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A study by NTU Singapore and the Smithsonian Tropical Research Institute has found that wild pigs, which wreak havoc in some rainforest ecosystems where they forage and uproot plants, can also help to maintain the biodiversity of these habitats.
Wild pigs are abundant in forests without predators, where they are considered pests. Under these conditions, excessive trampling and foraging by pigs negatively impact vegetation.
Another vegetation-destroying behaviour of pigs is when mother pigs build nests made of hundreds of tree seedlings to give birth in. While this reduces the vegetation in the undergrowth, the researchers hypothesised that tree diversity could be affected if pigs choose specific nesting locations or harvested specific tree species.
To assess the impact of pigs on their native habitats, the team tagged more than 30,000 tree seedlings in a Malaysian rainforest. They then recovered and examined more than 1,800 of those tree tags from more than 200 pig birthing nests to find out how tree diversity changed in the areas where pigs nested.
The researchers found that pigs tend to build their nests in dense seedling patches that are dominated by a single prolific tree species, disproportionately killing more locally common trees.
As a result, there was a higher diversity of plants in areas with pig nests.
“You could consider pigs ‘accidental forest gardeners’ that prune common tree seedlings for their nests, and inadvertently maintain diversity,” said Dr Matthew Luskin, a former research fellow of NTU’s Asian School of the Environment, who led the study.
“Our study is the first to link wildlife disturbances to the underlying ecological mechanisms for maintaining hyper-diverse rainforests.”
“While pigs may contribute to diversity, these findings must be viewed in context,” added co-author Dr Stuart Davies, who is an Adjunct Professor at NTU’s Asian School of the Environment and Director of the Smithsonian Institute’s ForestGEO programme.
“One has to remember, the abundance of wild boars in a number of Asian forests is dramatically reducing tree regeneration and perhaps even the composition of plants in these forests. This may have long-term deleterious consequences for Asian rainforests.”
The researchers are currently investigating if pigs are also important contributors to biodiversity in other Asian forests where they are native, as well as in Australia, where they are an invasive species.
The study “Wildlife disturbances as a source of conspecific negative density-dependent mortality in tropical trees” was published in The Proceedings of the Royal Society B (2021), DOI: 10.1098/rspb.2021.0001.