How Leaf-Cutting Ants Impact Forests: Drastic Nest Effects on Light Environment and Plant Assemblages

• Published in: Oecologia Vol. 162; no. 1; pp. 103 - 115
• Main Authors: Corrêa, Michele M., Silva, Paulo S. D., Wirth, Rainer, Tabarelli, Marcelo, Leal, Inara Roberta
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer 01.01.2010; Springer-Verlag; Springer Nature B.V
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Ants; Ants - physiology; Atta; Behavior, Animal; Biological and medical sciences; Biomedical and Life Sciences; Canopies; Chrysophyllum; Colonies; Ecological function; Ecology; Ecosystem; Ecosystems; Forest insects; Forest regeneration; Forestry; Forests; Formicidae; Fundamental and applied biological sciences. Psychology; Gaps; General aspects; General forest ecology; Generalities. Production, biomass. Quality of wood and forest products. General forest ecology; Herbivores; Hydrology/Water Resources; Insect colonies; Insect nests; Leaf cutting ants; Leaves; Life Sciences; Light effects; Linear Models; Nesting Behavior; Nests; Plant Animal Interactions – Original Paper; Plant Sciences; Planting density; Plants; Recruitment; Saplings; Sapotaceae - physiology; Seed germination; Seedlings; Seeds; Species richness; Trees; Tropical rain forests; Understory; South America; Brazil; America; Ecosystem engineers; Brazilian Atlantic forest; Plant recruitment; Canopy gaps; Atta cephalotes; Formicidae; Forests; Insecta; Formicoidea; Canopy gap; Recruitment; Arthropoda; Light; Atlantic Façade; Environment; Hymenoptera; Invertebrata; Nest; Community; Ecosystem engineer; Aculeata
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-009-1436-4

Leaf-Cutting ants (Atta spp.) have become a topical issue in Neotropical ecology, particularly because they are reaching hyper-abundance due to escalating levels of fragmentation in recent years. Yet, despite intensive research on their role as dominant herbivores, there is still insufficient documentation on the impacts of their large, long-lived nests on plant assemblage structure and ecosystem functioning. Our study aimed at investigating the magnitude, nature, and spatial extent of nest influence by assessing 11 attributes of ant nest, canopy structure, light environment and sapling assemblage for 20 colonies in four plots along nest-understorey gradients in a large remnant of Atlantic forest. We also monitored the performance of seeds and seedlings of Chrysophyllum viride, an abundant shade-tolerant species. Previously unrecognized canopy gaps above ant nests (0.04-87.9 m²) occurred in 95% of all colonies surveyed. Overall, canopy openness and light availability at least doubled in ant nest plots compared with distant understorey plots. These drastic changes in the light environment paralleled those in plant assemblage: sapling density almost tripled (mean ± SE: 0.42 ± 0.1 saplings m⁻²) and sapling species richness doubled (0.16 ± 0.02 species m⁻²) in distant plots, as did shade-tolerant species. After a 1-year period, only 33 ± 15.6% of the seeds germinated and all seedlings died on nests, whereas seed germination reached 68 ± 5.1% in distant plots and 66.4 ± 7.6% of their seedlings survived after 12 months. Therefore, plot location was the most significant explanatory variable for predictable and conspicuous changes in the light environment and structure of sapling assemblages. Our findings greatly extend knowledge on the role played by leaf-cutting ants as ecosystem engineers by demonstrating that ant nest-mediated disturbance promotes environmental modifications in tens of meters around nests and is thus, strong enough to drive plant recruitment and consequently alter both the floristic and functional signature of plant assemblages.