An Experimental Study of Competition Between Fire Ants and Argentine Ants in Their Native Range

Abstract

An understanding of why introduced species achieve ecological success in novel environments often requires information about the factors that limit the abundance of these taxa in their native ranges. Although numerous recent studies have evaluated the importance of natural enemies in this context, relatively few have examined how ecological success may result from differences in the magnitude of interference competition between communities in the native and introduced ranges of nonnative species. Here we examine how native-range competitive environments may relate to invasion success for two important invasive species, the red imported fire ant (Solenopsis invicta) and the Argentine ant (Linepithema humile), in a region of native-range sympatry. At two study sites in northern Argentina, we used stable-isotope analysis, a variety of observational approaches, and two different reciprocal removal experiments to test (1) whether S. invicta competes asymmetrically with L. humile (as suggested by the 20th century pattern of replacement in the southeastern United States) and (2) the extent to which these two species achieve behavioral and numerical dominance. Stable-isotope analysis and activity surveys indicated that S. invicta and L. humile are both omnivores and forage during broadly overlapping portions of the diel cycle. Short-term removal experiments at baits revealed no competitive asymmetry between S. invicta and L. humile. Longer-term colony removal experiments illustrated that S. invicta and L. humile experience an approximately equal competitive release upon removal of the other. Our results indicate that neither S. invicta nor L. humile achieves the same degree of behavioral or ecological dominance where they co-occur in native populations as they do in areas where either is common in their introduced range. These results strongly suggest that interspecific competition is an important limiting factor for both S. invicta and L. humile in South America.

Intercontinental differences in resource use reveal the importance of mutualisms in fire ant invasions

“…2 and Table S2). Hence, our results support the hypothesis that interspecific competition prevents S. invicta from monopolizing mutualist-provided carbohydrates in its native range, whereas a lack of strong competitors in the United States allows S. invicta greater access to these critical resources (20,21).…”

“…Hence, monopolization of honeydew and other carbohydrate-rich resources seems likely to contribute to the success of S. invicta invasions (15). However, next to nothing is known about resource use of S. invicta in native populations in South America, which on average are less dense (20) and experience greater interspecific competition (20,21) than introduced populations. In this study we combined field surveys, manipulative experiments, and stable isotope analyses to quantify (i) the degree to which introduced populations of S. invicta have access to mutualisms and their associated high-carbohydrate resources, compared with the degree of access experienced by native populations, and (ii) how access to mutualist-provided carbohydrates contributes to colony performance under both field and laboratory conditions.…”

Trophic ecology of invasive Argentine ants in their native and introduced ranges

“…27). The extensive overlap in ␦ 15 N values between L. humile and other ants suggests that competition for animal-based protein is fierce, a contention supported by LeBrun et al (28).…”

“…Sites in Argentina include three woodland/pasture locations along the Parana and Paraguay Rivers: (i) Reserva Natural Otamendi, Buenos Aires Province (34°13Ј30Љ S, 58°54Ј00Љ W), (ii) 6 km E Villa Ocampo, Santa Fe Province (28°30Ј30Љ S, 59°16Ј20Љ W), and (iii) 5 km E Herradura, Formosa Province (26°31Ј05Љ S, 58°16Ј50Љ W). Previous research at these sites (referred to as Otamendi, Ocampo, and Herradura) demonstrates that Argentine ants coexist with a diverse assemblage of native ants (28,44). Sites in California include three scrub sites in San Diego County, California: (i) Otay-Sweetwater Unit of the San Diego National Wildlife Refuge (32°43Ј45Љ N, 116°56Ј30Љ W), (ii) University of California Elliot Chaparral Reserve (32°53Ј30Љ N, 117°06Ј10Љ W), and (iii) Torrey Pines State Reserve Extension (32°56Ј25Љ N, 117°14Ј55Љ W).…”

Convergent evolution of levee building behavior among distantly related ant species in a floodplain ant assemblage

“…Despite the frequency of this natural disturbance regime, the ground-nesting ants in this region of South America are impressively abundant and diverse (see LeBrun et al, 2007;Tillberg et al, 2007). Following the first local rains in over a month, we observed five distantly related species in this habitat constructing earthen walls immediately adjacent to the lips of their nest entrances: Pheidole cf.…”