Non-native salmonids affect amphibian occupancy at multiple spatial scales

Pilliod, David; Hossack, Blake; Bahls, Peter; Bull, Evelyn; Corn, Paul; Hokit, Grant; Maxell, Bryce; Munger, James; Wyrick, Aimee

Brief Description: Investigating the effect of non-native salmonids on the occupancy of two amphibians (Ambystoma macrodactylum & Rana luteiventris) across different spatial scales. Aim: The introduction of non-native species into aquatic environments has beenlinked with local extinctions and altered distributions of native species.We investigated the effect of non-native salmonids on the occupancy of twonative amphibians, the long-toed salamander (Ambystoma macrodactylum) andColumbia spotted frog (Rana luteiventris), across three spatial scales: water bodies,small catchments and large catchments.Location Mountain lakes at ‡ 1500 m elevation were surveyed across thenorthern Rocky Mountains, USA.Methods We surveyed 2267 water bodies for amphibian occupancy (based onevidence of reproduction) and fish presence between 1986 and 2002 and modelledthe probability of amphibian occupancy at each spatial scale in relation to habitatavailability and quality and fish presence.Results After accounting for habitat features, we estimated thatA. macrodactylum was 2.3 times more likely to breed in fishless water bodiesthan in water bodies with fish. Ambystoma macrodactylum also was more likely tooccupy small catchments where none of the water bodies contained fish than incatchments where at least one water body contained fish. However, theprobability of salamander occupancy in small catchments was also influencedby habitat availability (i.e. the number of water bodies within a catchment) andsuitability of remaining fishless water bodies. We found no relationship betweenfish presence and salamander occupancy at the large-catchment scale, probablybecause of increased habitat availability. In contrast to A. macrodactylum, wefound no relationship between fish presence and R. luteiventris occupancy at anyscale.Main conclusions Our results suggest that the negative effects of non-nativesalmonids can extend beyond the boundaries of individual water bodies andincrease A. macrodactylum extinction risk at landscape scales. We suspect thatniche overlap between non-native fish and A. macrodactylum at higher elevationsin the northern Rocky Mountains may lead to extinction in catchments withlimited suitable habitat.

Non-native salmonids affect amphibian occupancy at multiple spatial scales

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