The diet of the eastern short-horned lizard (Phrynosoma douglassi brevirostre) in Alberta and its relationship to sexual size dimorphism

The diet of Phrynosoma douglassi brevirostre in Alberta was investigated and potential prey abundance was examined. The Alberta populations are less strongly myrmecophagous than the average for the species, when the diet is broken down by prey item counts. Breakdown of the diet by prey dry weight shows that ants, nonsilphid Coleoptera, and Orthoptera are the major components of the diet. The range of prey sizes taken is large, but the species concentrates on a small range of prey sizes, from 2.1 to 6.0 mm in length. Arthropod abundances are significantly different between all three study sites, and there is always a significant difference in distribution between the pooled pitfall samples and the pooled gut samples of any one study site. The general dissimilarity in distribution between the pooled gut samples of any two study sites suggests some dietary flexibility. The size range of prey items taken by the large lizards includes and slightly exceeds the size range of prey items taken by medium-sized lizards, and there is a significant positive correlation of average prey size with lizard snout–vent length. There are significant differences in the prey sizes, prey dry weights, and prey item counts between large lizards and medium-sized lizards, indicating intersexual dietary partitioning.