Trophic position and seasonal changes in the diet of the red wood antFormica aquiloniaas indicated by stable isotope analysis

Abstract

1. Red wood ants are among the most numerous generalist predators and strongly affect the composition of arthropod communities in forest ecosystems. However, their trophic position remains poorly understood. Stable isotope analysis was applied to study the trophic position of Formica aquilonia and reveal seasonal changes in its trophic links with both myrmecophilous aphids and other invertebrates in a mixed forest of western Siberia.2. The δ15N values of F. aquilonia exceeded those of herbivores and aphids by approximately 3.5‰. Despite obligate trophobiotic relationships with aphids, F. aquilonia occupied the trophic position of first‐order predator. The higher content of 13C in the worker ants, compared with members of grazing food chains, was explained by their consumption of 13C‐enriched aphid honeydew.3. Myrmecophilous tree‐dwelling aphids were enriched in 13C and 15N relative to grass‐inhabiting species, and the honeydew of tree‐dwelling aphids had higher δ13C values than those of the honeydew of grass‐inhabiting aphids.4. The decrease in δ13C values of the worker ants from spring and summer to autumn apparently reflected the transition from the collection of tree sap and feeding on the aphid honeydew from trees with high 13C content in the spring and early summer to a more diverse liquid diet in late summer, which included 13C‐depleted honeydew of aphids from herbs.5. The prevalence of the 15N‐depleted aphid honeydew in the ants' diet in the second half of the summer is discussed as one possible explanation for the seasonal decline in δ15N values of the worker ants.

Grassland harvesting alters ant community trophic structure: An isotopic study in tallgrass prairies

“…This measure of TP is less sensitive to outliers and small sample sizes than conventional measures of trophic ranges (max TP − min TP,Jackson, Inger, Parnell, & Bearhop, 2011). While interand intra-annual fluctuations in ant and plant isotopic signatures might be problematic for using plants as basal resources(Iakovlev, Novgorodova, Tiunov, & Reznikova, 2017;Mooney & Tillberg, 2005), we did not detect significant differences in ant signatures across sample years and assume plant signatures were also consistent.Nevertheless, we interpret TP and TR as relative measures of trophic position and trophic range, respectively. Estimating actual TP and TR would require sampling the basal resources concurrently with ants.To determine how harvest influenced the trophic position and trophic range of ants, we used separate general linear models (GLM) with harvest treatment (control/harvest), ant species, and a harvest treatment × species interaction as fixed effects, and within-site averaged TP and TR values as the response variables.…”

Functional Role of Extrafloral Nectar in Boreal Forest Ecosystems under Climate Change

“…In mixed forests comprising conifers and deciduous broad-leaved birch in Europe and Asia, the red wood ant F. aquilonia is a dominant species. In spring the ants collect birch sap and nest-building materials, but predation on invertebrates is limited [78]. In sub-boreal deciduous forests of western Siberia, the F. aquilonia settlement capacity is lower than in boreal populations.…”

“…The amino acid content of EFN during flowering has not been studied, but an increase in amino acid content might make the ant distraction effect even stronger. In particular, ants require a high amino acid content when they are providing food for a queen [74], but nitrogen availability can be controlled by increasing the proportion of insect prey in their food [78].…”

“…However, according to both modern and fossil evidence, species at higher trophic levels, such as predators and parasitoids, are the most sensitive to climatic change [161]. Disruption of trophic interactions, e.g., through changes in plant phenology [120,161], range shift [48,49], or changes in atmospheric quality [18,159], can amplify climate change effects throughout the community and particularly on top-level predators of herbivores, such as ants in boreal forests [78].…”

“…Stable N and C isotope analyses have indicated that ant species with flexibility in their diet breadth have the greatest potential to be invasive or to adapt to changes in environment [78,162]. This means that the capacity to consume more carbon-based resources such as EFN and aphid honeydew and thus occupy a lower trophic level will improve the success of an ant species.…”