Question: How does the ant Atta vollenweideri indirectly affect the shrub Grabowskia duplicata? Does environmental modification induced by nest building affect the life history and population structure of this dominant shrub?
Location: Halophytic savanna of western Uruguay, South America.
Methods: We compared the density of three shrub size classes, seedlings, saplings and adults, among patches created by ant nest building and in non‐modified areas. We studied key soil properties for plant growth in both live nests and non‐modified areas. We performed a greenhouse experiment to study the effects of soils (live nest versus non‐modified area) on shrub germination probability. We also assessed vegetative propagation by measuring the incidence of root suckers and clonal offshoots in live nests and non‐modified areas through a field survey.
Results: Seedling‐size class was more abundant on live nests than in non‐modified areas, suggesting that environmental conditions of this type of habitat (i.e. increased sodium and moisture content of soil, and decreased soil compaction) could facilitate shrub recruitment. We did not find any effects of soil type (live nests versus non‐modified areas) on shrub germination probability. However, the vegetative propagation incidence was higher in the environment with live nests.
Conclusions: We found a strong indirect relationship between the ant A. vollenweideri and the shrub G. duplicata. This relationship seems to be mediated by an allogenic engineering process, i.e. soil bioturbation caused by nest building. The environmental conditions of live nests seem to facilitate shrub recruitment, mainly by increasing vegetative propagation.
1. Ants modify soil properties via nest construction and by doing this modulate soil resources for other organisms. In this sense ants are recognised as ecosystem engineers.
2. In this framework, two less well‐studied issues are focused on: (i) the permanence of the effects of ant nests on plant communities after colonies have died, and (ii) the scaling up from patch to landscape‐scale effects.
3. The aim of the present study was to address these issues in the open dry forests of Uruguay, inhabited by the ant Atta vollenweideri Forel. The active and abandoned nests of this ant represent different and conspicuous patches (30–60 m2) in the landscape.
4. The soil concentration of sodium, a key element in the system, was substantially higher among active nests, and remains high during the early stages of abandoned nests. Woody species abundance, richness, and composition were affected at the patch scale, and simulation models suggested an increase in species richness at the landscape scale.
5. The present study highlights the importance of abandoned nests for plant‐species richness in the ecosystem engineer framework and the need to advance in an integrative approach to study both local and landscape effects of ant's nests.
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