The spread of invasive species and infectious disease as drivers of ecosystem change

T increased connectivity of the global human population has amplified the frequency and effect of biological invasions and disease outbreaks. New trade routes among previously disconnected countries (Aide and Grau 2004) as well as enhanced transportation technology (eg airplanes and barges) have increased both the frequency and magnitude of invasions and potentially deadly disease outbreaks worldwide. In addition, land-use and climate change interact with human transportation networks to facilitate the spread of invasive species, vectors, and pathogens from local to continental scales (Dukes and Mooney 1999; Sakai et al. 2001; Benning et al. 2002; Patz et al. 2004; Smith et al. 2007). The introduction of nonnative species and range expansions of native species with changing land use and climate may have profound consequences for the ecosystems they occupy. Invasive species drive ecological dynamics at multiple spatial scales and levels of organization, through local and regional extinctions of native species (eg chestnut blight; Mack et al. 2000) and entire communities, shifts in native species richness and abundance (Parker et al. 1999), and altered fire regimes, water quality, and biogeochemical cycles (D’Antonio and Vitousek 1992; Vitousek et al. 1996; Strayer et al. 1999; Bohlen et al. 2004). Invasive species are the second leading cause (after human population growth and associated activities) of species extinction and endangerment in the US (Pimentel 2002). An estimated cost of non-native species in the US alone is over $120 billion annually (Pimentel et al. 2005). Because climate change and land use can exacerbate the spread and effects of invasive species across scales (Dukes and Mooney 1999; Simberloff 2000), identifying invasion and curtailing the spread of invaders is an enormous ecological and societal challenge (Lodge et al. 2006). Several recent reviews of invasive species and disease focus on modeling spatial spread (Hastings et al. 2005), species interactions and ecosystem processes (Lovett et al. 2006), evolutionary change (Strayer et al. 2006), and policy recommendations (Lodge et al. 2006). The objectives of this review are (1) to frame questions and hypotheses CONNECTIVITY CONNECTIVITY CONNECTIVITY