Patterns of spread in biological invasions dominated by long-distance jumpdispersal: Insights from Argentine ants

Invading organisms may spread through local movements (giving rise to a dif fusion-like process) and by long-distance jumps, which are often human-medi ated. The local spread of invading organisms has been fit with varying succ ess to models that couple local population growth with diffusive spread, bu t to date no quantitative estimates exist for the relative importance of lo cal dispersal relative to human-mediated long-distance jumps. Using a combi nation of literature review, museum records, and personal surveys, we recon struct the invasion history of the Argentine ant (Linepithema humile), a wi despread invasive species, at three spatial scales. Although the inherent d ispersal abilities of Argentine ants are limited, in the last century, huma n-mediated dispersal has resulted in the establishment of this species on s ix continents and on many oceanic islands. Human-mediated jump dispersal ha s also been the primary mode of spread at a continental scale within the Un ited States. The spread of the Argentine ant involves two discrete modes. M aximum distances spread by colonies undergoing budding reproduction average d 150 m/year, whereas annual jump-dispersal distances averaged three orders of magnitude higher. Invasions that involve multiple dispersal processes, such as those documented here, are undoubtedly common. Detailed data on inv asion dynamics are necessary to improve the predictive power of future mode ling efforts.