Native invaders – challenges for science, management, policy, and society

© The Ecological Society of America www.frontiersinecology.org B invasions, which join synergistically with habitat loss and fragmentation, climate change, natural resource overexploitation, pollution, and a multitude of other anthropogenic factors, are recognized as a leading threat to freshwater, marine, and terrestrial systems. The common notion of an invasive species is one that has become established in a new area and has a measured impact on the ecology and economy of the recipient ecosystem (Valéry et al. 2009). The terminology used to describe invasive species (also commonly called foreign, alien, or exotic species; see Valéry et al. 2008) has led to the perception that these organisms only originate from far-away regions and are transplanted vast distances, predominantly via human vectors. Consequently, most scientific research, management, and policy efforts associated with mitigation focus on invasive species that have been transplanted from the distant regions where they originated (Wilson et al. 2009). Also common but less recognized are species that have become “invasive” in their own native range – these are aptly named “native invaders” (Simberloff 2011). Human activities may create native invaders in three ways. First, human-mediated environmental change facilitates population growth of native species via elevated survivorship and reproduction. The abundance or biomass of a native species can increase to extreme levels, beyond those previously observed, resulting in complete dominance of the community (Goodrich and Buskirk 1995; Valéry et al. 2008). Second, habitat modification or other changes in the environment may increase the per-capita effect of native species on the resident community, leading to predation and competition that exceed natural levels (Didham et al. 2007). In both cases, native species dominate the community by exploiting niche opportunities created by human activities and/or vacancies resulting from the loss or decline of other native species (Simberloff 2011). Third, human activities, such as intentional stocking, establish new populations of native species within the indigenous distribution where they evolved (Hirner and Cox 2007), thus filling their range without increasing the overall extent of that range. Such invasions often go undetected but they can have considerable effects on recipient ecosystems. Both dominant and range-filling native invaders reflect notable shifts from the past as a result of human activities, and in neither case does the introduction event involve the breaching of a major biogeographic boundary. Native species can cause similar harmful ecological and economic impacts to those commonly associated with non-native invasive species (ie the subset of non-native REVIEWS REVIEWS REVIEWS