ond, time lags for species extinction must be better studied. Time lags to extinction have received very limited attention. Some important work was done by Diamond (1972), and a smattering of more recent papers exist (Brooks et al., 1999), but here too the bulk of attention has been on birds. A greater effort is needed to understand dynamics of time lags to extinction, particularly how these may vary across taxonomic groups and geographic areas. Third, we need to more carefully consider and examine how exotic invasions change the abundance patterns of native species. Although abundance for most native species is expected to decline after invasions, the patterns of these declines may be very important in predicting whether extinctions are likely in the future. In particular, it is important to know which species pay the largest cost; the long-term consequences will differ greatly if most of the abundance declines in native species are borne by those species that were previously most abundant, as opposed to those species that were already naturally rare. Fourth, we need to understand how the transformation of large areas into exotic-dominated ecosystems influences extinction of native species through reduction in total available habitat. The species–area relationship is currently one of the most actively used tools for predicting species loss (Gurevitch and Padilla, 2004), yet its application to exotic-dominated habitat loss has been poorly studied. It is unclear whether the species–area relationship can be used in such circumstances to predict future species loss and, if so, then how accurate such predictions are likely to be. The answer is likely to depend on the extent to which patterns of area loss are congruent with species distributions (Seabloom et al., 2002) and on the degree to which natives are excluded from exotic-dominated habitats. Collectively, these gaps in our knowledge create large uncertainty in forecasts of the future responses of island biotas to species introductions. Certainly, there is a pressing need for new data and insights if we cannot distinguish among the polar extremes of (i) there is little risk to native plant species on islands from future exotic introductions and (ii) a large fraction of native plant species on islands are already on a path to extinction. Hopefully, future work on the interplay between species invasions and extinctions can more fully resolve these issues and, in the process, help us to develop a more comprehensive theory of species extinctions.
Accounts of all 785 species listed as “extinct” were downloaded from the International Union for Conservation of Nature database (www.iucnredlist.org) in November 2007. Those species comprising the terres-