GBIF information is not enough: national database improves the inventory completeness of Amazonian epiphytes

Distribution data sharing in global databases (e.g. GBIF) allowed the knowledge synthesis in several biodiversity areas. However, their Wallacean shortfalls still reduce our capacity to understand distribution patterns. Including exclusive records from other databases, such as national ones (e.g. SpeciesLink), could mitigate these shortfall problems, but it remains not evaluated. Therefore, we assessed whether (i) the inventory completeness, (ii) taxonomic contribution and (iii) spatial biases could be improved when integrating both global and national biodiversity databases. Using Amazonian epiphytes as a model, we compared the available taxonomic information spatially between GBIF and SpeciesLink databases using a species contribution index. We obtained the inventory completeness from sources using species accumulation curves and assessed their spatial biases by constructing spatial autoregressive models. We found that both databases have a high amount of exclusive records (GBIF: 36.7%; SpeciesLink: 21.7%) and species (17.8%). Amazonia had a small epiphyte inventory completeness, but it was improved when we analyzed both databases together. Individually, both database records were biased to sites with higher altitude, population and herbarium density. Together, river density appeared as a new predictor, probably due to the higher species contribution of SpeciesLink along them. Our findings provide strong evidence that using both global and national databases increase the overall biodiversity knowledge and reduce inventory gaps, but spatial biases may persist. Therefore, we highlight the importance of aggregating more than one database to understand biodiversity patterns, to address conservation decisions and direct shortfalls more efficiently in future studies.