Collapse of an Ant-Scale Mutualism in a Rainforest on Christmas Island

Positive interactions play a widespread role in facilitating biological invasions. Here we use a landscape--scale ant exclusion experiment to show that widespread invasion of tropical rainforest by honeydew-producing scale insects on Christmas Island (Indian Ocean) has been facilitated by positive i...

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Bibliographic Details
Published in:Oikos 2007-07, Vol.116 (7), p.1238-1246
Main Authors: Abbott, Kirsti L., Green, Peter T.
Format: Article
Language:English
Subjects:
Animal populations
Anoplolepis
Ants
Barringtonia racemosa
Ecological invasion
Ecosystems
Forest canopy
Forest insects
Formicidae
Insect colonies
Insects
Lac
Mutualism
Nonnative species
Rainforests
Scale insects
Social insects
Syzygium
Tropical rain forests
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Summary:Positive interactions play a widespread role in facilitating biological invasions. Here we use a landscape--scale ant exclusion experiment to show that widespread invasion of tropical rainforest by honeydew-producing scale insects on Christmas Island (Indian Ocean) has been facilitated by positive interactions with the invasive ant Anoplolepis gracilipes. Toxic bait was used to exclude A. gracilipes from large (9-35 ha) forest patches. Within 11 weeks, ant activity on the ground and on trunks had been reduced by 98-100%, while activity on control plots remained unchanged. The exclusion of ants caused a 100% decline in the density of scale insects in the canopies of three rainforest trees in 12 months (Inocarpus fagifer, Syzygium nervosum and Barringtonia racemosa), but on B. racemosa densities of scale insects also declined in control plots, resulting in no effect of ant exclusion on this species. This study demonstrates the role of positive interactions in facilitating biological invasions, and supports recent models calling for greater recognition of the role of positive interactions in structuring ecological communities.
ISSN:0030-1299
1600-0706
DOI:10.1111/j.2007.0030-1299.15629.x