The Causes and Consequences of Ant Invasions

Abstract

Key Words ants, biological invasion, indirect effects, interspecific competitions Abstract Invasions by non-native ants are an ecologically destructive phenomenon affecting both continental and island ecosystems throughout the world. Invasive ants often become highly abundant in their introduced range and can outnumber native ants. These numerical disparities underlie the competitive asymmetry between invasive ants and native ants and result from a complex interplay of behavioral, ecological, and genetic factors. Reductions in the diversity and abundance of native ants resulting from ant invasions give rise to a variety of direct and indirect effects on non-ant taxa. Invasive ants compete with and prey upon a diversity of other organisms, including some vertebrates, and may enter into or disrupt mutualistic interactions with numerous plants and other insects. Experimental studies and research focused on the native range ecology of invasive ants will be especially valuable contributions to this field of study. Table 1 lists characteristics of six of the most widespread, abundant, and damaging invasive ants. A great disparity exists with respect to how much is known about each of these species. For example, the red imported fire ant (S. invicta) ranks as one of the most well studied social insects (Ross & Keller 1995, Tschinkel 1998, whereas Anoplolepis gracilipes remains poorly studied by comparison, so much so that its native range is not even known. As an inevitable result of this difference, we devote more attention to the relatively well-known S. invicta and the Argentine ant (Linepithema humile) than to other species but caution against drawing the conclusion that other invasive ants resemble L. humile and S. invicta or pose less TABLE ECOLOGICAL EFFECTS OF ANT INVASIONS 183 INVASIVE ANTS AND THEIR GENERAL CHARACTERISTICS

Genetic diversity and colony breeding structure in native and introduced ranges of the Formosan subterranean termite, Coptotermes formosanus

“…Bottlenecks can only be detected across a few dozen generations (Luikart et al 1998). Yet there is a lingering effect in the form of reduced genetic diversity (Holway et al 2002;Tsutsui et al 2000) unless repeated introductions from multiple, genetically distinct source populations counteract the effect of genetic bottlenecks connected to each single introduction. However, genetically diverse introduced populations, such as populations of the paper wasp in the USA (Johnson and Starks 2004), are the exception.…”

“…In invasive Hymenoptera, low genetic diversity is believed to be the reason for low intraspecific aggression, which in extreme cases leads to unicoloniality, i.e., the formation of large supercolonies that dominate the introduced range (Holway et al 2002;Tsutsui et al 2000Breton et al 2004;Suarez et al 2008;Fournier et al 2009). In addition, frequent occurrence of polygyny and colony propagation by budding could facilitate spread of invasive species after introduction .…”

Ant communities (Hymenoptera: Formicidae) in an urban ecosystem near the Atlantic Rainforest

“…Tramp ants are species that are intimately associated with human activities, and generally nest in structures built in urban environments (Schultz and McGlynn, 2000). They share characteristics that facilitate their introduction into new environments, such as generalist feeding habits, polygamy, reduced intra-specific aggression, small size, and high recruitment, as well as having a high rate of migration, uni-colonial population, abolition of nuptial flight, and very small workers and queens (Passera, 1994;Holway et al, 2002).…”

An Alpine ant’s behavioural polymorphism: monogyny with and without internest aggression inTetramorium alpestre

“…They are extensive cooperative units with many queens and very many workers integrated harmoniously over several square metres to many square kilometres (Crozier & Pamilo 1996; Giraud et al 2002; Steiner et al 2009). Supercoloniality is often considered key to the success of invasive ant species (Holway et al 2002), and supercolonies have been thoroughly studied over the last decades (Tsutsui et al 2000; Giraud et al 2002; Pedersen et al 2006; Leniaud et al 2011; Huszar et al 2014; Kennedy et al 2014). However, the factors triggering their emergence remain largely unknown (Suarez & Suhr 2012).…”