A year in an ant's life: Opportunism and seasonal variation in the foraging ecology ofAphaenogaster senilis

Abstract

Ants are important consumers in most terrestrial ecosystems. They show a great diversity of diets and foraging strategies. Here, we analyzed how circannual variation in resource use by the Mediterranean species Aphaenogaster senilis is related to colony life cycle and resource availability. In southwestern Spain, this species is active almost yearround, but foraging intensity decreases 10fold between March and November, following larval production. In the summer, ants refrain from foraging at midday to avoid high temperatures. We hypothesized that diet and foraging plasticity could also explain the ecological success of this species. There are several techniques for assessing the diet of ants. Combining isotope analyses with conventional methods can provide better taxonomic resolution of resource utilization. Using a combination of classic and isotopic analyses, we found that 1) the proportion of plant and animalderived items collected by foragers did not vary significantly from March to November, and 2) isotope analyses indicated a decrease in the trophic level of A. senilis between June and September, suggesting a difference between collected material and items assimilated. Interestingly, most animal prey were collected by individual ants, and many were retrieved alive. Therefore, A. senilis is not only a scavenger, but also a nonnegligible predator, particularly of aphids. The abundance of the most common animalderived items in the diet was proportional to their abundance in the study area. We conclude that A. senilis is an opportunistic species that is able to feed on a variety of resources, which may be key to its ecological success.Résumé : Les fourmis sont des consommateurs importants dans la plupart des écosystèmes terrestres. Elles montrent une grande diversité de stratégies de recherche de nourriture et de régimes alimentaires. Nous avons analysé comment la variation circannuelle de l'utilisation des ressources par l'espèce méditerranéenne Aphaenogaster senilis est reliée au cycle de vie de la colonie et à la disponibilité des ressources. Au sudouest de l'Espagne, cette espèce est active presque toute l'année, mais l'intensité de sa quête alimentaire est réduite d'un facteur 10 entre mars et novembre après la production de larves. En été, les fourmis s'abstiennent de fourrager au milieu de la journée pour éviter les températures trop élevées. Nous avons formulé l'hypothèse que la plasticité du régime et de la quête alimentaires pourrait aussi expliquer le succès écologique de cette espèce. Il y a plusieurs techniques pour déterminer le régime alimentaire des fourmis; la combinaison d'analyses isotopiques et de méthodes classiques peut fournir une meilleure résolution taxonomique de l'utilisation des ressources. En combinant des analyses classiques et isotopiques, nous avons trouvé : 1) que la proportion de plantes et d'éléments d'origine animale récoltés par les fourmis fourrageuses ne variait pas significativement entre mars et novembre; et 2) les analyses isotopiques ont indiqué une diminution du nive...

The effects of fire on ant trophic assemblage and sex allocation

“…However, they did observe that different plant items were collected depending on their availability. Indeed, the complementary use of traditional observations and isotopic dietary analysis in ants has confirmed that nitrogen isotopic values shift when there is a small modification in the diet (Caut et al 2013a). In our study, fire had no effect on overall ant isotopic values across time; no difference was observed between values obtained 1 month and 1 year after fire.…”

“…In addition, food may be unevenly distributed among colony members (queens, workers, larvae [LI], etc.). Thus, stable isotope analysis provides a powerful alternative approach in such circumstances (Kelly 2000;Caut et al 2009Caut et al , 2013a. This method is based on the notion that an organism's nitrogen and carbon isotopic ratios (d 13 C and d 15 N) provide a record of the resources it has assimilated (see Post 2002;for review).…”

Dispersal of non-myrmecochorous plants by a “keystone disperser” ant in a Mediterranean habitat reveals asymmetric interdependence

“…Primary dispersal allowed transporting most A. italicum fruits an average of 2-4 m away from the mother plant. This corresponds to the average foraging distance of A. senilis (Cerdá et al, 2009). This dispersal distance may be sufficient to promote the colonization of new habitats for small herbs like A. italicum but might not be relevant for shrubs whose fruits can be transported a 100 m by birds (Traveset, 1994;Hulme, 1997).…”

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“…had a quick response on day on the first day that disappeared on the second day. Aphaenogaster senilis Mayr is an opportunistic species that is able to adjust its diet according to the resources of the area (Caut et al, ). This characteristic may help exploit dynamic resources and may explain the higher number of captures in the first few hours after setting the traps when environmental disturbances are most fresh.…”