Research into Invasive Species: The Wild Boar

According to the National Invasive Species Information Center, an invasive species is a plant, animal or other organism that is nonnative to the ecosystem under consideration and whose introduction causes or is likely to cause harm (Leeper, 2017). There are many invasive species which fall under categories of plants, insects, and wildlife. I chose to research the invasive species called the wild boar also referred to as wild pig or feral hog and in scientific terms is called the sus scrofa. The sus scrofa is a large pig like species with a large, powerful body covered in coarse hair fur. They have thick neck, long head and a protruding snout which aids in food hunting. Their lean and muscular shape, short hind legs and very long tusks and snouts allows us to easily distinguish the sus scrofa species from the regular domestic pigs which have smaller features described. The hair of a sus scrofa is long and coarse and sometimes forma a mohawk along their back whereas, the domestic pig hair is shorter and softer and grows equally everywhere (Global Invasive Species Database, Species Profile: Sus Scrofa, 2019). Another physical observation is the difference in their tails. Domestic pigs have curly tails which is very different to the sus scrofa that is seen to have a long straight tail with a bushy end. As a sus scrofa gets older, to aid in protection during fights, they develop a thick, fury shield covering their shoulders. The sus scrofa is an omnivorous species that eat a wide array of food and will eat almost anything from plants to eggs or even birds (Global Invasive Species Database, Species Profile: Sus Scrofa, 2019). Boars can vary greatly in color and size. Colors can vary from brown to black, blonde, red, yellow, stripped and sometimes even spotted. Brown and black boars are more common to see and a mature wild boar can weigh between one hundred and thirty pounds to one hundred and fifty pounds (Global Invasive Species Database, Species Profile: Sus Scrofa, 2019). Boars may seem pretty small compared to other wildlife species, however they can have many negative impacts such as damaging our landscape, our wildlife, water quality, diseases and because they have the highest reproduction rate amongst ungulates around the world (Saez-Royuela, 1986). Because of their ability to reproduce in great numbers consistently this means that the population of Wild Boar (Sus scrofa) will be able to spread over miles and miles and will continue to expand if they are not halted or controlled in some way and will continue to destroy and consume our natural resources and wildlife which has an impact on human life as well. 

Wild Boars are nonnative to America and are actually a native mammalian species of Western Europe and Northern Africa (Dobson, 1998). Boar population in the past have been seen to have fluctuated frequently, some populations have died out, other populations have flourished (Scandura M. L., 2008). Presently, population growth is expanding rapidly as compared to 1975, where the population densities began to level off (Saez-Royuela, 1986). Post-glacial expansion explains much of the increase in Wild Boar population, in other words, there has been very little human intervention (Scandura M. L., 2008). Wild Boars’ characteristics allow them to inhabit a wide range throughout Europe, and are a terrestrial animal with the largest range in Europe (Dobson, 1998). The broad range of the species of the Wild Boar is a result of its non-specific diet, as well as its large litter size.

The European Wild Boar, in 1925, was imported to Monterey County in California, for hunting and interbred with feral hogs that had been brought in 1769 by Spanish explorers as a food source and to aid with clearing land. The sus scrofa was first seen at Pinnacles National Park in the late 1960s (Wild Pigs- Pinnacles National Park, 2019). This invasive species has over the years spread vastly over California and have been seen in other states such as Hawaii, Mexico, Canada, Texas, Louisiana, and Oklahoma. This occurred both naturally and in some cases with the help of landowners and hunters who force them to migrate from place to place  (Wild Pigs- Pinnacles National Park, 2019).

The unlimited diet of the Wild Boar also means that they are not restricted to live in any specific region or location (Schley, 2003). Wild pigs consume an abundance of plant matter including grasses, forbs, berries, roots, and bulbs. They also feed on ground dwelling insects, worms, reptiles, amphibians, fish, small mammals, and carrion including other pigs (Wild Pigs- Pinnacles National Park, 2019). They will consume anything in their path, invertebrates, small mammals and other small vertebrates, eggs of ground-nesting birds, even the young of larger animals such as white-tailed deer. In addition, feral swine compete with native wildlife for valuable resources, such as acorns that squirrels, deer, and turkey depend on during winter month (Wild pig, Sus scrofa (feral type) Linnaeus, n.d.). In a study, this non-specific diet was documented for the Wild Boars found in Sardinia. They were found to have up to 19 different plant species in their stomachs when their gastric content was examined. Plants such as Castanea sativa, Ceratonia sili- qua, Chamaerops umilis, Cichorium intybus, Hordeum sativum, Juniperus oxycedrus, Myrtus communis, Olea europea, Pirus amygdaliformis (Pinna, 2007). Not only was vegetation found in the animals’ stomachs, but Wild Boar were also found to have three additional categories of food in their stomach: insect larvae, hairs of mammals, and feathers of birds  (Pinna, 2007). The versatility shown in their diet allows the wild boar species to have little to no problem migrating to different areas of the world that have drastically different arrays of vegetation and wildlife.

