Chapter 1
Introduction
Invasive species impact ecosystems and the economy. In the United States alone,
control efforts directed at invasive species and environmental damage caused by invasive
species total $137 billion annually (Pimentel et al. 2000). Ants are among the worst
invaders and have caused ecological damage and economic costs worldwide (Lowe et al.
2004). Invasive ants often become highly abundant in their introduced ranges,
outnumbering native ants and reducing native ant diversity (Holway et al. 2002), as well
as affecting other invertebrates and vertebrates such as birds and lizards (Holway et al.
2002, Kenis et al. 2009). Preventing introductions is the most effective way to control
the spread of invasive species, yet non-native ants continue to be accidentally introduced
to new environments around the world. Therefore it is important to study the dynamics
of new introductions in order to assess the risk of widespread invasion and to determine
the most effective methods of control, as resources for controlling invasive species are
often limited.
Despite considerable research on invasive species, one area that needs further
exploration is how established invasive species influence the establishment and spread of
newly introduced species. In some cases, existing invasive species have been shown to
facilitate new invasions, which can lead to invasional meltdown (Simberloff and Von
Holle 1999, O’Dowd et al. 2003, Bourgeois et al. 2005). However, in cases where
established invasive species act as competitors or predators of newly introduced species,
the established species may provide biotic resistance to new invasions (Simberloff and
Von Holle 1999). Nevertheless, very few studies have looked at competition between