The critically endangered Roussea flower has been vanishing from Mauritius, an island in the Indian Ocean.
Now scientists have figured out why.
“The blue-tailed gecko is the only pollinator and seed disperser for the flower,” says biologist Dennis Hansen. But alien ants that have invaded the island “have also taken a liking to the flower and are scaring the gecko away.”
It’s a case of an invasive species causing serious disruption to an ancient arrangement between gecko and plant.
The endemic blue-tailed day-gecko Phelsuma cepediana is the sole pollinator and seed disperser of the critically endangered endemic plant Roussea simplex, Hansen, now at Stanford University, and Christine Müller from the University of Zurich, Switzerland, write in a paper published in the current issue of the journal Biotropica.
“The flowers and fruits are often visited by the invasive ant Technomyrmex albipes, which forages on the nectar and fruit pulp, and tends honeydew-producing mealybugs on the fruits,”
the researchers write.
The scientists explored how the presence of the alien ants influence geckos foraging at flowers and fruits of R. simplex by removing and excluding ants from flowers and fruits.
“Gecko visitation rates to ant-free control flowers and fruits, and flowers and fruits where ants had been removed and excluded, were higher than those to ant-infested flowers and fruits,.” they write. The resulting seed set of ant-infested flowers was greatly reduced, compared to ant-free control flowers.”
“Similarly, for fruits with ants, very few seeds were likely to be ingested and dispersed by the geckos.”
Thus, the researchers concluded, the ants monopolize flowers and fruits of R. simplex, and prevent access of pollinating and seed-dispersing geckos by aggressive interference competition.
For a critically endangered plant like R. simplex, “this is of urgent conservation concern,” the researchers noted in their paper. Unless the ants are removed, the Roussea “is going to be in really big trouble in the not too distant future.”