Diet analysis of adult Boreal Chorus Frogs (Pseudacris maculata) and Plains Spadefoot Toads (Spea bombifrons) during the breeding season

Abstract

Amphibians play roles in Canadian prairie ecosystems, contributing to food web dynamics. Despite their ecological importance, the dietary interactions of prairie amphibians remain understudied, creating a knowledge gap. Prairie amphibians face a unique suite of threats, including habitat loss, agricultural intensification, and climate change. Knowledge of their basic ecology is outdated, limiting effective conservation in agricultural landscapes. This thesis provides an update on the dietary ecology and morphology of the Boreal Chorus Frog (Pseudacris maculata) and the Plains Spadefoot (Spea bombifrons) in southern Alberta. Stomach contents from breeding adults (n = 50) were analyzed using the Index of Relative Importance (IRI), volumetric estimation, and inferential models. Results characterize Boreal Chorus Frogs as a resilient terrestrial generalist; while Coleoptera and Diptera were the numerically dominant, Lepidoptera contributed the majority (62.1%) of dietary volume. Diet composition was significantly influenced by local habitat and constrained by predator morphology; gape width limited maximum prey size, and gravid females consumed significantly fewer prey items than non-gravid females, indicating a reproductive trade-off. Breeding male S. bombifrons exhibited a complete fasting during calling, consistent with an “explosive” breeding strategy. These findings support holistic wetland and upland management by demonstrating that P. maculata relies on terrestrial prey for 73% of its energy. This dependence underscores the need for protected upland buffers. The consumption of crop pests also identifies a potential “ecological trap,” where terrestrial foraging may increase exposure to agrochemicals. This research establishes a modern baseline for amphibian conservation in Alberta.