A global assessment of alien amphibian impacts in a formal framework

Aims The environmental and socio-economic impacts of alien species need to be quantified in a way that makes impacts comparable. This allows managers to prioritize their control or removal based on impact scores that can be easily interpreted. Here we aim to score impacts of all known alien amphibians, compare them to other taxonomic groups and determine the magnitude of their ecological and socio-economic impacts and how these scores relate to key traits. Location Global. Methods We used the generic impact scoring system (GISS) to assess impacts. These impacts were compared to other previously assessed taxonomic groups (mammals, birds, freshwater fish, invertebrates and plants). For each species scored, we investigated the relationship of impacts with key variables (taxonomy, size, clutch size, habitat and native range) using general linear mixed models. Results Our data show that alien amphibians have similar impacts to other taxonomic groups, but comparatively fewer (41%) could be scored using available literature: < 7% of species had 71% of literature used for scoring. Concerning the environment, amphibians scored similar to birds and fish, but lower than mammals. Regarding socio-economy, only seven species scored impacts, but these were surprisingly serious. Bufonids and pipids consistently scored higher than other amphibian taxa. Species with larger body size and more offspring had higher environmental impacts. Main conclusions Alien amphibians appear to be comparable to other taxa such as birds and freshwater fish in their environmental and socio-economic impact magnitude. However, there is insufficient literature to score impacts of the majority of alien amphibians, with socio-economic impacts particularly poorly represented.