The Toad & the Crayfish: Arizona Toad & Non-native Species Occupancy & Interactions in Streams of Arizona

Authors: Brett Montgomery, Heather Bateman

Year: 2022

Abstract

The Arizona Toad (Anaxyrus microscaphus) is a unique southwestern toad because they primarily breed in streams of Arizona, New Mexico, Utah, and Nevada. Arizona Toad is a species of conservation concern throughout their range due to hybridization, flow regime changes, and habitat loss. Invasive aquatic species, such as crayfish, are suspected to impact Arizona Toads, but this risk has not been evaluated. The non-native Northern Crayfish (Orconectes virilis), which co-occurs with the toad in the Mogollon Rim, are opportunistic omnivores implicated in the declines of other native aquatic species. We used visual encounter toad survey data from 2021 and 2022, and crayfish occurrence records, to determine if there are any interactions between the two species. We applied three occupancy modeling approaches, single-species, two-species, and species interaction models, focused on streams throughout the range of the Arizona toad in Arizona. Using our first season of data, we found Arizona Toad site occupancy probability was 0.165 (SE = 0.03) and detection probability when present was 0.734 (SE = 0.06) with the single-species models. The top two-species occupancy model showed toad site occupancy probability in the presence of Northern Crayfish was 1.0 (SE < 0.01), with the species interaction factor of 1.0 (SE = 0), indicating species independence. During the second season, Arizona Toad site occupancy probability was 0.221 (SE = 0.057) and detection probability when present was 0.841 (SE = 0.087) in the single-species models. The top two-species occupancy model produced the same results as the first season, showing species independence. Overall, our single season results found low toad occupancy, but high detection, as well as significant overlap with crayfish. Understanding toad-crayfish co-occurrences and interactions in areas dominated by crayfish is critical for risk assessment and this work provides a framework to further address these issues.