Ecological Profile: Wild Boar, Sus scrofa
Wild boar, Sus scrofa, also known as the eurasian wild pig or wild swine are versatile and resilient creatures which can thrive and adapt in a variety of habitats. Originating in Western Europe, Southeast Asia, and Northern Africa, they have been introduced to a variety of other locations due to human intervention, both intentionally (to be used in agriculture) and inadvertently (Pastick, 2014). Wild Boar are currently found on every continent other than Antarctica, and have become common throughout Eurasia and parts of North America (Wickline, 2014).
Figure 1. Wild boar world distribution, highlighted by the beige areas. Map: R. Moore, ArcMap 10.4 (Oliver, & Leus, 2008).
Prior to the 2013 study, completed by Brook and van Beest, there had been very little research on wild boars in Canada, leaving the distribution, feeding and nesting habits, any associated risks specific to Canada relatively unknown. Wild boar abundance has drastically increased in western Canada, and populations are now considered invasive, even with methods such as unrestricted hunting numbers have not been seriously affected Canada (Brook & van Beest 2013). Thus far, boar sightings have been sparse in Ontario.
Figure 2. Wild boar sightings in Ontario, 2014. Map: R. Moore, ArcMap 10.4 (Wild Boar Canada, 2017).
Wild boar can survive in a variety of habitats because they have a highly variable diet and do not depend on specific elements to subsist (Pastick, 2014). They are very adaptive, which speaks to their success and increasing species dispersion. While wild boar rely mostly on vegetation, they are considered omnivores (Pastick, 2014) and as such, are not limited in habitat by the presence of any specific plant or organism. From temperate and subtropic areas, wild boar can be found in grassy savanna areas, wooded forests, agricultural areas, shrublands and marshy swamplands (Wickline, 2014) and tend to avoid regions facing temperature extremes, lacking in water or substrates that do not allow for rooting and foraging (Wickline, 2014).
Female wild boar tend to live in groups ranging in size, usually between 6 to 20 closely related individuals, although groups of up to 100 different species have been documented. Males are polygynous and travel alone, other than during mating season. Mating can take place any time year-round, and is dictated by food/energy availability and the nutritional needs of the females being met (Wickline, 2014). After reaching maturity, female piglets continue to live in groups with their mothers, while males remain only they are 1 to 2 years old, and then leave the herd (Wickline, 2014). Although, wild boar tend to provide less parental care to their piglets (compared to other Sus spp.), they have an increased litter size and a fast rate of maturity (Pastick, 2014). Table 1 demonstrates the reason that Sus scrofa is found to be a K-strategist, with some tendencies towards r-selection compared with other Sus spp.
Table 1. r and K selection. Modified to include Sus scrofa. (Department of Biology, University of Miami, n.d.).
|Characteristic||r – strategist||k – strategist||Wild Boar|
|Mortality||Variable and Unpredictable||More constant and predictable||Not variable nor constant|
|Litter Size||Large||Small||Moderate – 5 to 6 piglets|
|Parental Investment/Care||Very little if any||Required||Offspring need parental care to survive until maturity|
|Frequency of Reproduction||Once to multiple times over a short period of time||Multiple times but over a prolonged period of time||Can produce 2 litters per year if conditions are good|
|Additional Factors||Most reproductively mature individuals reproduce successfully||Few reproductively mature individuals or only some reproduce successfully||Males compete to breed with a group of females (sounders)|
Figure 3. Survivorship curve. (Feltham, 2017).
Wild boar appear to display Type II survivorship (see Figure 1). A study in Western Europe demonstrated that while juvenile mortality averages 15% in the first three months, only 25-50% of wild boar make it beyond the first year of life, and merely 15% of all progeny survive to independence (Oliver & Leus, 2008). The main cause of death varies in by location; for instance, in Europe predation is the main cause of death, while in North America hunting claims a larger proportion, and parasites consistently affect large numbers around the world (Oliver & Leus, 2008).
