The extermination of native ants sets off a ripple effect through an ecosystem. Some native ant species that eat seeds have coevolved with certain native grasses and other plants to become a crucial part of the plant's propagation by carrying the seeds to new areas. Without the native ant species to spread their seeds, the grasses can't flourish. Any significant impact on the plants would also likely affect creatures that feed on or nest in the plants.
Argentine ants have been declared agricultural pests in California because of the damage they do to citrus crops. The invaders are partial to areas where the ground has been disturbed, such as plowed fields and construction sites. They also spread through plants sold by nurseries.
The invaders are agriculturalists after a fashion themselves, tending "herds" of aphids and other scale insects that attach to plants and suck out the sugary sap. The ants, in turn, feed on the sugar-rich liquid that the aphids excrete, "quaintly called honeydew," Gordon said. By protecting the aphids from predators, the Argentines enable the insects to spread.
That yummy honeydew is what brings the Argentine invaders and the winter ants into conflict, as winter ants also tend aphids.
The Stanford students began observing the native ants as part of a 2008 short summer class for sophomores called Ecology of Invasions, taught by Gordon. At a variety of locations on the Stanford campus, they started out simply observing and recording ant behavior while visiting each site at the same time every day.
"We were looking at the nest openings of the winter ants and one day it was just winter ants going about their business foraging for food and making trails just typical ant behavior," said Leah Kuritzky, a student in the class and one of the coauthors of the PLoS ONE paper.
|Contact: Louis Bergeron|