Aridity-Based Assessment of GBIF Occurrence-Record Coverage for Selected Iberian Dryland-Associated Species

Open biodiversity occurrence databases are widely used in ecological and conservation analyses, but their interpretation may be affected by uneven sampling effort, spatial clustering, duplicate records, and incomplete environmental representation. These issues are relevant in drylands, where occurrence records may unevenly represent aridity gradients after being linked to environmental raster data. This study provides an aridity-stratified audit of GBIF occurrence-record coverage for four Iberian species: Testudo graeca, Timon lepidus, Pterocles alchata, and Macrochloa tenacissima. GBIF records from Spain and Portugal for 2000–2025 were cleaned using coordinate, year, country, occurrence-status, geographic sanity, and exact-duplicate filters. Cleaned records were assigned to aridity classes using a global aridity-index raster and compared with the aridity-class composition of the Spain–Portugal study area. Spatial coverage was quantified using occupied 25 km grid cells, grid-size sensitivity checks, and nearest-neighbor distances based on rounded 0.001° unique locations. From 44,451 downloaded records, 31,787 were retained. The study-area background was dominated by semi-arid conditions (59.98%), followed by non-dryland (27.70%), dry sub-humid (11.76%), and arid areas (0.56%). Three species were strongly concentrated in dryland classes: P. alchata (99.98%), M. tenacissima (98.17%), and T. graeca (96.59%), whereas T. lepidus showed broader environmental coverage. These results show that aridity-stratified record audits can provide useful context for interpreting open biodiversity occurrence data.