Assessing the extinction risks of amphibians impacted by infectious diseases

Emerging infectious diseases (EIDs) are a major threat to amphibians worldwide. Determining the extinction risk of species susceptible to EIDs is challenging because of data limitations, especially in the initial stages of emergence and spread of disease. The fast rate of spread of many EIDs makes it necessary to assess the extinction risk of impacted host species before detailed mechanistic (epidemiological) or correlative (ecological niche) models can be developed. We present a simple method for identifying species that are at the highest risk of extinction due to an EID. Our method incorporates projections of the spatial spread of disease into IUCN Red List assessments under criteria A3 (based on future population reductions), D2 (plausible future threats), and E (probability of extinction). We apply this method to assess the extinction risk of salamander species in Europe susceptible to population declines caused by Batrachochytrium salamandrivorans (Bsal), the agent of the salamander plague. Our results indicate a high risk of extinction for European salamanders as a result of the spreading Bsal infection. Depending on the rate of spread from the current Bsal localities, and the emergence of new localities through human travel and transport, the number of species threatened by Bsal can range from a few to almost 30 of the 40 species that occur in Europe. Our method allows preliminary assessments of extinction risk based on limited information. For species at risk of extinction due to fast-spreading EIDs, it provides a pragmatic and precautionary solution until more realistic models can be developed.