Behavioural plasticity associated with propagule size, resources, and the invasion success of the Argentine ant Linepithema humile

Abstract

Summary 1.The number of individuals involved in an invasion event, or 'propagule size', has a strong theoretical basis for influencing invasion success. However, rarely has propagule size been experimentally manipulated to examine changes in invader behaviour, and propagule longevity and success. 2. We manipulated propagule size of the invasive Argentine ant Linepithema humile in laboratory and field studies. Laboratory experiments involved L. humile propagules containing two queens and 10, 100, 200 or 1000 workers. Propagules were introduced into arenas containing colonies of queens and 200 workers of the competing native ant Monomorium antarcticum . The effects of food availability were investigated via treatments of only one central resource, or 10 separated resources. Field studies used similar colony sizes of L. humile , which were introduced into novel environments near an invasion front. 3. In laboratory studies, small propagules of L. humile were quickly annihilated. Only the larger propagule size survived and killed the native ant colony in some replicates. Aggression was largely independent of food availability, but the behaviour of L. humile changed substantially with propagule size. In larger propagules, aggressive behaviour was significantly more frequent, while L. humile were much more likely to avoid conflict in smaller propagules. 4. In field studies, however, propagule size did not influence colony persistence. Linepithema humile colonies persisted for up to 2 months, even in small propagules of 10 workers. Factors such as temperature or competitor abundance had no effect, although some colonies were decimated by M. antarcticum . Synthesis and applications.Although propagule size has been correlated with invasion success in a wide variety of taxa, our results indicate that it will have limited predictive power with species displaying behavioural plasticity. We recommend that aspects of animal behaviour be given much more consideration in attempts to model invasion success. Secondly, areas of high biodiversity are thought to offer biotic resistance to invasion via the abundance of predators and competitors. Invasive pests such as L. humile appear to modify their behaviour according to local conditions, and establishment was not related to resource availability. We cannot necessarily rely on high levels of native biodiversity to repel invasions.

A neurotoxic pesticide changes the outcome of aggressive interactions between native and invasive ants

“…In New Zealand, for instance, the invasive Argentine ant is only found in urban and agricultural settings co-occurring (and possibly competing for food sources) with the native Southern ant [20,23]. In these areas, pesticides such as neonicotinoids are commonly used to control insect pests and may affect ants via distinct pathways such as direct contact with the active ingredient applied in the environment, consumption of plant material containing the pesticide or even ingestion of honeydew produced by mutualists.…”

“…Competition for resources substantially influences the success and fitness of many organisms, including social insects such as ants [18]. The ability of ants to compete for resources is frequently related to their colony size and behavioural plasticity [20]. Thus, the modification of behaviour and learning may have broad effects on communities [15].…”

“…The Southern ant is abundant and widespread within New Zealand [24]. Both species have similar habitat and food preferences, and are aggressive towards each other [20,24], making them an ideal model to evaluate the effects of neonicotinoid pesticides on interacting species. We first assessed the effects of sublethal doses of a neonicotinoid on workers and colonies of each species.…”

Efficacy of NaCl brine for treatment of ballast water against freshwater invasions

“…Propagule size is the number of individuals in a release event and propagule number is the number of release events. As propagule size and number increase, the probability of successful invasion also increases because as more individuals are introduced into one place, it becomes more likely that some individuals will be successful in establishing colonies and thrive in the new environment (Kolar and Lodge, 2001;Lockwood et al, 2007;Sagata and Lester, 2008). The condition of propagules also contributes to the success rate of biological invasions in that the healthier the invaders are, the more likely that they will survive long enough to find food and suitable mates and contribute to the success rate of establishment (Simberloff, 2009).…”

Elton's insights into the ecology of ant invasions: lessons learned and lessons still to be learned

“…However, there have been few tests of the role of propagule pressure or size in ant invasions. Recently, Sagata and Lester (2009) showed experimentally that neither propagule size (the size of the ' invading ' colony) nor resource availability consistently predicted invasion success by L. humile . They went on to suggest that the ability of L. humile to modify its behaviour according to local conditions will all but rule out the ability to predict whether a site will be invaded, based simply on resource availability or characteristics of the native community at that site (Sagata & Lester 2009 ).…”