Abstract
Ant-aphid mutualism is known to play a key role in the structure of the arthropod community in the tree canopy, but its possible ecological effects for the forest floor are unknown. We hypothesized that aphids in the canopy can increase the abundance of ants on the forest floor, thus intensifying the impacts of ants on other arthropods on the forest floor. We tested this hypothesis in a deciduous temperate forest in Beijing, China. We excluded the aphid-tending ants Lasius fuliginosus from the canopy using plots of varying sizes, and monitored the change in the abundance of ants and other arthropods on the forest floor in the treated and control plots. We also surveyed the abundance of ants and other arthropods on the forest floor to explore the relationships between ants and other arthropods in the field. Through a three-year experimental study, we found that the exclusion of ants from the canopy significantly decreased the abundance of ants on the forest floor, but increased the abundance of beetles, although the effect was only significant in the large ant-exclusion plot (80*60 m). The field survey showed that the abundance of both beetles and spiders was negatively related to the abundance of ants. These results suggest that aphids located in the tree canopy have indirect negative effects on beetles by enhancing the ant abundance on the forest floor. Considering that most of the beetles in our study are important predators, the ant-aphid mutualism can have further trophic cascading effects on the forest floor food web.
Highlights
In addition to predation and competition, mutualism is an important factor in shaping community structure and diversity [1,2]
In the group of ants, 99.9% belonged to L. fuliginosus, with 0.07% belonging to Formica fusca Linnaeus and 0.02% belonging to Formica sinenis
Many studies have found that aphid-tending ants have important impacts on plants and other insects that live on plants [6,7,8], suggesting that aphids can shape the arthropod commu
Summary
In addition to predation and competition, mutualism is an important factor in shaping community structure and diversity [1,2]. Ant-aphid mutualism is a common mutualistic interaction in the field, where ants feed on the honeydew excreted by aphids and in return protect those insects from predators and parasitoids [3,4]. Aphids lead to a high abundance of ants in the tree canopy [5], and aphid-tending ants have important ecological impacts for both the host plant and other related insect species on the plant [6,7,8]. Plant-based food (such as extrafloral nectar and honeydew excreted by aphids) may be a key factor in creating high densities of ants in the field [17,18]. Aphids may enhance the abundance of ants in the canopy as well as on the forest floor. The magnitude of the dependency of ants on aphids is rarely studied, with most existing studies only evaluating the impacts of ants on aphids [3]
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