Mistletoe is a parasitic plant that most people think is only useful for triggering Christmas kisses and as an ingredient in magic strength potion from Ancient Gaul. But recently published research suggests that it plays a crucial role in its ecosystem.
Professor David Watson and Matthew Herring of Charles Sturt University set out to test whether mistletoe is a keystone species – that’s an organism that appears insignificant but actually has a large effect on other species. The best way to test whether a species is a keystone is to remove it from an ecosystem and see what happens. However, that’s usually not only extremely difficult, but risks causing irreparable damage.
In this case though, it’s possible to remove mistletoe without damaging their host trees. After obtaining the necessary permissions, the researchers and teams of volunteers spent two years removing 46 tonnes of mistletoe – predominantly Amyema miquellii, known as either Box, Stalked or Drooping Mistletoe – from 17 woodland sites in the southern Riverina region of New South Wales. They then waited another three years before returning to compare the changes with 11 control sites and 12 where mistletoe was naturally missing.
As predicted, the absence of mistletoe affected the local bird population, with a third of species missing after only 3 years. But what was surprising was that the birds affected weren’t those that nested or fed in mistletoe, but instead it was the insect-eaters. Watson believes that this is because mistletoe drops more leaf litter than its host tree, so its removal takes away the habitat for the insects on which the birds feed.
This study is believed to be the first test of a keystone plant, and the most rigorous ever test of any keystone. Its unexpected outcome demonstrates the subtle dependencies that can exist in ecosystems, and how a single species may do more than you think.
Reference: Watson DM & Herring M 2012, “Mistletoe as a keystone resource: an experimental test”, Proceedings of the Royal Society B: Biological Sciences, vol. 279, no. 1743, pp. 3853-3860 (doi: 10.1098/rspb.2012.0856)