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

Abstract

Trophobiosis between aphids (Aphididae, Hemiptera) and ants (Formicidae, Hymenoptera) is considered to provide an important source of nutrition for ants by aphid honeydew and aphids themselves used as prey. However, little is known about nutrient fluxes and the relative importance of trophobiosis for different ant species. Combining direct contact observations between ants and aphids with stable isotope analyses of distinct multitrophic sample sets (soil, plant, aphid, and ant), we aimed at disentangling the importance of trophobiosis in a Mediterranean food web and possible feedbacks on the functional diversity of ants in a species-rich organic Citrus plantation. We analyzed d 13 C-and d 15 N-values of sample sets for fertilized and natural soil, using the fertilizer as natural isotope label. The results showed trophic relationships between 18 host plant species, 22 aphid species, and 7 ant species. Direct observation revealed at least 40 different plant-aphid combinations and 25 aphid-ant combinations with a marked range of d 15 N-values. However, the d 13 C and d 15 N isotope ratios still reflected the trophic levels. A significant correlation occurred between the isotope ratios of aphids and their host plants. However, no relationship was found between aphids and ants or between plants and ants revealing that many ant species do not exhibit a close relationship with their trophobiotic partners. Isotopic data allowed us to separate ant species into trophic functional groups and showed the relevance of other food resources. The applied fertilizer shifted the isotopic baseline for the whole trophic system. By combining the stable isotope analysis with the exact origin of the samples, we avoided a misleading interpretation of the high isotopic range of species. Thus, we emphasize the importance of considering a baseline in stable isotope food web studies.

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

“…, Brewitt et al. , Parmentier et al. ), although this does not explain the similar δ 15 N values between treatments.…”

How plants and honeydew-producing hemipterans affect ant species richness and structure in a tropical forest zone

“…Whether through numeric dominance or shelter, honeydew monopolization is a factor that limits competition within the ant assemblage and reduces co-occurrence on the source. Ant-hemipteran associations are known to provide mutual benefit (Buckley and Gullan 1991;Del-Claro and Oliveira 2000) although some studies had not confirmed this view (Zachariades et al 2009;Brewitt et al 2015). The potential benefit to the plant, which can be protected by the predatory behavior of the ant against herbivores is not always clear and can be controversial (Mody and Linsenmair 2004;Ness and Bronstein 2004).…”

“…There is considerable variation in EFN morphology and visitor spectra of ants among other insects (Oliveira and Brandão 1991;Brewitt et al 2015). Associations of ants and hemipterans, on the other hand, occur in many if not on all flowering plant families and are widespread from tropical to temperate habitats (Way 1963;Buckley 1987).…”

Application of CO2 carbon stable isotope analysis to ant trophic ecology

“…Applications in studies of insects include the determination of resource origin (Ouyang et al, 2015), movements (Madeira et al, 2013, 2014; Zhang et al, 2020), and feeding periods (Ouyang et al, 2014), as well as the study of nutrient uptake (Pollier et al, 2016) and allocation (Levin et al, 2017a,b). In ant ecology, SIA is used to study the trophic role of each species (e.g., Ottonetti et al, 2008), to infer how ant assemblages vary in different habitat conditions (Gibb & Cunningham, 2011), to estimate the importance of trophobiosis (Brewitt et al, 2015), and to study the effects of natural local baseline variations (Cronin et al, 2015) and colony parameters (Barriga et al, 2013) on isotopic signatures. This approach requires destructive sampling and is therefore difficult to use when dealing with rare species or when repeated measurements on the same subjects are desired (Hatch et al, 2002b).…”

“…Still, different food preferences can be found in different taxa. For example, Formicinae generally tend to feed on lower trophic levels (mainly homopteran honeydew or plant extrafloral nectaries) compared to Myrmicinae, which are more carnivorous, although generalizations are problematic (Fiedler et al, 2007; Blüthgen & Feldhaar, 2010; Brewitt et al, 2015). Food selection is determined by several other factors such as resource distribution and availability, food quality and quantity, handling time, and colony nutritional requirements (Csata & Dussutour, 2019).…”