Spatial variation in the diet of Buller’s Spiny Lizard Sceloporus bulleri from Western Mexico

Dietary variation across elevational gradients offers insight into how prey availability shapes foraging strategies. We examined stomach contents of Sceloporus bulleri , a viviparous lizard endemic to the Sierra Madre Occidental, across four populations spanning a broad elevational range on the Pacific slope of Jalisco, Mexico. Following the niche variation hypothesis, we predicted that higher-elevation populations, where arthropod diversity is typically reduced, would show narrower individual niches and lower among-individual dietary variation than lower-elevation populations. We identified 47 prey types, dominated by hymenopterans, hemipterans, and arachnids. Contrary to expectations, prey richness, mean prey items per stomach, prey-group diversity, and individual specialization (WIC/TNW ratio, trophic niche breadth) did not differ significantly among populations. However, individual-level analysis using the Proportional Similarity Index showed that populations with lower mean specialization values (Las Juntas y Los Veranos and San Sebastián del Oeste) contained proportionally more dietary specialists. Populations also differed significantly in prey hardness and evasiveness, with Talpa de Allende and Mascota showing distinct prey-texture preferences, and Las Juntas y Los Veranos and San Sebastián del Oeste differing in reliance on evasive prey. These results suggest that population-level niche breadth remains stable across elevation in S. bulleri , while individual specialization and prey-trait selection vary independently of elevation.