Competitive Mechanisms Underlying the Displacement of Native Ants by the Invasive Argentine Ant

Abstract

The Argentine ant (Linepithema humile) is a widespread invasive species that competitively displaces native ants throughout its introduced range. Although this pattern of displacement is well known, its underlying mechanisms remain little studied. To gain a more detailed understanding of this widespread competitive displacement, I compared the exploitative and interference abilities of the Argentine ant with those of seven species of native ants it displaces in riparian woodlands in northern California. I performed four different manipulative field experiments; each measured different aspects of the competitive ability of the eight species of ants in this study. The main goals of this study were to identify the mechanisms responsible for the Argentine ant's strong competitive ability, to determine if native ants are subject to species-specific trade-offs in exploitative and interference ability typically present among coexisting ants, and if so, to assess whether Argentine ants are subject to this trade-off as well.Argentine ants located and recruited to baits as quickly or more quickly than did native ants-both in areas where Argentine ants and native ants occurred together (i.e., at the edge of invasion fronts) and where they occurred separately (i.e., away from invasion fronts). Along the edge of invasion fronts, Argentine ants also controlled a greater proportion of baits than did native ants. In one-on-one interactions, individual Argentine ant workers experienced mixed success in overcoming individual workers of the seven native ant species. When fighting against native ants, Argentine ants used both physical aggression and chemical defensive compounds, although the latter mechanism was more often successful in deterring opponents. Chemical defensive compounds produced by Argentine ants were repellent but appeared no more so than those of native ants. Although Argentine ant workers were not able to overcome native ant workers consistently, Argentine ant colonies succeeded in displacing most native ant colonies from baits. The discrepancy between worker-level and colony-level interference ability suggests that numerical advantages are key to the Argentine ant's proficiency at interference competition.Like ants in other communities, the native ants in this study were subject to a competitive trade-off in which interference ability and exploitative ability were negatively correlated. In contrast, Argentine ants were proficient at both exploitative and interference competition relative to the native ants they displaced and are thus removed from this trade-off. These findings imply that Argentine ants secure a majority of available food resources where this species comes into contact with native ants. Argentine ants may be able to break the competitive trade-off constraining native ants because of their unique colony structure and because they have escaped their natural enemies. The observation that Argentine ants are uncoupled from the competitive trade-off constraining native ants may provide a general explana...

Genetic diversity, asymmetrical aggression, and recognition in a widespread invasive species

“…1A, red circles), and workers, queens, and brood can be transferred freely among nest sites throughout the supercolony (20,23,24,27). The resulting decline in aggression and intraspecific competition likely allows introduced Argentine ant populations to achieve high densities (28) and displace many species of native ants (29)(30)(31)(32). Rarely, smaller supercolonies can be found in the introduced range (20,(22)(23)(24)(25).…”

Resource discovery in ant communities: do food type and quantity matter?

“…In temperate ant communities, the majority of species are omnivores, competing for the same resource pool of insect and plant matter (Vepsäläinen & Pisarski, 1982;Fellers, 1987;Hölldobler & Wilson, 1990;Retana & Cerdá, 1994;Morrison, 1996;Holway, 1999;Fiedler et al, 2007). They are also, with few exceptions, central-place foragers (Hölldobler & Wilson, 1990) that specialise on different components of foraging success, trading off between discovery (resource encounter) and dominance (resource harvest and control) abilities (Vepsäläinen & Pisarski, 1982;Fellers, 1987;Morrison, 1996;Davidson, 1998;Holway, 1999;.…”

“…They are also, with few exceptions, central-place foragers (Hölldobler & Wilson, 1990) that specialise on different components of foraging success, trading off between discovery (resource encounter) and dominance (resource harvest and control) abilities (Vepsäläinen & Pisarski, 1982;Fellers, 1987;Morrison, 1996;Davidson, 1998;Holway, 1999;. In the traditional interpretation of the trade-off, good discoverers are subordinate species that maximised their resource encounter rates so as to access resources before being displaced from them by behavioural dominants during harvest (Vepsäläinen & Pisarski, 1982;Fellers, 1987;Morrison, 1996).…”

“…Dominant species are often characterised by chemical weaponry (Fellers, 1987;Davidson, 1998), large colony size (Holway, 1999), the presence of a morphologically specialised soldier caste (Wilson, 1975(Wilson, , 1976Wilson, 1978;Morrison, 2000), and large body size (Fellers, 1987). They can also maintain resource control via high tempo movement (Davidson, 1998) or by recruiting large numbers of small workers to resources using pheromone trails (Holway, 1999). Presumably, dominant species trade off investment in foragers that can usurp and/or control resources at the expense of having scouts available to find it first (Johnson et al, 1987), although empirical support for this mechanism is lacking.…”

Competition-driven speciation in cichlid fish

“…Specifically, experimental evidence of competition's role in speciation has remained elusive 8,9 . This is despite the concept being implicit in the work of Darwin 10 , evidence that competition for limited resources can restrict habitat use and geographic overlap of species [11][12][13] , and signs that competition can drive divergent eco-phenotypic character displacement where closely related lineages occur in sympatry 14,15 .…”