Similar to their unique ability to adapt to different diets, the rate of reproduction also changes depending on location. Where there is a change in latitude of its location, there is also a change in the numbers seen in a litter (Bywater, 2010). An observation was found stating that an increase of 0.15 piglets per degree, or one piglet for every 6.6° increase in latitude has been discovered in the species (Bywater, 2010). An assumption made for this reproduction fluctuation was in connection with food consumption during the various times of the year. During winter there are higher latitudes as compared to other seasons like summer. Where there are higher latitudes, food is unstable therefore resulting in lower reproduction numbers. Where there is constant food source, reproduction increases resulting in an overall larger litter size. A state of equilibrium occurs in lower latitudes because the food supply of the Wild Boar remains constant  (Bywater, 2010).

There are several negative impacts of the Wild Boar on our agriculture and plants, wildlife, soil, and quality of water, all caused by their feeding, wallowing, rooting, and tree rubbing. As mentioned earlier, Wild Boars have an unlimited diet and because they eat anything this creates a new competitor for many other wildlife creatures that have the same or common diet such as acorns.  Although Wild Boar are causing a wide range of problems for multiple areas in the United States, they are excessively threatening the environment of the Great Smokey Mountains National Park in Tennessee (Bratton, 1974), as well as Oak Woodlands of California (Wilcox, 2009) . Wild Boar have negative impacts on the agricultural plots of certain areas within the United states (Massei, 2004). They have also begun to threaten particular plant species due to damaging the land, as well to act as predators towards various types of vertebrates (Wilcox, 2009). Wild Boars compete with native wildlife for valuable resources, such as acorns that squirrels, deer, and turkey depend on during winter month (Wild pig, Sus scrofa (feral type) Linnaeus, n.d.).

Rooting by Wild Boar destroys not only plant life but also the habitats of many living animals and organisms. They use their strong necks, wedged head and long snouts to uproot the soil in order to get food.  As the soil is uprooted, it now becomes susceptible to the radiant heat waves the sun emits causing it to dry. Plants now struggle to find water to grow. This results in a decrease in native plants allowing exotic or invasive plants to make their homes. This leads to a loss in the balance of natural plant life which impacts not only animals but also humans as we have a reduced number of plant life and species. Apart from rooting, Wild Boar, eat a variety of fruits, nuts, and seeds which all aid in germination and fertilization. In other words, plants get less nutrition if any at all, after the feeding of the Boar. This affects our agricultural sector negatively as the producers and consumers are all impacted.

The impact Wild Boar has on wildlife very much resembles its impact on plant life as its consumption of food such as acorns, and insects also competes with other wildlife like deer. Additionally, Wild Boar not only compete but prey on many other species that may threaten their ability to flourish and, in some cases, makes them extinct. Another effect of loss of life of wildlife is the fact that Wild Boar have the ability to transmit many diseases such as plague, Q Fever, Pseudorabies (PRV), Porcine Reproduction and Respiration Syndrome (PRRS), Tularemia, and Brucellosis, all of which are transmitted to wildlife but a fair amount can still be transmitted to humans (Gaskamp, n.d.).

The Wild Boar contributes to soil erosion by again their habit of rooting. They usually tend to root near river banks which causes soil to lose and wash away when rain falls. This creates poor quality water as they become polluted with soil from the washed away banks (Wild Pigs- Pinnacles National Park, 2019). Poor water quality not only negatively impacts aquatic life like the California red-legged frog, which is already a threatened species, but also human life as we have a reduced source of clean water for consumption (Wild Pigs- Pinnacles National Park, 2019).

