Biological invasions are a form of global change threatening biodiversity, ecosystem stability, and human health, and cost government agencies billions of dollars in remediation and eradication programs. Attempts to eradicate introduced species are most successful when detection of newly established populations occurs early in the invasion process. We review existing and emerging tools -specifically environmental DNA (eDNA), chemical approaches, remote sensing, citizen science, and agency-based monitoring -for surveillance and monitoring of invasive species. For each tool, we consider the benefits provided, examine challenges and limitations, discuss data sharing and integration, and suggest best practice implementations for the early detection of invasive species. Programs that promote public participation in large-scale biodiversity identification and monitoring (such as iNaturalist and eBird) may be the best resources for early detection. However, data from these platforms must be monitored and used by agencies that can mount appropriate response efforts. Control efforts are more likely to succeed when they are focused on early detection and prevention, thereby saving considerable time and resources.

Abstract. Lack of shared evolutionary history reduces the expectation that native prey will detect and respond to invasive predators. Four mechanisms may explain the adaptive response that is nevertheless seen in various systems: prey may perceive the invasive predator through cue similarity with preexisting predators, cues of conspecifics eaten by the invasive predator, a learned response based on experience with the invasive predator (e.g., cue association), and cues from the invasive predator that are specific to it. We performed laboratory experiments in which zooplankton (Daphnia mendotae) responded adaptively to the zooplanktivore Bythotrephes longimanus (migrating downward), showed no response to taxonomically similar predatory cladocerans, and responded adaptively to more taxonomically distant native fish (migrating downward) and native shrimp (migrating upward). Conspecific cues associated with Bythotrephes predation actually reduced the response of D. mendotae to Bythotrephes. Combined with previous experiments that rule out learning, our experiments rule out the first three mechanisms above, demonstrating that D. mendotae respond to cues specific to and produced directly by Bythotrephes. This finely tuned response may be retained from an ancestral species that coevolved with Bythotrephes in its native range, or may have rapidly evolved due to strong selection by the invasive predator.