Introduced fire ants can exclude native ants from critical mutualist-provided resources
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Animals frequently experience resource imbalances in nature. For ants, one resource that may be particularly valuable for both introduced and native species is high-carbohydrate honeydew from hemipteran mutualists. We conducted field and laboratory experiments: (1) to test if red imported fire ants (Solenopsis invicta) competed with native ants for access to mutualisms with aphids, and (2) to quantify the effects of aphid honeydew presence or absence on colony growth of native ants. We focused on native dolichoderine ants (Formicidae, Dolichoderinae) because they are abundant ants that have omnivorous diets that frequently include mutualist-provided carbohydrates. At two sites in the southeastern US, native dolichoderine ants were far less frequent, and fire ants more frequent, at carbohydrate baits than would be expected based on their frequency in pitfall traps. A field experiment confirmed that a native ant species, Dorymyrmex bureni, was only found tending aphids when populations of S. invicta were suppressed. In the laboratory, colonies of native dolichoderine ants with access to both honeydew and insect prey had twice as many workers and over twice as much brood compared to colonies fed only ad libitum insect prey. Our results provide the first experimental evidence that introduced ants compete for access to mutualist-provided carbohydrates with native ants and that these carbohydrates represent critical resources for both introduced and native ants. These results challenge traditional paradigms of arthropod and ant nutrition and contribute to growing evidence of the importance of nutrition in mediating ecological interactions.
KeywordsSolenopsis invicta Dolichoderinae Mutualism Invasive species Honeydew
Funding was provided by National Science Foundation DEB 0716983 to M.D.E., DEB 0717054 to D.A.H. and DEB 0716966 to A.V.S. We thank M. Buckman for field assistance in Alabama and Michael Castro for assistance with laboratory work. We thank B. Stadler and two anonymous reviewers for helpful comments on a previous draft of this manuscript. All experiments complied with current US laws.
Conflict of interest
The authors declare that they have no conflict of interest.
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