Dispersal and Vectors:
Wild boars are an invasive species brought over from Europe for domestication and hunting. Wild boar have few barriers with the main one being humans, in creating fences to protect agriculture and hunting areas (McClure et al., 2015). The other, is the effects of environmental factors, which impact the males more than the females. Constant development and habitat loss are major human-imposed limiting factors, causing the dispersal of the wild boar into more and different ecosystems. Migration for wild boars is easy, as they can be very fast runners when need be and cover a lot of land. Rivers and water-bodies are no problem for them, as they are excellent swimmers, so the only barrier is humans blockages (A-z animals, 2017). While searching for food in the forest, and moving among different herbaceous species, many seeds’ spores and pollen is carried by the wild boar`s coarse hair (Heinken et al., 2006).
In many countries, hunting wild boar is entirely unrestricted, and can maintain steady populations despite an annual hunter-kill rate of about 50% (Oliver & Leus, 2008). It is notable that unrestricted hunting has not in most cases served to severely diminish wild boar populations. Wild boar tend to carry numerous parasites and highly contagious diseases (Oliver & Leus, 2008) which can be transferred to domestic pig species.
Outside of their native habitat boars are one of the most destructive invasive species on the planet (National Geographic, 2011). Wild Boars are a threat to human safety, as they can be dangerous if they feel threatened. Males may reach as much as 3 meters in length and weight of over 150 kg. Furthermore, their tusks may be as long as 20 cm. Boars are social animals and tend to reside in groups, saying that, it is likely you will run into more than 1 boar at a time which could make a bad situation even more severe.
Brook[JF1] , Ryan K. & van Beest, Floris M. (2013). Distribution and Risk Perceptions of Prairie Boar. Wildlife Society Bulletin. DOI: 10.1002/wsb.424.
Department of Biology, University of Miami. (n.d.). R and k selection. Retrieved from http://www.bio.miami.edu/tom/courses/bil160/bil160goods/16_rKselection.html
Heinken, T., Schmidt, M., von Oheimb, G., Kriebitzsch, W., & Ellenberg, H. (2006). Soil seed banks near rubbing trees indicate dispersal of plant species into forests by wild boar. Basic and Applied Ecology, 731-44. doi:10.1016/j.baae.2005.04.006. http://ra.ocls.ca/ra/login.aspx?inst=sandford&url=http://search.ebscohost.com.eztest.ocls.ca/login.aspx?direct=true&db=edselp&AN=S1439179105000538&site=eds-live&scope=site
McClure, M. L., Burdett, C. L., Farnsworth, M. L., Lutman, M. W., Theobald, D. M., Riggs, P. D., . . . Miller, R. S. (2015, August 12). Modeling and Mapping the Probability of Occurrence of Invasive Wild Pigs across the Contiguous United States. Retrieved January 27, 2017, from http://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0133771
National Geographic. (September 29, 2011). Facts: Wild Hog Invasion. Retrieved from http://channel.nationalgeographic.com/wild/dangerous-encounters/articles/facts-wild-hog-invasion/
Oliver, W. & Leus, K. 2008. Sus scrofa. The IUCN Red List of Threatened Species 2008:e.T41775A10559847. Retrieved from http://dx.doi.org/10.2305/IUCN.UK.2008.RLTS.T41775A10559847.en.
Pastick, Jillian. (2014). The biology of native and invasive wild boar (Sus scrofa) and the effect it is having in its invasive range. Eukaryon, 8, 60-63. Retrieved from https://www.lakeforest.edu/live/news/1650-the-biology-of-native-and-invasive-wild-boar-sus
Wild Boar Canada. (2017). Wild boar sightings Canada. Retrieved from http://wildboarcanada.ca/#sthash.PNSIagrd.dpbs
Wickline, K. (2014). Sus scrofa. Animal Diversity Web, University of Michigan. Accessed January 23, 2017 at http://animaldiversity.org/accounts/Sus_scrofa/