Invasive ants reduce abundance of small rainforest skinks

Lori Lach,Dylan Case,Conrad J Hoskin,Peter Yeeles

doi:10.1007/s10531-022-02360-6

Abstract

Invasive ants are among the world’s most damaging invasive species, often directly or indirectly affecting native fauna. Insecticidal baits are the main method for suppressing or eradicating invasive ant populations, but their use must be considered against potential for unintended effects on native organisms. The invasive yellow crazy ant (Anoplolepis gracillipes) is widespread in the tropics, particularly on islands, where they have displaced a range of invertebrates. Effects of this ant on vertebrates, and in continental ecosystems generally, are less studied. We investigated the effects of yellow crazy ants and bait application on rainforest skinks and their invertebrate prey. We compared skink and skink prey abundance across four replicated rainforest site categories: high and low yellow crazy ant sites had both been baited but differed in yellow crazy ant activity; control sites had never had yellow crazy ants or been baited; and buffer sites had never had yellow crazy ants but had been baited. We recorded significantly lower abundance of two small skink species (Lygisaurus laevis and Saproscincus tetradactylus) in high yellow crazy ant sites compared to all other site categories. The differences persisted even after baiting reduced yellow crazy ant activity by 97.8% ± 0.04% (mean ± SD). A larger rainforest skink species (Carlia rubrigularis) was not negatively affected by yellow crazy ant invasion. Skink prey abundance was significantly lower in high yellow crazy ant sites compared to control sites and low yellow crazy ant sites, but not compared to buffer sites. These differences did not persist following baiting. We found no evidence that baiting negatively affects skinks or their invertebrate prey. Our data suggest that yellow crazy ants, but not the bait used to treat them, pose a direct threat to small rainforest skinks.

Highlights

Invasive ants are a threat to conservation in many parts of the world because they can alter the composition and functioning of ecosystems
381 records were of C. rubrigularis and 260 were of the smaller skinks L. laevis (199 sightings) and S. tetradactylus (61 sightings)
None of the juvenile small skinks were observed in high yellow crazy ant sites, and about half of them (9/19 for L. laevis, and 4/8 for S. tetradactylus) were observed in control sites

Summary

Introduction

Invasive ants are a threat to conservation in many parts of the world because they can alter the composition and functioning of ecosystems. Most of the documented effects of invasive ants on native invertebrate species are considered direct and are attributed to the high abundance invasive ants achieve (Holway et al 2002). The importance of indirect effects of invasive species is becoming more widely recognized in invasion ecology (Northfield et al 2018; White et al 2006). Indirect effects are those that are mediated through one or more additional species. Indirect effects of invasive ants are more difficult to discern but may be no less significant in their consequences for native species and ecosystem function. Low invertebrate abundance associated with red imported fire ants (Solenopsis invicta) resulted in low survival of juvenile endangered Attwater’s prairie chickens (Tympanuchus cupido attwateri) (Morrow et al 2015)

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Conclusion