Environmental thresholds in canopy cover shape spider assemblages in Cerrado riparian zones

Riparian zones in the Brazilian Cerrado are increasingly threatened by agricultural expansion, deforestation, and land-use change, with significant implications for biodiversity conservation. Spiders are ecologically important predators and bioindicators, yet little is known about how they respond to changes in vegetation structure in riparian habitats. This study aims to assess the influence of canopy cover and understory complexity on the diversity, abundance, and composition of understory spider assemblages in riparian zones. We sampled 3260 adult spiders across 30 first- to fourth-order streams in the Cerrado, using standardized beating tray methods, and measured habitat structure variables. Our results showed that canopy cover had a positive effect on spider abundance and species richness, while understory complexity was significantly related only to species richness. Vegetation structure had a limited effect on species composition. Using threshold indicator taxa analysis (TITAN), we identified ecological thresholds for canopy cover between 58 % and 77 %, and 16 spider taxa were classified as indicators of change along this gradient. The study demonstrates that canopy cover is a significant driver of spider diversity and that threshold-based metrics can help identify sensitive points of ecosystem change.Implications for insect conservation: Riparian zones in the Cerrado biome should be prioritized for conservation and restoration, especially where canopy cover has been markedly diminished. Preserving canopy cover above 60 % is likely essential to maintain both the structural integrity and functional dynamics of understory spider assemblages. As reliable bioindicators at species and community levels, spiders can effectively reflect riparian habitat quality. Therefore, conservation strategies ought to encompass restricting deforestation along riparian margins, enforcing buffer-zone regulations and reestablishing native vegetation to enhance habitat complexity. These measures are crucial not only for protecting spider diversity but also for sustaining the ecosystem services they provide, such as natural pest control and trophic regulation at the aquatic–terrestrial interface.