Phenological Trends and Projected Climatic Suitability of Five Wool Carder Bees of the Genus Anthidium Across the Mediterranean Basin

Climate change may alter both the timing of bee activity and the climatic suitability of bee habitats, risking plant–pollinator mismatches, yet such effects are rarely assessed for Mediterranean bees. We analysed 4103 occurrence records (1980–2024) of five wool carder bee species (Anthidium) to evaluate first-flight trends and to project changes in climatically suitable areas for 2081–2100 using ensemble species distribution models driven by five general circulation models. Non-stationary phenological dynamics were detected in four species. Only A. florentinum showed a robust advance in first-flight timing of 10.0 days per decade that remained significant after False Discovery Rate (FDR) correction (q < 0.001), whereas the advance in A. loti was not significant (q = 0.082). The advance in A. florentinum persisted when only Iberian records were analysed. Under the SSP5-8.5 emissions scenario, six of 15 countries met the data-sufficiency criterion; among these, the largest net declines in climatically suitable sampled locations were projected for Spain (−15.3 percentage points), Morocco (−13.7) and Portugal (−12.5), whereas Italy, France and Croatia showed small net gains. Under spatial block cross-validation, model performance was lower than under random cross-validation but remained acceptable by AUC (0.75–0.81). Among countries meeting the data-sufficiency criterion, Morocco, Spain and Portugal exceeded the reference threshold of a Composite Vulnerability Index that combines projected habitat decline, phenological shift and projected warming. These results indicate uneven, country-specific vulnerability and highlight the need to account for non-stationarity, sampling bias and spatial validation when assessing climate risks to Mediterranean pollinators.