Sugar is an ant’s best friend? Testing food web theory predictions about trophic position and abundance in an invasive ant (Nylanderia fulva)
2022
Kjeldgaard, MacKenzie K. | Sword, Gregory A. | Eubanks, Micky D.
Classical food web theory predicts that species at the base of food webs will be more abundant than those at the top. Likewise, it’s hypothesized that feeding at lower trophic positions (e.g., deriving more nitrogen from plant-based resources such as nectar or honeydew) plays an important role in the establishment, spread, and ecological dominance of invasive social insects. We tested the relationship between diet, abundance, and resource dominance using the invasive tawny crazy ant (Nylanderia fulva). We used stable isotope analysis, pitfall sampling, and attraction of ants to baits to investigate tawny crazy ant trophic position, abundance, foraging intensity, and competition with other ant species at sites across Texas, USA. Tawny crazy ant abundance varied from zero to > 1000 ants per pitfall trap depending on site and month. Counter to our predictions, however, there was no significant relationship between tawny crazy ant abundance and trophic position. Moreover, tawny crazy ant foraging activity and numerical dominance at baits were significantly higher when ants occupied a higher trophic position. Tawny crazy ants were much more predaceous than expected, as worker [Formula: see text]¹⁵N values were often statistically indistinguishable from known arthropod predators (14/22 total observations). A review of the literature indicates that our results add to a growing body of evidence (15/24 studies) suggesting that ant abundance does not always correspond with a more herbivorous diet. Rather, other factors such as dietary flexibility and abiotic features may play a more important role in invasive ant abundance, particularly in the case of tawny crazy ants.
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