons are driven by a complex interaction between temporally dynamic pulsed resource availability and temporally static natural habitat. Our results can be used to create season-specific maps of likely habitat selection, which can help direct managers to areas where feral pigs have higher probabilities of landscape use to improve efficiency and efficacy within each season. Our models additionally improve our ecological understanding of pig space use patterns within pulsed resource agricultural landscapes.


Contributed Paper
Location: Albuquerque Convention Center Date: September 26, 2017 Time: 1:10 pm - 5:00 pm