Behavioral responses to numerical differences when two invasive ants meet: the case of Lasius neglectus and Linepithema humile

Abstract

Two of the world’s most invasive ants, Linepithema humile and Lasius neglectus, are destined to overlap in range as they continue to spread throughout Europe. Although L. humile arrived first, and is therefore more numerically abundant, L. neglectus is the more behaviorally dominant of the two. We performed lab trials to determine whether L. humile could use numerical abundance to overcome the behavioral dominance of L. neglectus and whether the ants’ behavioral patterns shifted when the species co-occurred. We found that L. neglectus was more aggressive when less abundant, whereas the opposite was true of L. humile. When L. neglectus was outnumbered, it employed aggressive behaviors, such as biting or chemical attacks, more frequently than L. humile; it also utilized a behavioral sequence that included mandible opening and biting. Our results for these species support the hypothesis that species modulate their behavior towards competitors, which facilitates the understanding of how multiple invasive ant species can co-occur in a given area. Moreover, our study shows that the co-occurrence of invasive species could result from the use of two strategies: (1) the Bourgeois strategy, in which aggressiveness changes based on numerical dominance and (2) the dear-enemy strategy, in which aggressiveness is reduced when competitors co-occur. Since these strategies may lead to territory partitioning, we suggest that the behavioral flexibility displayed by both species when they overlap may allow local co-occurrence and increase their likelihood of co-occurrence during their range expansion in Europe, which could have a negative cumulative impact on invaded areas.

Local coexistence of native and invasive ant species is associated with micro-spatial shifts in foraging activity

“…niger colonies maintained their pre-invasion spatial distribution but changed their foraging strategy to better avoid or outcompete T. magnum (e.g., changes in the foraging distance or number of foragers recruited). Phenotypic plasticity in thermal tolerance, competitive behaviour or diet (Bujan et al 2020;Balzani et al 2021;Trigos-Peral et al 2021) might help species co-exist locally, for example by limiting direct competitive interactions. Future research could explore if it enables L. niger to persist in invaded areas.…”

A systematic examination of learning in the invasive antLinepithema humilereveals very rapid development of short and long-term memory

“…The Argentine ant ( Linepithema humile (Mayr, 1868)) is one of the most damaging ant species worldwide, and the most widespread invasive ant in Europe (Human and Gordon 1999; Trigos-Peral et al 2021; Angulo et al 2022). The presence of L. humile in invaded areas causes a massive decrease in invertebrate diversity and even affects vertebrates (Wetterer et al 2001; Suarez et al 2005; Alvarez-Blanco et al 2021).…”

The Native Ant Lasius niger Can Limit the Access to Resources of the Invasive Argentine Ant

“…Moreover, the bourgeois strategy could be a mechanism used by L. humile to co-occur with La. neglectus [ 49 ]. In this sense, because of the recent expansion of La.…”