Lag times and exotic species: The ecology and management of biological invasions in slow-motion1

:Time lags can be found throughout the invasion process, including in the arrival, establishment, and impacts of invaders. While we often lack the information necessary to generate quantitative expectations of invader performance, some types of lags are not surprising. For example, populations often grow exponentially in the early phases of invasion, and this will give rise to an inherent lag. More broadly, early rates of anthropogenic invasion were much slower than what we are now witnessing, but as the vectors of invasion have also increased dramatically over time, this early lag is not unexpected. Many other lags, however, appear dramatically prolonged, and can come to an end with changes to the invader or its environment. For example, exotics can exist in relatively low numbers for decades before exploding, or invaders can become more aggressive over time and increase their impacts on native species. Invasion-related lags are critical for our efforts to manage invaders, as they may lead us to make inaccurate assessments of the risks posed by invaders as well as miss critical windows for action. Recognition of the phenomenon of long lags before sudden changes in invader dynamics also suggests that we adopt a strict precautionary principle: we should assume that any invader has the potential for undesirable effects and that long periods of seemingly consistent behaviour can be poor predictors of what invaders will do in the future.