Cryptic invasions: A review.

Cryptic invasions are defined as the introduction and spread of non-native lineages within the species' native range (intra-specific cryptic invasion) or the invasion of non-native species that goes unnoticed due to misidentification as a native or another invasive species (inter-specific cryptic invasion). While population-specific attributes are acknowledged to play a critical role in the success and impact of biological invasions in general, our knowledge of the causes and consequences of cryptic invasions is largely neglected. Cryptic invasions are inherently difficult to recognize and, despite being likely widespread, often go undetected. In this review, we analyse the sources, mechanisms, and consequences of cryptic invasions. Using a bibliometric survey, we first quantify the relative proportion of study questions, taxa, and geographic regions. We then highlight the value of comparative information from archived specimens in uncovering the occurrence and timing of cryptic invasions. We examine the mechanisms of cryptic invasions and emphasise the role of anthropogenic environmental changes on the arrival of cryptic invaders. We then discuss the role of interspecific biological interactions in the success of cryptic invasions and the role of hybridization between native and non-native lineages in cryptic invasions. We examine the competitive advantage of some invasive lineages in key physiological, ecological or sexually-selected traits. We argue that cryptic invasions, often undetected, may trigger subsequent rapid range expansions. We suggest that cryptic invasions are much more common than currently acknowledged. We highlight the role of coevolved associations (host-parasite, mutualism, herbivory), inherently population-specific, in the impacts of cryptic invasions on local communities. Finally, we outline a framework to manage intraspecific cryptic invasions.