Oecologia (2008) 156:411–421 DOI 10.1007/s00442-008-0997-y 123 COMMUNITY ECOLOGY - ORIGINAL PAPER Ecological dominance of the red imported Wre ant, Solenopsis invicta, in its native range Luis A. Calcaterra · Juan. P. Livore · Alicia Delgado · Juan A. Briano Received: 6 October 2006 / Accepted: 1 February 2008 / Published online: 28 February 2008  Springer-Verlag 2008 Abstract Despite the widespread impacts invasive spe- cies can have in introduced populations, little is known about competitive mechanisms and dominance hierarchies between invaders and similar taxa in their native range. This study examines interactions between the red imported Wre ant, Solenopsis invicta, and other above-ground forag- ing ants in two habitats in northeastern Argentina. A com- bination of pitfall traps and baits was used to characterize the ant communities, their dominance relationships, and to evaluate the eVect of phorid Xies on the interactions. Twenty-eight ant species coexisted with S. invicta in a gal- lery forest gap, whereas only ten coexisted with S. invicta in a xerophytic forest grassland. S. invicta was the most numerically dominant species in the richest and complex habitat (gallery forest); however it performed better as dis- coverer and dominator in the simpler habitat. S. invicta was active during day and night. In spite of its poor capacity to discover resources, S. invicta showed the highest ecological dominance and the second-best behavioral dominance after Camponotus blandus. S. invicta won 78% of the interac- tions with other ants, mostly against its most frequent com- petitor, Pheidole cf. obscurithorax, dominating baits via mass recruitment and chemical aggression. P. cf. obscuri- thorax was the best food discoverer. S. invicta won 80% of the scarce interactions with Linepithema humile. Crema- togaster quadriformis was one of the fastest foragers and the only ant that won an equal number of contests against S. invicta. The low presence of phorid Xies aVected the for- aging rate of S. invicta, but not the outcome of interspeciWc interactions. This study revealed that the red imported Wre ant ecologically dominated other terrestrial ants in its native range; however, other species were able to be numerically dominant or co-dominant in its presence. Keywords Competitive mechanisms · Dominance hierarchies · Ant assemblages · Phorid Xies · Biological invasion Introduction Introductions of exotic ant species are responsible for declines in the number and abundance of native ant species and other arthropods (Vitousek et al. 1996; Porter and Savignano 1990; Holway 1998). However, few studies focus on invasive species in their native range to under- stand the causes of a successful invasion (Ross et al. 1996; Porter et al. 1997; Orr and Seike 1998; Tsutsui et al. 2000; Callaway and Aschehoug 2000; LeBrun et al. 2007). In par- ticular, little is known about mechanisms promoting eco- logical co-existence between invaders and similar taxa in their native land. One of the factors governing the community structure of ants is the interspeciWc competition for resources via exploitative and interference mechanisms (Wilson 1971; Fellers 1987; Hölldobler and Wilson 1990; Davidson 1998; Communicated by Craig Osenberg. L. A. Calcaterra (&) · J. A. Briano USDA-ARS-South American Biological Control Laboratory, Bolivar 1559 (B1686EFA), Hurlingham, Buenos Aires, Argentina e-mail: trapisonda@tutopia.com; luiscalcaterra@hotmail.com Juan. P. Livore Southern Seas Ecology Laboratories, Darling Building DP 418, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA 5005, Australia A. Delgado The Conservation Land Trust Argentina, Carlos Pellegrini 1140 (3400), Corrientes, Argentina