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Key Words ants, biological invasion, indirect effects, interspecific competition
* 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.
INTRODUCTION
Ants play a diversity of roles in terrestrial ecosystems. Ants act as predators, scavengers, herbivores, detritivores, and granivores (Holldobler & Wilson 1990) and participate in an astonishing array of associations with plants and other insects (Beattie 1985, Holldobler & Wilson 1990, Huxley & Cutler 1991, Jolivet 1996). Ants, in turn, are preyed upon by a variety of specialist predators, including reptiles (Pianka & Parker 1975), mammals (Redford 1987), spiders (Porter & Eastmond 1982), and insects (Gotelli 1996) and are host to both dipteran (Feener & Brown 1997) and hymenopteran parasitoids (Heraty 1994). Ants also serve as important agents of soil turnover, nutrient redistribution, and small-scale disturbance (Holldobler & Wilson 1990, Folgarait 1998, MacMahon et al. 2000). For these reasons, and because they can be sampled and identified with relative ease, ants figure prominently in ecological studies and have become a key indicator group in studies of diversity and ecosystem function (Agosti et al. 2000). The widespread success of ants stems in large part from their elaborate social behavior, which is itself a tremendously rich source of information for studies of kin selection, reproductive skew, levels of selection, foraging behavior, and self-organization (Wilson 1971, Holldobler & Wilson 1990, Keller 1993, Bourke & Franks 1995, Crozier & Pamilo 1996).
Invasive ants form a small and somewhat distinct subset of the at least 150 species of ants introduced...