Lizards at the Crossroads: How Microclimate and Habitat Structure Drive Species Turnover in a Neotropical Ecotone

ABSTRACT Ecotones are dynamic transition zones where environmental heterogeneity can shape community assembly. We investigated how habitat structure and microclimatic variation influence lizard abundance, richness and species turnover across a fine‐scale gradient from open savanna to seasonally dry forest within the Cerrado–Caatinga ecotone in northeastern Brazil. This ecotonal region is characterised by strong contrasts in canopy cover, leaf litter accumulation and microclimatic variability, particularly in humidity and temperature. We sampled lizards using 50 pitfall‐trap arrays with drift fences distributed along four transects spanning the structural gradient. At each site, we quantified canopy cover, leaf litter weight and ground structure, and estimated microclimatic gradients from temperature and relative humidity data recorded with data loggers distributed across the trap network. We characterised environmental gradients using multivariate ordination, and evaluated relationships between environmental predictors and lizard assemblage structure using generalised linear models, generalised additive mixed models and generalised dissimilarity modelling. We captured 770 individuals representing 15 species, including generalist, ground‐dwelling and forest‐associated taxa. Lizard abundance was higher in open habitats and strongly associated with variability in relative humidity, suggesting that microclimatic fluctuations enhance fine‐scale habitat heterogeneity. Species richness did not vary significantly along the gradient, although forested sites supported additional habitat specialists. Species turnover was primarily associated with estimated relative humidity variability, minimum temperature, canopy cover and leaf litter weight, whereas geographic distance contributed minimally. These findings indicate that microclimatic variability and habitat structure act as dominant environmental filters shaping ectotherm assemblages at local scales in transitional landscapes, highlighting the ecological importance of fine‐scale environmental heterogeneity in Neotropical ecotones.