The paradox of persistence: island species as models for conservation.

Species on islands frequently experience founder events and population bottlenecks and are often subject to disturbances that further reduce population sizes. Despite these challenges, some island lineages persist for millennia-the paradox of persistence. Here, we synthesize genomic studies across island systems and show that reported effective population sizes are frequently below 100, but assessments of genetic load and its temporal dynamics remain uncommon. We show that island systems can offer critical insights into how small populations maintain viability and adaptive potential. Future research on genomic erosion needs to broaden taxonomic and geographic coverage, leverage temporal genomic data, and integrate demographic and fitness-based approaches to link evolutionary resilience on islands with the conservation of increasingly fragmented populations worldwide.