A common characteristic of islands is the relative simplicity
of their biotic communities, providing tractable systems for
analyses of biological invasions (Vitousek 2002). Changes
in the abundance of species affect the structure and
functioning of ecosystems (Chapin et al. 1997), and both
retrospective reconstruction of impacts (Fritts & Rodda
1998) and experimental additions of invaders (Schoener &
Spiller 1999) illustrate that single consumer species can
have wide-ranging direct and indirect effects on island
communities. These effects are especially evident on
Christmas Island because the dominant native omnivore,
the red land crab, is deleted by the ant invader. In the
absence of ant invasion, these crabs are abundant,
occurring at densities of up to 1.8 m
)2 and 1500 kg ha
)1
(Green 1997).