Can Hormesis Facilitate Biological Invasions?

During biological invasions, introduced organisms are exposed to multiple, sequential environmental stressors across invasion stages. Although stress is traditionally viewed as a source of damage and environmental filtering, exposure within a hormetic zone may induce a persistent state that improves performance under subsequent challenges. Here, we critically review the available evidence for stress-induced hormesis in invasion-relevant contexts. We then develop a four-stage framework linking hormetic exposure to persistent state changes, improved performance under subsequent stress, and ultimately increased establishment. Importantly, the framework posits that stress-induced hormesis can facilitate invasions when its effects are maintained across all four stages and ultimately translated into demographic outcomes. Building on this framework, we propose the Hormesis-Enhanced Propagule Quality Hypothesis, which defines propagule quality as a dynamic, stress-responsive property. The hypothesis emphasizes that hormetic effects on fitness-related traits can enhance establishment success, particularly when populations are near demographic or Allee-effect thresholds. When retained across generations, these effects may stabilize founder lineages during vulnerable early population growth and increase colonization yield. However, hormetic responses are inherently context-, endpoint-, and time-dependent, may involve endpoint-specific trade-offs or cross-susceptibility, and may provide diminished or no benefit under environmental mismatch. We therefore outline research priorities for determining when transient stress responses scale to population- and community-level invasion outcomes. These priorities include sequential-stress experiments, multigenerational lineage tracking, multi-omics, and demographic modeling. The four-stage framework and hypothesis advance invasion theory by identifying stress-modified propagule quality as a previously overlooked determinant of establishment success, with potential implications for predicting and managing invasive species.