Stable N-isotope signatures of central European ants – assessing positions in a trophic gradient

Abstract

Studies employing stable isotope technology have greatly contributed to understanding trophic relationships of tropical ants, but temperate-zone ants remain under-explored. We studied d 15 N values of 43 ant species from three subfamilies sampled across central Europe. After statistically accounting for the effects of elevation and geographical location of habitats, which alter the isotopic composition of nitrogen in ecosystems, significant patterns in N-isotope signatures were detected. These signatures hint at differences across ants in the contribution of plant-derived nitrogen obtained via trophobiosis and nectarivory relative to nitrogen obtained via predation and scavenging. In general, Myrmicinae had higher d 15 N values than Formicinae, in line with a greater relative importance of trophobiosis in the latter. The genus Myrmica scored especially high, indicating predominantly predacious nitrogen sources. Remarkably, also the granivore Messor cf. structor had high d 15 N values. This suggests that, despite the major portion of food uptake being made up by plant seeds, this ant could derive substantial fractions of its nitrogen budget from feeding on arthropod corpses or vertebrate faeces. Moreover, this highlights that deductions from observed quantities of ingested food on its relative contribution to ants matter balance should be accompanied by isotope analyses. At the other end of the spectrum, Camponotus and Plagiolepis had low d 15 N values. In line with multiple field observations, this suggests a contribution of trophobiosis not only to their energy, but also to their nitrogen budget. Formica and Lasius had intermediate 15 N values, which is in agreement with the current view that these ants have mixed diets with a balance between trophobiosis and predation. A possible influence of endosymbiotic bacteria on the isotope signatures of several genera is discussed. This study provides a first application of stable isotope technology to estimate the role of plant-derived nutrients to the nitrogen budget of a larger range of central European ants. Furthermore, it shows that Nisotope analysis is applicable across extended ecological and geographical gradients. Future studies along this line are promising to complement our current understanding of the nutritional ecology of temperate-zone ants.

Evaluating the importance of trophobiosis in a Mediterranean ant community: a stable isotope analysis

“…Mean d 15 N-values of workers of most abundant species and Table 1 genera in Central Europe typically span a range of approx. 3 % in diverse dry grasslands (Sanders and Platner, 2007;Ó Grady et al, 2010) and other habitats (Fiedler et al, 2007). Similarly, in the dry grasslands mean d 13 C-values of workers also span a relatively small range of approx.…”

“…If trophic enrichment between tissues, species, and trophic levels is constant, a regression line between two components of sample sets is expected to have a slope of 1.0 and an intercept equal to the degree of fractionation. Fiedler et al (2007) studied 43 ant species in the European temperate zone and gained detailed insight into isotopic patterns of central European ants showing that trophobiosis is in fact an important form of nutrition for the ant genera Formica, Lasius, Camponotus, and Plagiolepis. Ottonetti et al (2008) successfully identified the food web position (d 15 N signal) and carbon sources (d 13 C signal) from lower level (like Homopteran tending) to high level (with predation) of five ant species in Italy.…”

Resource discovery in ant communities: do food type and quantity matter?

“…In temperate ant communities, the majority of species are omnivores, competing for the same resource pool of insect and plant matter (Vepsäläinen & Pisarski, 1982;Fellers, 1987;Hölldobler & Wilson, 1990;Retana & Cerdá, 1994;Morrison, 1996;Holway, 1999;Fiedler et al, 2007). They are also, with few exceptions, central-place foragers (Hölldobler & Wilson, 1990) that specialise on different components of foraging success, trading off between discovery (resource encounter) and dominance (resource harvest and control) abilities (Vepsäläinen & Pisarski, 1982;Fellers, 1987;Morrison, 1996;Davidson, 1998;Holway, 1999;.…”

Trophobiosis in the arboricolous ant Liometopum microcephalum (Hymenoptera: Formicidae: Dolichoderinae)

“…Velasco Corona et al (2007) report that Liometopum appiculatum in Tlaxcala, Mexico, has a trophobiotic relationship with 14 species of Sternorrhyncha. The particularly high  15 N reported in L. microcephalum (albeit based on a sample from a single colony) compared to other ant species would indeed indicate a predominance of zoophagy in this species (Fiedler et al, 2007). However, contrary to the preceding claims of strict zoophagy in L. microcephalum, Wiest (1967) reports from a site in Austria that the trails of L. microcephalum also lead to bark aphids of the genus Stomaphis.…”