Testing Climatic Stability–Endemism Relationships Using Western Balkan Endemic Beetles’ Localities and Paleoclimate Reconstructions

An association between long-term climatic stability and endemism has been suggested, but it has been tested in plants and vertebrates rather than invertebrates. Using high-resolution paleoclimate reconstructions (CHELSA-TraCE21k; 21,000 BP–present), we tested whether non-cave localities of endemic beetles in the western Balkans are non-randomly associated with local climatic stability. For four bioclimatic variables, we quantified temporal variability using three metrics (SD, range, detrended SD) and defined stability islands as cells in the most stable quartile relative to their neighbourhood at three spatial scales (3 × 3, 5 × 5, 9 × 9). We tested whether 578 endemic-locality cells were enriched in stability islands, against elevation-matched null models. Annual mean temperature produced the highest raw frequency of endemic localities in stability islands, but this pattern was not significant after elevation control. In contrast, endemic localities showed a modest but consistent enrichment in annual precipitation stability islands (observed 9.7–10.7% vs. null 7.3–8.5%; p = 0.01–0.03) across neighbourhood sizes. At the 3 × 3 scale, 60 endemic localities fell within precipitation-stability islands; of them, 20 were outside current protected areas—indicating conservation gaps where minor boundary revisions could enable protection of endemic beetles’ habitats in precipitation-stable sites.