They say three's a crowd, and that appears to be as true ecologically as it is socially. Researchers have discovered that an invasive ant is ruining the mutualistic relationship that has long existed between a gecko and a critically endangered flower.

The blue-tailed gecko (Phelsuma cepediana) feeds on nectar from the flowers of the Roussea simplex shrub on the island of Mauritius, pollinating the plant and dispersing its seeds.
Geckos
© Dennis HansenGeckos have an essential pollination role with this critically endangered flower.

But the invasive white-footed ant (Technomyrmex albipes) that arrived on the island in the last century has disrupted the gecko-flower relationship. The ant builds galleries of dirt on the flower where it can "farm" other insects to feed on honeydew.

Ecologists Dennis Hansen now at Stanford University, and Christine Müller from the University of Zurich, Switzerland, allowed ants to interact with some flowers and not with others.

They coated some Roussea stalks with grease, preventing ants but not geckos from climbing to the flower. Other plants were left alone.

The pair found that geckos very rarely climbed flowers that had been invaded by ants. They also found that the seed numbers in ant-infested plants was greatly reduced, suggesting that ant presence disrupts both pollination and seed distribution.

Invasive ants are known to be problematic, but breaking the relationship between the flower and the gecko raises the danger to a much higher level, says Hansen. Similar situations on other islands should be closely watched, he says.

See a gallery of photographs of the gecko and its rival for the flowers nectar.

Journal reference: Biotropica, DOI: [link].