Wild pigs are recognized worldwide as a nuisance to the environment. The IUCN lists them as one of the worst invasive species due to their potential to damage crops, harbor diseases and disrupt ecological processes.
Now, research published in the Journal for Nature Conservation reveals that the expanding presence of wild pigs (Sus scrofa) across South America poses a greater threat to biodiversity hotspots and protected areas than previously believed.
Researchers assessed the species’ suitability ranges at different analytical levels and discovered that a significantly higher number of protected areas are invaded or potentially at risk than shown in previous research. Furthermore, nearly half (44.8%) of wild pig occurrences studied were inside biodiversity hotspots.
In South America, domestic pigs arrived with European settlers, and wild boars were introduced by the Argentinian rancher Pedro Olegario Luro at the beginning of the 20th century for hunting purposes. Over time, the boars have dispersed throughout the continent, interbred with domestic pigs and successfully established populations.
The assessment reveals compelling insights into the vulnerability of specific hotspots in the region. Notably, the Atlantic Forest emerges as the most susceptible, with a remarkable 85% of its total area deemed suitable for wild pigs (meaning habitat that allows them to thrive), followed by Cerrado (61.3%), Chilean Winter Rainfall-Valdivian Forests (37.5%) and tropical Andes (5.6%).
These results raise yet another alert for conservationists to take precautionary measures, since invasive species may cause further damage to wildlife in already threatened areas.
The expansion of wild pigs across South America
Brazilian ecologist Clarissa Alves da Rosa, a researcher at the National Institute for Amazonian Research who was not involved in the study, tells Mongabay in a phone interview, “The increase of boars in Brazil as a whole, and especially in the Atlantic Forest, is associated with the species’ interaction with human beings.”
She explains that invasive species, such as wild pigs, may supplement their diets with human-grown food. And when that happens, she further adds, the wild pig “tends to really increase and expand its population. When we mention a fragmented biome, such as the Atlantic Forest, this supplementary feeding comes from agricultural crops — mainly corn and sugarcane. What happens is that they have the perfect environment — there are forest fragments where they can take shelter and agricultural crops where they can feed.”
She also mentions that another contributing factor to the increased range of the species is that some people, interested in maintaining the boar population, transport and release them to areas where they previously were not present in order to secure hunting permits, as they are the only species permitted to be hunted in Brazil. Regarding this issue, Alves da Rosa mentions, “There is a debate within academia about whether we consider boars as a resource or as a problem.”
She further adds: “If it is considered a resource, there is an interest in maintaining its population because people don’t want this resource to disappear. Even though in terms of public policy and science, we label boars as a problem, we know that the population as a whole sees it as a resource. It ends up being a source of food, and some people enjoy hunting them.”
Impacts on biodiversity
In her Ph.D. studies within Itatiaia National Park, one of Alves da Rosa’s objectives was to explore whether wild pig behavior could replace the beneficial ecological functions provided by peccaries (Tayassuidae family), a social mammal often mistaken for a pig and a threatened species in the region. Through her investigation, she uncovered distinct environmental impacts caused by these two species, despite their similar behavior.
While both wild pigs and peccaries engage in “snouting” the soil, Alves da Rosa observed a significant difference: Wild boars, due to their longer snouts, create larger holes that remove crucial soil layers, akin to plowing the soil. On the contrary, peccaries contribute to the formation of small ponds through their digging activities, which serve as vital breeding sites for some amphibians.
In addition to removing important soil layers, wild pigs are associated with various environmental impacts such as destroying water springs, uprooting native plants and preying on seeds and small invertebrates, according to Alves da Rosa. These examples illustrate the damage that wild pigs may cause in relevant areas for biodiversity conservation and further stress the importance of assessing their potential distribution.
These findings raise particular concern in the Atlantic Forest — the region found to be the most vulnerable to wild pig invasions in the recent study — which is home to more than 20,000 species of plants, including 6,000 endemic species and the highest tree diversity per hectare worldwide. Simultaneously, it has the highest number of threatened and extinct species of any biome in Brazil, as indicated in the recently published report by the Brazilian Institute of Geography and Statistics.
