Insectes Sociaux (2020) 67:179–187 https://doi.org/10.1007/s00040-020-00750-z Insectes Sociaux RESEARCH ARTICLE Disentangling resource acquisition from interspecifc behavioral aggression to understand the ecological dominance of a common, widespread temperate forest ant R. J. Warren II1 · J. R. King2 · M. A. Bradford3 Received: 29 August 2019 / Revised: 30 November 2019 / Accepted: 11 January 2020 / Published online: 24 January 2020 © International Union for the Study of Social Insects (IUSSI) 2020 Abstract Ant communities are structured, in part, by competition between related and unrelated ant species for territories and food resources. In eastern deciduous forests of the United States, a single ant genus (Aphaenogaster) appears ecologically dominant with high abundance and opportunistic foraging. However, Aphaenogaster ants are not particularly behaviorally aggressive toward co-occurring ants, making it unclear as to how they might sustain dominance. We ofered myrmecochorous seeds and termite carrion at bait stations and quantifed ant aggression, food selection and recruitment. We conducted the experiments throughout the natural seed-release window to determine how the abundance of low- and high-quality food items impacted behavior. We found evidence that Aphaenogaster ants dominate the retrieval of both seeds and insect carrion (dead termites). Aphaenogaster foraging dominance did not appear driven by superior fghting or recruitment abilities but simply by having more foragers on the ground, essentially achieving control of diferent types of food resources through numerical dominance. Moreover, though they are the dominant efective seed dispersers in the system, A. picea exhibited a much greater afnity for termites than seeds, and the desirability of termites decreased in the presence of seeds. Overall, our results suggest that high numbers of foragers—as opposed to aggressive territoriality—can be an efective ecological strategy for sustaining ecological dominance through resource acquisition. Keywords Aphaenogaster · Dispersal · Myrmecochores · Species interactions Introduction and formic acid attacks, and foraging workers also can be seen securing resources through stealing, fast discovery and Ant ecology is anchored in understanding interspecifc com- retrieval, or simply overwhelming resources with recruited petition (Adams 2016; Cerda et al. 2013; Hölldobler and co-workers. In some cases, these behaviors may shape ant Wilson 1990; Parr and Gibb 2009). Fighting workers can communities through interspecifc territoriality, but ant pop- be observed in aggressive behaviors such as biting, stinging ulations also are self-limiting which suggests a substantial role for intraspecifc competition (Adams 2016; Gibb and Johansson 2011; Parr and Gibb 2009). Moreover, colony * R. J. Warren II establishment, such as queen dispersal patterns, is increas- [email protected] ingly recognized as important in shaping ant community J. R. King structure (Andersen 2008; King and Tschinkel 2016). [email protected] Interspecifc behavioral dominance hierarchies are used M. A. Bradford to explain patterns of ant species co-existence and, in com- [email protected] bination with numerical dominance, to explain ecological 1 Department of Biology, SUNY Bufalo State, 1300 dominance (the ecological impact of a species) among co- Elmwood Avenue, Bufalo, NY 14222, USA occurring species (Hölldobler and Wilson 1990). Given that 2 Biology Department, University of Central Florida, 4110 ants exhibit direct (e.g., aggression) and indirect competition Libra Drive, Orlando, FL 32816, USA (e.g., foraging efectiveness), a simplifying assumption is 3 School of Forestry and Environmental Studies, Yale that greater ability in one axis corresponds with decreased University, New Haven, CT 06511, USA ability in the other (“Dominance-discovery trade-off”, Vol.:(0123456789)1 3 180 R. J. Warren II et al. Fellers 1987). However, empirical evidence suggests that a key nutrients for ants (Fischer et al. 2008; Gammans et al. clear trade-of in these abilities is not ubiquitous in ant spe- 2005; Lanza et al. 1992) so that their retrieval and consump- cies and many species, particularly non-native ants, excel tion may supplement ant diets (Clark and King 2012; Gam- in both dominance and discovery (Adler et al. 2007; Parr mans et al. 2005), but Aphaenogaster ants occur and thrive and Gibb 2011). Stuble et al. (2017) suggest that the use of in the absence of myrmecochorous plants (Mitchell et al. behavioral hierarchies, specifcally dominance hierarchies, 2002; Warren II et al. 2019) whereas they depend on inver- as a proxy for ecological dominance is spurious as behav- tebrate carrion (Buczkowski and Bennett 2007; Lubertazzi ioral hierarchies efectively ignore