Data from Castro et al[Taxonomic invisibility and knowledge shortfalls in terrestrial molluscs of the Caatinga Dominion, a seasonally dry tropical region]

This dataset supports the study “Taxonomic invisibility and knowledge shortfalls in terrestrial molluscs of the Caatinga Dominion, a seasonally dry tropical region”. We analyse whether the currently available occurrence data for Caatinga terrestrial molluscs are insufficient to represent the known and expected spatial distribution of the group, and whether many species become analytically “invisible” when minimum occurrence-record thresholds are applied.
The dataset contains curated occurrence records and R scripts used to assess observed richness, expected richness, sampling completeness, spatial sampling gaps and species visibility under increasing occurrence thresholds. Occurrence records were compiled from scientific collections, GBIF, and the published literature, then taxonomically standardised and spatially filtered to retain valid records of terrestrial molluscs in the Caatinga Dominion, north-eastern Brazil.
The data show that 155 terrestrial mollusc species, belonging to 62 genera and 25 families, are currently documented from 944 occurrence records inside the Caatinga Dominion. However, these records are highly sparse and spatially uneven. Only a small fraction of 10 km grid cells contain occurrence records, whereas most cells are included in the expected-occupancy area but lack any formal record. The outputs also show very low sampling completeness, low overlap between observed and expected richness, and a rapid decline in the number of species eligible for spatial analyses as the minimum occurrence threshold increases.
Expected richness should be interpreted as a standardised, data-driven hypothesis of potential occupancy. It was derived from simple geometric occupancy envelopes, using buffers for poorly recorded species and concave hulls for species with enough records to construct polygons. These outputs are intended to support reproducibility, transparency and future studies on biodiversity knowledge shortfalls, spatial sampling gaps and conservation planning for terrestrial molluscs in tropical dry regions.