Methods and results
The Journal for Nature Conservation study assessing broad-scale potential distribution of wild pigs in South America involved an international, multidisciplinary team of 17 scientists who used a method called ecological niche modeling by combining records of 6,502 wild pig occurrences, both direct (sightings) and indirect (tracks and camera trapping) over the course of 116 years (1906-2022) with environmental data and information from 278 protected areas.
This approach enabled them to investigate the current and potential dispersion of wild pigs across ecoregions, protected areas and hotspots in South America, specifically encompassing Argentina, Brazil, Uruguay, Paraguay, Chile and Bolivia.
Sixty-eight ecoregions were compared, showing that 41 already had records of wild pigs, while 64 presented suitable or partially suitable conditions to sustain their presence. Only four ecoregions were classified as completely unsuitable, and three of them are cold deserts with extreme weather conditions. These results reflect the high adaptability of pigs to different environments.
The article adds that the relative success of the species in colonizing different habitats can be attributed to their “high reproductive potential,” “highly plastic diet,” “wide climatic and topographic tolerance” and “behavior adaptability under contrasting conditions of human pressure.”
Regarding the protected areas in South America, the study highlighted that the protected landscapes and national parks are at greater risk. While comparing the number of affected areas and the potential risk in each country, Uruguay ranked first in both categories, having all of its protected areas “invaded” by wild pigs.
The results obtained by the researchers differed significantly from previous assessments done in individual countries.
The article states that the potential area of distribution in Argentina was considerably bigger than noted in a 2019 report published on the website Categorización de los Mamíferos de Argentina. Meanwhile, in Chile, the new research finds an estimated potential distribution area of more than 150,000 square kilometers (58,000 square miles), which is much larger than the 27,600 km2 (10,650 mi2) of occupation noted in a 2015 assessment published in the journal Mastozoología neotropical. In Brazil, the pig’s presence was confirmed in 205 previously unreported municipalities, increasing the total number by 17.8%.
Such variations could be explained by the different methodological approaches undertaken and also because of “the inclusion of a large number of new records spanning a longer period of time,” the article states. The authors add that with this new approach, it was also possible to identify places where the species may be present but still undetected.
In addition to the article, Luciano La Sala, the study’s lead author, also made available a dynamic web application with visual representations of the study results that conservationists and policymakers can readily consult.
“We know that biological invasions are better controlled in the earlier stages. When boars are detected in a protected area it is because they already reached a problematic populational level,” explains Alves da Rosa.
This is why assessments of this nature provide important information for protected-area managers, allowing them to take precautionary measures to prevent the establishment of new wild pig populations, thus preventing further loss of critically endangered species in vulnerable areas.
Social and economic impacts
Environmental impact is not the only concern raised by the expansion of these wild pigs. The social and economic impacts are also significant. Alves da Rosa, who also worked with local communities surrounding Itatiaia National Park, mentions that “when we start noticing a meaningful environmental impact, it’s because the social impact is already extensive.”
Rosilene Cosmo Correa, also known as Lena, is a small-scale farmer who grows corn, potatoes and sugarcane and lives in Aiuruoca, a city located in the mountainous Mantiqueira region of the Atlantic Forest — a place surrounded by fields and araucaria (Araucaria angustifolia) forests, some of the pig’s favorite places due to the availability of Brazilian pine nuts (known as pinhão in Portuguese).
In a phone call, Lena describes her first experience dealing with wild pigs back in 2015. “I was cultivating a sugarcane plantation, and I had a dream of buying my first car. I was going to sell this harvest for 8,000 reais (about $1,600).” Within three days of continuous wild pigs attacks, she says, “not even a single sugarcane was left.”
After this episode, Lena started working as a maid to help with her household income. “Since then, I dropped everything and I started going out to work, because there’s no way I can sustain myself on my farm anymore.”
The expansion of wild pigs in the region is provoking drastic changes to the livelihoods of small producers. Since the attacks recur, people feel discouraged to farm and resort more to shopping in supermarkets, explains Lena.
“In the past, we had a lot of things at home. If we have corn here in the fields, we have a lot. We have everything; corn is everything. Cane is also the basis of everything.”
She also talks about the Brazilian pine nut, an important regional product that is getting increasingly difficult to collect since wild pigs quickly consume them.
