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

Abstract

Mutualisms play key roles in the functioning of ecosystems. However, reciprocally beneficial interactions that involve introduced species also can enhance invasion success and in doing so compromise ecosystem integrity. For example, the growth and competitive ability of introduced plant species can increase when fungal or microbial associates provide limiting nutrients. Mutualisms also may aid animal invasions, but how such systems may promote invasion success has received relatively little attention. Here we examine how access to food-for-protection mutualisms involving the red imported fire ant ( Solenopsis invicta ) aids the success of this prominent invader. Intense interspecific competition in its native Argentina constrained the ability of S. invicta to benefit from honeydew-producing Hemiptera (and other accessible sources of carbohydrates), whereas S. invicta dominated these resources in its introduced range in the United States. Consistent with this strong pattern, nitrogen isotopic data revealed that fire ants from populations in the United States occupy a lower trophic position than fire ants from Argentina. Laboratory and field experiments demonstrated that honeydew elevated colony growth, a crucial determinant of competitive performance, even when insect prey were not limiting. Carbohydrates, obtained largely through mutualistic partnerships with other organisms, thus represent critical resources that may aid the success of this widespread invasive species. These results illustrate the potential for mutualistic interactions to play a fundamental role in the establishment and spread of animal invasions.

Ant nutritional ecology: linking the nutritional niche plasticity on individual and colony-level to community ecology

“…When colonies of the Argentine ant Linepithema humile as well as the fire ant S. invicta are still small and newly established they feed on a more protein-biased diet (mostly prey) while larger colonies were able to monopolize trophobionts and feed on a carbohydrate-biased diet. This dietary shift results in much higher colony growth rates in both species -and thus larger community-level effects -when fed a carbohydrate-biased diet [35][36][37].…”

Mechanisms of Competitive Displacement of Native Ant Fauna by Invading <I>Myrmica rubra</I> (Hymenoptera: Formicidae) Populations

“…Invading foragers may also have an energetic advantage at high densities given an apparent surplus of carbohydrates from homopteran sources relative to the availability of protein (Davidson 1998, Helms and Vinson 2008, Wilder et al 2011, Shik and Silverman 2012. Despite the importance of invasive ant species on biodiversity and ecosystem function on a global scale, the mechanisms driving displacement of native fauna have only been studied in a handful of species (Kenis et al 2009).…”

Stable nitrogen and carbon isotope ratios in wild native honeybees: the influence of land use and climate

“…Stable nitrogen isotopes have been used to indicate food resource partitioning and changes in food web structures among insect populations and communities in relation to environmental changes. For example, stable nitrogen analyses revealed 15 N enrichments of non-native ants tend to be lower in non-native environments than in native environments (Tillberg et al 2007;Wilder et al 2011). Stable nitrogen ratios have also shown land use alterations result in modifications in feeding habitats of ants as a result of the prey availability (Gibb and Cunningham 2011;Woodcock et al 2013).…”