Wild pigs have huge impact on biodiversity

Hawaii conservationists know well the far-reaching impact of wild pigs on the environment. The non-native species is notorious for rambling through the forest as herbivore, top predator and ecosystem engineer, digging and rooting in the soil to help transform the natural landscape.

A team of researchers from the University of Hawaii at Manoa and Royal Melbourne Institute of Technology University in Australia has found that wild pigs have a huge impact on biodiversity around the world but perhaps none greater than on islands.

As it turns out, Polynesia was the most threatened region globally with nearly 20% of all species affected by wild pigs, the study found.

The findings were published in the journal Scientific Reports following a multiyear effort combing through data in the International Union for Conservation of Nature’s Red List of Threatened Species.

“We found that in addition to the over 300 plant species threatened by wild pigs globally, wild pigs actively predate and destroy critical nesting sites for hundreds of threatened and endangered reptiles, amphibians and birds,” said lead author Derek Risch, a wildlife spatial planner in the Hawaii Wildlife Ecology Lab in UH’s Department of Natural Resources and Environmental Management.

In total, wild pigs were found to threaten 672 species in 54 countries across the globe. Most of these taxa are listed as critically endangered or endangered, and 14 species have been driven to extinction as a direct result of impacts from wild pigs.

That puts feral pigs up there with some of the word’s most problematic species with similar global distribution, including feral cats, rodents, mongooses and wild dogs.

“I’m hoping to draw more attention to the global impact of wild pigs,” Risch said, adding that those impacts are actually poorly understood in comparison with some of the other invasives.

The researchers found that wild pigs affect similar numbers of species in both North America and Europe despite the fact that pigs are native to Europe and considered invasive to North America.

But island endemic species are particularly vulnerable, according to the study, especially plants, reptiles and amphibians.

Risch said islands evolved without similar omnivores, and they have a propensity to host higher densities of pigs that cause all kinds of environmental havoc in the wild.

Pigs, or puaa, were brought to Hawaii by the Polynesians many centuries ago. Capt. James Cook brought European breeds in the late 1700s, which were released into the wild, and it eventually made the Hawaiian pigs bigger.

Today the puaa continues to make for outstanding hunting, but natural-resource managers are erecting fences and taking other measures to prevent the pigs from further degrading the landscape. Hunters and land managers often work together, but conflicts have been known to erupt.

Risch, who also has been modeling the distribution of hoofed animals across Hawaii, said the study highlights the importance of different groups working together to come up with solutions for managing the wild pigs.

“Hunters are essential,” he said. “They play a crucial role in managing the pigs.”

The study found that wild pigs rank close to feral cats in terms of the number of species affected, despite a well-deserved reputation regarding cats as the most detrimental invasive predator to island ecosystems.

A previous assessment, according to the paper, had identified 175 species threatened by feral cats on islands, while the latest study found that wild pigs threaten at least 131 species (63 reptiles, 65 birds, three mammals).

Given the role of wild pigs as both a top predator and destructive herbivore, their additional threats to plant and invertebrate taxa make them a serious cause for concern and indicate major ecosystem-level impacts, the study said.