Researchers from the University of Illinois and the University of California at San Diego have uncovered one secret to the ant’s success: dietary flexibility. The insects can live high on the hog, but will eat at lower levels of the food chain if they have to.
Chadwick V. Tillberg and colleagues studied an invasion of ants across a canyon in Chula Vista, Calif., over eight years. They collected ants at various sites and analyzed the ratio of stable nitrogen isotopes in the insects, an indication of what they were eating.
As the researchers report in The Proceedings of the National Academy of Sciences, ants right at the invasion front showed higher levels of nitrogen-15, suggesting they were consuming native ants and other insects. But as the front moved on, nitrogen-15 levels declined, with the ants switching to food from plants, particularly the honeydew produced by aphids.
The researchers also compared isotope levels between ants in California and in their native range in Argentina. They found that the native ants ate higher on the food chain.
Taken together, the researchers say, the findings support the idea that a flexible diet makes for a successful invasion. What’s unclear is precisely why the dietary switch occurs. It may be forced upon the ants once they’ve munched through the other ant species in their territory. Or it may simply be that Southern California, with its citrus industry, has so many honeydew-producing aphids around for the ants to exploit.