resource acquisition and 2012). Whereas Aphaenogaster ants typically monopolize cannot quantitatively assess diferences in resource acquisi- seed retrieval in eastern North American forests (Lubertazzi tion, colony abundance, or forager abundance. We focus on 2012; Ness et al. 2009), their efectiveness in scavenging understanding the ability of species to occupy and gather other food items is not as well studied. resources as a determinant of ecological dominance, and Our objective was to determine whether Aphaeno- behavioral interactions at bait stations act as a descriptor that gaster ants are dominant in acquiring seeds and carrion, matters if aggressive behaviors afect resource acquisition. and if such dominance is behavioral (e.g., aggression) or Aphaenogaster species in eastern North American decid- ecological (e.g., resource discovery). We expected, given uous forests are overwhelmingly the most abundant ant on the higher food quality and desirability of termite carrion the forest foors (King et al. 2013; Lubertazzi 2012); yet, (Buczkowski and Bennett 2008; Warren II et al. 2015a), that despite their numbers, when confronted with more aggres- Aphaenogaster ant aggression would be higher at termite- sive ant species, Aphaenogaster ants generally are displaced bait stations. Alternately, Aphaenogaster ant dominance for from bait stations and nest sites (Lubertazzi 2012; Stuble either food item might just refect forager density. We also et al. 2012; Warren II et al. 2012, 2015a). Hence, Aphae- examined whether mixing seeds and termites infuenced nogaster food retrieval success (discovering and retriev- retrieval; given that termites are a preferred food item for ing food) may be due to numerical abundance rather than ants, we predicted that seed removal would be higher when aggression/retrieval dominance. Another possibility is that mixed with termites. Alternately, if seeds are a poorer food foraging workers mass recruit additional foragers from the choice, their presence may diminish termite removal at colony using pheromone trails to the food resource (Bona- mixed bait stations. Given that there is some indication that beau et al. 1998; Hölldobler and Wilson 1990), although there may be seasonality in ant preference for seeds, most Aphaenogaster species are not generally considered efective notably that ants may prefer seeds in early spring when other recruiters (Lubertazzi 2012). As such, Aphaenogaster’s rela- food sources are less available (Carroll and Janzen 1973), tive dominance in the forest foor is likely a function of rapid we examined seed and termite carrion retrieval through the discovery and retrieval of food items, potentially facilitated spring and early summer season. by the high density of foragers, so that they follow the classic dominance-discovery trade-of as subordinate ants adept at quickly fnding and retrieving food (Fellers 1987; Lubertazzi Methods 2012; Stuble et al. 2012). Aphaenogaster ants are the key elaiosome-bearing Study species and site descriptions myrmecochorous plant (ant-dispersed) disperser in east- ern deciduous forests, generally retrieving ~ 75% of seeds Aphaenogaster congeners are the most common ants in ofered at bait stations and efectively dispersing them (Ness understory habitats in eastern North American (N.A.) for- et al. 2009; Warren II and Giladi 2014; Warren II et al. ests (King et al. 2013; Lubertazzi 2012), and they are the 2010, 2014). Ant-mediated seed dispersal is a cosmopoli- main dispersers of myrmecochorous seeds in these habi- tan species interaction (sensu stricto) in which a chemically tats (ca. 75% of those removed, Ness et al. 2009; Warren attractive seed appendage (elaiosome) prompts dispersal by II et al. 2010, 2014). Aphaenogaster ants generally forage omnivorous foraging ants (e.g., Beattie and Hughes 2002; individually 60–120 cm away from their nests, although Gorb and Gorb 2003; Rico-Gray and Oliveira 2007). Seed they are capable of weak recruitment of a small number attractiveness for the ants generally increases with elaiosome of nestmates (typically less than ten workers) to large food size (Bas et al. 2009; Garrido et al. 2002; Gorb and Gorb resources (Lubertazzi 2012). Nests are usually located under 1995; Hughes and Westoby 1992; Warren II et al. 2014). or in logs and under rocks, though sometimes small nests Resource acquisition may be afected by food type. Aphaeno- may be found in a twig or folded leaf (King et al. 2013; gaster ants are generalist scavengers with diets ranging from Lubertazzi 2012). In our study area, the local Aphaeno- invertebrates to fungi to seed elaiosomes, but invertebrates gaster species is A. picea (Wheeler 1908). Specifcally, our appear to make up a majority of their diet (Buczkowski and study took