Interspecific displacement mechanisms by the invasive little fire ant Wasmannia auropunctata

Abstract

Competition between invasive species and native ones in the new environment was found to be significant and to affect both animal and plant species. Invasive ants are notorious for displacing local ant species through competition. Competitive displacement of native species can occur through interference and or resource competition. However, for invasive ants, little is known about the relative importance of competitive displacement. We studied competitive interactions of the little fire ant, Wasmannia auropunctata, one of the most destructive invasive ant species, with two other ant species, Monomorium subopacum and Pheidole teneriffana. We compared the species' foraging behavior and studied their aggressive interactions around food baits for the short (2 h) and long (21 days) term in the laboratory. Surprisingly we found that in short term experiments W. auropunctata had the poorest foraging abilities of the three species studied: it took the workers the longest to locate the bait and retrieve it; in addition they retrieved the lowest amount of food. When both W. auropunctata and M. subopacum were foraging the same bait, in the short term competition experiment, W. auropunctata workers did not defend the bait, and ceased foraging when encountered with competition. The long-term experiments revealed that W. auropunctata had the advantage in aggressive interactions over time; they eliminated seven of nine M. subopacum's nests while consuming some of the workers and brood. According to our laboratory studies, W. auropunctata cannot be considered an extirpator species, unless it has a substantial numerical advantage, in contrast with previous assumptions. Otherwise it may behave as an insinuator species, i.e. the workers do not initiate aggression and by staying undetected they can continue foraging adjacent to dominant species.

From insinuator to dominator: Foraging switching by an exotic ant

“…While these studies shed considerable light on invasion processes, we lack similar detailed studies of other exotic ant species, in particular W. auropunctata , between their native and introduced home range (McGlynn, ). Recent work by Vonshak, Dayan, and Hefetz () investigated the competitive interactions between W. auropunctata and native ant species in a laboratory setting. They found that over a short time span (2 hr), W. auropunctata had the poorest foraging abilities (i.e.…”

“…time to discovering, retrieving and defending resources) when worker densities were low. However, over 21 days W. auropunctata rebounded and displaced the other ant species by raiding their nests (Vonshak et al., ). One explanation is that W. auropunctata behaves as an “insinuator” species, in which workers do not display aggression at low worker densities enabling them to forage undetected alongside dominant ant species.…”

Food Webs in the Litter: Effects of Food and Nest Addition on Ant Communities in Coffee Agroecosystems and Forest

“…Even with W. auropunctata data points removed, habitat type remained an important factor for colony growth rate (F 2,160 ϭ 4.853; P ϭ 0.009). Although several mechanisms might explain how W. auropunctata may have limited growth of other ant species within the high-shade coffee, one recent study points to a potential mechanism whereby W. auropunctata invade nests of other species and consume their workers and brood (Vonshak et al 2012). Thus, W. auropunctata may have preyed on individuals of other species, leading to increased colony growth after other ants harvested added food.…”

Resource competition assays between the African big‐headed ant, Pheidole megacephala (Fabricius) and the invasive Argentine ant, Linepithema humile (Mayr): mechanisms of inter‐specific displacement

“…Numeric dominance has been cited in numerous studies on invasive ants as the most important factor promoting the success of these ants (Holway et al, 2002a;O'Dowd et al, 2003;Abbott et al, 2007;Rowles & O'Dowd, 2007;Vonshak et al, 2012). However, invasive ant species first arrive within a recipient environment as small propagules and do not have this numeric dominance (Hee et al, 2000;Holway et al, 2002a;Tillberg et al, 2007).…”

“…Many of these studies are largely based on bait sampling and generalisations with regards to biological characteristics of invasive ants as measures to predict invasion success (Holway, 1999;Richardson et al, 2000;Holway et al, 2002b). However, detailed studies on the direct interactions between native ants and invasive ants are wanting, and are needed to understand how invasive ant species colonise new environments and which of their biological traits are likely to enhance their invasion success (Blight et al, 2010;Vonshak et al, 2012). For L. humile, the combination between abiotic conditions and inter-specific competition from native ant species may limit the extent to which these ants invade new environments as small propagules, largely because niche availability and suitability is determined by abiotic factors as well as the presence of competitive dominant ant species (Holway, 1999;Thomas & Holway, 2005;Walters & Mackay, 2005).…”