“The women who didn’t work outside used to pick the pine nuts to sell, you know? A lot of pine nuts were sold and it helped a lot throughout the year, because with that money women could do a lot of things. Now there are no more pine nuts to sell.”
When asked about how people in her community are taking action, she says, “There are a few people who take initiative and say, ‘I’m going to hunt a pig today,’ but they can’t do it, because they have no adequate equipment or training, and they are also afraid [of being attacked by the pigs].”
Davi Andrade Sampaio, who is also a small producer in Aiuruoca, talks in a phone call about the challenges he faces when hunting these wild pigs.
When chasing a pig, a hunter might need to cross different properties and that might result in conflict, explains Davi. He says some landowners are animal rights defenders and are against hunting; in some cases, they might even call the inspectors from the Brazilian Institute of Environment and Renewable Natural Resources. In this scenario, the hunters have to call back the dogs and retreat, he mentions.
Both Davi and Lena, agree on the fact that greater measures must be adopted to control the pigs. They feel that their problem is still broadly unacknowledged and they’re fearful of the future consequences of the rapid dispersion of the pigs in their region.
To effectively manage wild pig populations, a comprehensive understanding of the interplay between protected and rural areas is essential, as wild pigs move and circulate between these two environments. Protected areas provide shelter for wild pigs, while rural areas serve as abundant sources of food for their sustenance. As a result, conservation managers and farmers living near protected areas must coordinate efforts to address this problem.
Challenges and possibilities for wild pig control
According to Alves da Rosa, eradication of wild pigs is utopian, only occurring successfully on islands. To minimize the problem, researchers, managers and local communities must work together, she further explains.
In Brazil, public power lacks the financial, technical and logistic conditions to effectively manage wild boars in protected areas. In such conditions, the burden of this responsibility falls entirely on autonomous hunters. “Protected areas are primarily dedicated to biodiversity conservation, so how do we let hunters within them?” she says.
Alves da Rosa emphasizes that before introducing hunters into protected areas, it is crucial to establish a strong and trustworthy relationship.
Moreover, managing wild boars requires more than just controlling their population within protected areas. It also necessitates effective management in the surrounding areas to ensure comprehensive control measures.
Another concern she raises is the limited budget within protected areas, which often leads managers to prioritize wild boar control only when the situation is already beyond control. Ideally, effective management should be a priority from the early stages of the invasion. Early detection systems and proactive population management would be the ideal approach to address the issue before it escalates. However, the current reality is far from achieving this scenario.
‘Then what happens?’
The presence of wild pigs in South America is turning into a serious concern not just for conservationists but also for people living in rural areas. The expansion of the wild pigs, despite being a recognized international problem, remains largely unsolvable and unacknowledged.
Researchers once again note their potentially damaging impacts on regional biodiversity in already threatened areas such as the Atlantic Forest and Cerrado. Assessments of this kind provide crucial information for managers, scientists, policymakers and conservationists who may reallocate and reinforce their efforts to protect areas at greater risk.
Small farmers find themselves in a difficult spot, being unable to address this issue alone without support from authorities, says Lena. “We are in no position to defend ourselves. Everything we do is as a small producer. So if we don’t have the money and don’t produce, how are we going to do anything? And then what happens? Nothing, right!”
Citations:
La Sala, L. F., Burgos, J. M., Caruso, N. C., Bagnato, C. E., Ballari, S. A., Guadagnin, D. L., … Zalba, S. M. (2023). Wild pigs and their widespread threat to biodiversity conservation in South America. Journal for Nature Conservation, 73, 126393. doi:10.1016/j.jnc.2023.126393
Skewes, O., & Jaksic, F. M. (2015). History of the introduction and present distribution of the european wild boar (Sus scrofa) in Chile. Mastozoología neotropical. Retrieved from http://www.scielo.org.ar/scielo.php?script=sci_arttext&pid=S0327-93832015000100012
This article by Vitor Alexandre Araujo Prado dos Anjos was first published by Mongabay.com on 12 June 2023. Lead Image: A wild pig (Sus scrofa). Image by Nathalie Hausser via Flickr (CC BY-NC-ND 2.0).
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