Secondary pathways are an important, but neglected aspect of biological invasions

Susan Canavan, Evelyn M Beaury, Katelyn T Faulkner, Kim Canavan, Diana Albuja, Wesley Daniel, Leah Elwell, Peder Engelstad, Leigh Greenwood, Heidi Himes, Catherine S Jarnevich, Ivan Jaric , Amy Kendig, Julie L Lockwood, Charles W Martin, Heidi McMaster, Laura Meyerson, Kathryn A O'Shaughnessy, Elliott W Parsons, Alanna D Richman, Katriona Shea, Daniel Simberloff, Helen R Sofaer, Rochelle Sturtevant, Amanda Suzzi-Simmons, Ahmed Taheri , Emma van der Heide, Ava Waine, Deah Lieurance

The pathways through which non-native species are introduced and spread help shape the rate and geographic patterns of biological invasions. These pathways can be classified as primary, where non-native species cross jurisdictional or biogeographic boundaries, or secondary, where species move within these boundaries after introduction. Despite fundamental economic, political, social, and ecological differences between these pathway types that affect the risk of species introductions and the prioritization of management responses, most classification schemes and regulatory frameworks do not explicitly distinguish between them. This lack of distinction is consequential: primary pathways are relatively well-defined and subject to biosecurity regulation, while secondary pathways remain poorly characterized and largely overlooked in policy and practice. Secondary pathways create multiple nodes from which non-native species spread, transporting individuals extensively and complicating containment efforts. Here we refine the distinction between primary and secondary pathways and explore their explicit separation in classification and management frameworks. We highlight how failing to recognize this distinction can limit the effectiveness of biosecurity systems, particularly by leaving secondary pathways inadequately addressed. Explicitly distinguishing these pathway types can help to improve invasive species control responses, strengthen cross-scale coordination efforts, reduce economic damage, and achieve global biodiversity goals.