Invasion lags: The stories we tell ourselves and our inability to infer process from pattern

Aim: Many alien species experience a lag phase between arriving in a region and becoming invasive, which can provide a valuable window of opportunity for management. Our ability to predict which species are experiencing lags has major implications for management decisions that are worth billions of dollars and that may determine the survival of some native species. To date, timing and causes of lag and release have been identified post hoc, based on historical narratives. Location: Global. Methods: We use a simple but realistic simulation of population spread over a fragmented landscape. To break the invasion lag, we introduce a sudden, discrete change in dispersal. Results: We show that the ability to predict invasion lags is minimal even under controlled circumstances. We also show a non-negligible risk of falsely attributing lag breaks to mechanisms based on invasion trajectories and coincidences in timing. Main conclusions: We suggest that post hoc narratives may lead us to erroneously believe we can predict lags and that a precautionary approach is the only sound management practice for most alien species.