Dr. Anthony Ricciardi McGill University Incorporating time-since-invasion into invasion science and risk assessment Although considerable management attention is given to non-native species, invasions are essentially population-level events. Owing to the influence of the environment and other context dependencies on introduced populations, the impacts of non-native species vary across space and time. Climate warming of inland waters have imposed a universal stressor that is expected to alter species interactions and the impacts of invaders on food webs; the magnitude and direction of these alterations has both fundamental and applied importance to ecology. Time-since-invasion is also recognized as a mediator of impact but has not yet been well integrated into invasion theory and is virtually absent from consideration in risk assessment. Here I review evidence from aquatic case studies that evaluates the role of time-since-invasion in invasion dynamics, especially the phenomena of i) higher impacts at the leading edge of spreading populations, and ii) time lags, especially the ‘sleeper populations’—i.e., apparently innocuous non-native populations that are subsequently triggered to become invasive by an external factor or stressor that alters the physical or biological environment. Theory needs to be further developed to explain and predict spatiotemporal variation in population outbreaks and their impacts, especially in the context of climate change.
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