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<p>The terrestrial molluscan fauna of the Caatinga Dominion, a seasonally dry tropical region in north-eastern Brazil, remains one of the least-documented components of its biota, thereby limiting its inclusion in ecological, biogeographical and conservation assessments. Here, we present a diagnosis of Caatinga terrestrial molluscs by addressing three questions: how much diversity is currently known, how strongly available records are spatially biased, and how sensitive species visibility is to minimum-occurrence thresholds commonly applied in spatial analyses. We compiled 944 records representing 155 species, 62 genera and 25 families. Stylommatophora accounted for 141 species (91%), highlighting the great taxonomic concentration of the known fauna. Despite this apparent richness, records were sparse and unevenly distributed.&#xa0;Only 221 of 8,761 grid cells (2.5%) contained records, whereas 8,443 cells (97.4%) lay within the expected occupancy area but lacked any record. Mean sampling completeness per cell, measured as the ratio between observed and expected richness, was 0.003, and observed–expected overlap was low (Jaccard = 0.0255). Species retained under increasing occurrence thresholds declined from 88 at t = 3 to one at t = 38, revealing pronounced taxonomic invisibility. These patterns may directly affect conservation planning and the reliability of spatial analyses that depend on minimum occurrence thresholds.</p>

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Taxonomic invisibility and knowledge shortfalls in terrestrial molluscs of the Caatinga Dominion, a seasonally dry tropical region

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月24日

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  • Emerson Santos Castro,
  • Edenísio Zacarias Galvão Costa,
  • Edson Lourenço da Silva,
  • Rodrigo Brincalepe Salvador,
  • Tamaris Gimenez Pinheiro

摘要

The terrestrial molluscan fauna of the Caatinga Dominion, a seasonally dry tropical region in north-eastern Brazil, remains one of the least-documented components of its biota, thereby limiting its inclusion in ecological, biogeographical and conservation assessments. Here, we present a diagnosis of Caatinga terrestrial molluscs by addressing three questions: how much diversity is currently known, how strongly available records are spatially biased, and how sensitive species visibility is to minimum-occurrence thresholds commonly applied in spatial analyses. We compiled 944 records representing 155 species, 62 genera and 25 families. Stylommatophora accounted for 141 species (91%), highlighting the great taxonomic concentration of the known fauna. Despite this apparent richness, records were sparse and unevenly distributed. Only 221 of 8,761 grid cells (2.5%) contained records, whereas 8,443 cells (97.4%) lay within the expected occupancy area but lacked any record. Mean sampling completeness per cell, measured as the ratio between observed and expected richness, was 0.003, and observed–expected overlap was low (Jaccard = 0.0255). Species retained under increasing occurrence thresholds declined from 88 at t = 3 to one at t = 38, revealing pronounced taxonomic invisibility. These patterns may directly affect conservation planning and the reliability of spatial analyses that depend on minimum occurrence thresholds.