Many attempts have been made to control the Wild Boar such as poisoning, a combination of poisoning and hunting and also snaring. There has not been much motivation to completely eradicate the entire population as they benefited many such as Captain Cook who used the pig in trading with the natives as early as 1777. Also, in central Europe the false spruce webworm (Cephalcia abietis) causes defoliation of Norway spruce trees an in the case of high densities of boars they were able to cause high mortality to insect larvae by up to 70%, however they also cause damage to tree roots making the perceived benefit negligible (Global Invasive Species Database, Species Profile: Sus Scrofa, 2019). In the agricultural sector, pigs are of a benefit as they help with harvest season, removing remaining sweet potato tubers and turn and aerate the soil before replanting (Global Invasive Species Database, Species Profile: Sus Scrofa, 2019). Wild Boar is also a common food source for many hunters and because many simply don’t see the need to terminate all the species and actions such as poisoning although cost-effective was not as beneficial as hunting. Additionally, the chemical products used to poison the Boar was almost counteractive as the compounds used were toxic to many species having an unintended impact on other species. The lack of effort of research and careful eradication study is the reason why failure keeps occurring and the inability to visualize and understand the danger of the Boar also adds to this (Global Invasive Species Database, Species Profile: Sus Scrofa, 2019).

In conclusion, the Wild Boar (Sus scrofa), is a very versatile species, able to adapt, survive and reproduce in almost any territory due to its’ unending dietary components.  The Wild Boar has many negative impacts such as damage to agriculture and plants, wildlife, soil, and quality of water, far outweighing the benefits of the species. Because there are so many negative impacts and unsuccessful efforts to control the population, the government should take initiative and invest into the study and campaign of successful eradication of the species or proper control methods to save our environment from a loss of natural native species varying from plants to wildlife. By doing this we benefit ourselves, the human race, as we protect ourselves from diseases, loss of natural resources, and a variety of crops and plant life that create food sources for us and also aids in medicine research and creation.

Bibliography

• Bratton, S. (1974). The effect of the European Wild Boar (Sus scrofa) on the High-Elevation Vernal Flora in Great Smoky Mountains National Park. Bulletin of the Torrey Botanical Club 101(4):198-206.
• Bywater, K. M. (2010). Litter size and latitudein a large mammal: the Wild Boar Sus scrofa. Mammal Review 40(3) 212-220.
• Dobson, M. (1998). Mammal Distributions in the Western Mediterranean: the role of human intervention. Mammal Review 28(2):77-88.
• Gaskamp, J. (n.d.). Feral hogs present disease risk for livestock and people. Retrieved from Noble Research Institute: https://www.noble.org/news/publications/ag-news-and-views/2015/march/feral-hogs-present-disease-risk-for-livestock-and-people/
• Global Invasive Species Database, Species Profile: Sus Scrofa. (2019, November 26). Retrieved from Global Invasive Species Database (2019): http://www.iucngisd.org/gisd/species.php?sc=73
• Leeper, C. (2017, March 2). 5 Resources on Invasive Species. Retrieved from Noble Research Institute: https://www.noble.org/blog/invasive-species-resources/
• Massei, G. a. (2004). The environmental impact of Wild Boar. Galemys 16:135-145.
• Pinna, W. G. (2007). Vegetable and animal food sorts found in Sardinian Wild Boar (Sus scrofa meridionalis). Journal of Animal Physiology and Animal Nutrition 91:252-255.
• Saez-Royuela, C. a. (1986). The increas population of Wild Boar (Sus Scrofa) in Europe. Mammal Review 16(2):97-101.
• Scandura, M. L. (2008). Ancient vs. recent processes as factors shaping the genetic variation of the European Wild Boar.
• Scandura, M. L. (2008). Ancient vs. recent processes as factors shaping the genetic variation of the European Wild Boar: are the effects of the last glacier still detectable? Molecular Ecology 17:1745-1762.
• Schley, L. a. (2003). Diet of Wild Boar (Sus scrofa) in Western Europe, with particular reference to consumption of agricultural crops. Mammal Review 33(1):43-56.
• Wilcox, J. T. (2009). Wild pigs as predators in Oak Woodlands of California. Journal of Mammalogy 90(1):114-118.
• Wild pig, Sus scrofa (feral type) Linnaeus. (n.d.). Retrieved from Center for Invasive Species and Ecosystem Health: https://www.invasive.org/browse/subinfo.cfm?sub=3874
• Wild Pigs- Pinnacles National Park. (2019). Retrieved from National Park Service: https://www.nps.gov/pinn/learn/nature/wildpigs.htm