Trophic ecology of the invasive argentine ant: spatio-temporal variation in resource assimilation and isotopic enrichment

Abstract

Studies of food webs often employ stable isotopic approaches to infer trophic position and interaction strength without consideration of spatio-temporal variation in resource assimilation by constituent species. Using results from laboratory diet manipulations and monthly sampling of field populations, we illustrate how nitrogen isotopes may be used to quantify spatio-temporal variation in resource assimilation in ants. First, we determined nitrogen enrichment using a controlled laboratory experiment with the invasive Argentine ant (Linepithema humile). After 12 weeks, worker δ15N values from colonies fed an animal-based diet had δ15N values that were 5.51% greater compared to colonies fed a plant-based diet. The shift in δ15N values in response to the experimental diet occurred within 10 weeks. We next reared Argentine ant colonies with or without access to honeydew-producing aphids and found that after 8 weeks workers from colonies without access to aphids had δ15N values that were 6.31% larger compared to colonies with access to honeydew. Second, we sampled field populations over a 1-year period to quantify spatio-temporal variability in isotopic ratios of L. humile and those of a common native ant (Solenopsis xyloni). Samples from free-living colonies revealed that fluctuations in δ15N were 1.6–2.4‰ for L. humile and 1.8–2.9‰ for S. xyloni. Variation was also detected among L. humile castes: time averaged means of δ15N varied from 1.2 to 2.5‰ depending on the site, with δ15N values for queens ≥ workers > brood. The estimated trophic positions of L. humile and S. xyloni were similar within a site; however, trophic position for each species differed significantly at larger spatial scales. While stable isotopes are clearly useful for examining the trophic ecology of arthropod communities, our results suggest that caution is warranted when making ecological interpretations when stable isotope collections come from single time periods or life stages.

Ecological effects of multi‐species, ant–hemipteran mutualisms in citrus

“…5). Given that the Argentine ant forms populous and expansive colonies that depend on carbohydrates for colony growth (Grover et al, 2007;Kay et al, 2010;Menke et al, 2010), it seems unlikely that HPH taxa compete for tending services in this system. Positive indirect effects among HPH taxa that result from ant tending might thus be expected in other situations where ants form large colonies and exhibit dietary preferences for carbohydrates.…”

“…Here we investigate the ecological effects of multi-species mutualisms involving the Argentine ant [Linepithema humile (Mayr)] and five species of honeydew-producing hemipterans (HPHs) in a citrus agroecosystem. The Argentine ant often tends HPHs for their honeydew (Way, 1963), and this resource is important for colony growth (Menke et al, 2010), as are carbohydrates more generally (Grover et al, 2007;Kay et al, 2010). Multi-species mutualisms involving ants and HPHs are pervasive in citrus, even at fine spatial scales (e.g.…”

Ant–plant mutualism: a dietary by‐product of a tropical ant's macronutrient requirements

“…It is possible that the season when the ants were collected or the specific location of the experimental plots drastically changed the isotopic values, as it has been demonstrated in other studies (e.g., Menke et al. ). This enrichment however does not invalidate the observed differences in isotope ratios between the experimental treatments.…”

Riverine Landscape Patches Influence Trophic Dynamics of Riparian Ants

“…ground beetles; Hering and Plachter, ), and may represent an important nutritional subsidy for ants in our study at discrete time periods given the pulsed nature of aquatic insect emergence (Baxter et al ., ; Hoekman et al ., ). We also found no relationship between δ 13 C values of ants and terrestrial vegetation (Figure ), which may suggest that ants in this system mostly subsist on terrestrial seeds or terrestrial honeydew (via aphid excretions), which were not sampled but typically have higher carbon isotope ratios than those of cellulose or lignin owing to the soluble sugar or carbohydrate content (Menke et al ., ; Gibb and Cunningham, ). In the same study system, Tagwireyi and Sullivan () found differences in ant assemblage composition among riverine landscape patch types (where F. subsericea was one of three numerically dominant species), largely citing both structural (e.g.…”