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Green Islands - nutrition not predation -an alternative hypothesis
1School of Applied Science, Riverina-Murray Institute of Higher Education, 2850, Wagga Wagga, N.S.W., Australia.
Oecologia
|March 18, 2017
Summary
Red ants protect mountain birch trees from moth larvae by killing them or by improving soil conditions around their nests. This creates "green islands" of healthy trees during pest outbreaks.
Area of Science:
- Ecology
- Forestry
- Entomology
Background:
- Mountain birch forests in Finnish Lapland face defoliation by Operophtera autumnata moth larvae during outbreaks.
- Red ant nests are observed as "green islands" where birch trees survive outbreaks.
Purpose of the Study:
- To investigate the mechanisms behind the survival of mountain birch trees around red ant nests during moth outbreaks.
- To test two competing hypotheses: direct predation of larvae by ants versus ant-mediated soil improvement.
Main Methods:
- Field observations in Finnish Lapland.
- Comparative analysis of birch trees near and far from ant nests.
- Assessment of larval survival rates and tree health indicators.
Main Results:
- Ants directly kill O. autumnata larvae found on nearby trees.
- Trees near ant nests exhibit reduced stress and are less suitable as a food source for larvae.
- Significantly fewer young O. autumnata larvae survive on trees in the vicinity of ant nests.
Conclusions:
- Red ants play a dual role in protecting mountain birch trees from O. autumnata outbreaks.
- Ants act as direct predators of moth larvae and indirectly by enhancing the microenvironment around their nests.
- The "green island" phenomenon is a result of both ant predation and improved soil conditions.
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