A global assessment of alien amphibian impacts in a formal framework

Abstract

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.

Impact assessment with different scoring tools: How well do alien amphibian assessments match?

“…A full reference list can be found in Measey et al (2016). We found that both EICAT and GISS maximum score were not related to the number of publications found on the species' impacts (Kendall's tau = 0.24 and 0.25; P = 0.059 and 0.055 respectively; Figure 2).…”

“…The formulation in GISS of a maximum disease impact (see Nentwig et al 2016) leaves room for different assessors to score different impacts, based on their interpretation, which might have led to a high score in GISS and a MO in EICAT. Given the severity of the effects of Batrachochytrium dendrobatidis and other diseases, both EICAT and GISS appear to highlight the difficulty of assigning the spread of disease through alien taxa and the transmission thereof to native species (see also Measey et al 2016, Evans et al 2016, although this is widely acknowledged in amphibians (Fisher and Garner 2007).…”

“…They comprised of a list provided by Kraus (2009) and additional searches for species with introduced distributions indicated in the IUCN Red List, and led to a selection of 105 alien amphibians (see Measey et al 2016 for details).…”

“…Here we only use scores that relate to environmental assessments of both schemes, because economic assessments were poorly populated for amphibians (see Measey et al 2016) and it was necessary to keep the results comparable between the two schemes.…”

“…For this study we were interested in whether two impact scoring systems relying on published evidence, rather than expert opinion, would lead to the same classification of alien species, using amphibians as a case study. Alien amphibians are an interesting group as the total number of introduced species is relatively small and they can be assessed in their entirety (Kraus 2009), and the quantity and quality of literature reflects that of other taxa (Measey et al 2016, Evans et al 2016.…”