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The rainbow trout is affecting the occupancy of native amphibians in Patagonia

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In this work, we assessed the occupancy of two native amphibian species of the Valcheta stream in the Somuncura Plateau, northern Patagonia: the Valcheta frog, Pleurodema somuncurense and the Argentine common toad, Rhinella arenarum. We hypothesized that the occupancy of both amphibian species will be shaped by the presence of trout; we also expected a decline in occupancy assuming that the new predator in the system will affect native amphibian populations. Between December 2014 and March 2015, we conducted surveys in 148 sites along the headwaters of Valcheta stream. We modelled the occupancy by including the presence of trout, the temperature of water and the coverage of rocks and vegetation as site-habitat covariates. Models including trout were among the best ranked for both amphibian species. The presence of trout reduced the occupancy of both species and the magnitude of this reduction was much higher in the Valcheta frog than in the Argentine common toad. Overall, our results are of great relevance for land managers considering that the Valcheta frog is among the only three IUCN Critically Endangered amphibians in Argentina.

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We would like to thank park-rangers (Ariel Lapa; Valeria Pazos; Mariela Guzmán and Gerardo Melivilo) and volunteers (Joaquín Carrera; Mauricio Akmentins; Camila Kass; Facundo Bossa; Marcos Waldbillig and María Luz Arellano) for their kind assistance during the fieldwork. Jorge Williams made valuable suggestions for improving this manuscript. The Secretaría de Ambiente y Desarrollo Sustentable de Río Negro gave us necessary permits to perform this work. This study was supported by Mohamed Bin Zayed Species Conservation Fund; PIP-11220150100598CO-Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and F14AP00749-Wildlife Without Borders - Amphibians in Decline (USFWS).

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Correspondence to M. A. Velasco.

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Guest editors: John E. Havel, Sidinei M. Thomaz, Lee B. Kats, Katya E. Kovalenko & Luciano N. Santos / Aquatic Invasive Species II

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Velasco, M.A., Berkunsky, I., Simoy, M.V. et al. The rainbow trout is affecting the occupancy of native amphibians in Patagonia. Hydrobiologia 817, 447–455 (2018).

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