Amphibian Diversity of the Colorado Canyonlands including Potential Threats from Non-native Bullfrogs and Disease

Abstract/Summary

Ephemeral streams (hereafter, creeks) along the sandstone canyons of the Colorado and Uncompahgre Plateau provide habitat and breeding sites for native amphibians, although little is known about the diversity and distribution of amphibians that live in these harsh, dynamic environments. In addition, rivers that border these canyon tributaries serve as corridors for non-native species and disease. The American bullfrog (Lithobates catesbeianus) is a non-native species in western Colorado known to prey on native amphibians and act as a reservoir for pathogens such as Batrachochytrium dendrobatidis (Bd). From 2019-2022, we surveyed for amphibians using visual encounter surveys (VES) and eDNA surveys throughout the McInnis Canyon National Conservation Area (MCNCA), the Dominguez-Escalante National Conservation Area, and the Dolores River Canyon Wildlife Study Area. Our primary goals were to document the diversity and distribution of native amphibians in the canyonlands and evaluate possible threats to these species from bullfrogs and Bd. We found direct (VES) and indirect (eDNA) evidence that sensitive species, such as the Great Basin spadefoot (Spea intermontana) and the Northern leopard frog (Lithobates pipiens), inhabit these protected canyons. Most of the ephemeral tributaries did not support bullfrog populations, although we often detected them where the tributaries joined the rivers. In Mee Canyon (MCNCA), however, bullfrogs appear to migrate upstream into the canyon tributary in some years. A bullfrog individual also tested positive for Bd from Mee Canyon in 2019 and diet contents indicated that bullfrogs prey on native amphibians in this system. While non-native predators and disease are a concern for these ephemeral desert tributaries, they are likely minor relative to other threats such as drought and hydrological changes associated with ongoing climate change.