Accelerated Amphibian Extinction Rates and the Influence of Hybridization

A biodiversity crisis is currently unfolding in which large proportions of Earth’s species are declining in populations or are at risk of extinction. Amphibians are one of the hardest hit groups, with over 40% of all amphibian species at risk of extinction. Addressing this biodiversity crisis requires identifying both which groups are most at risk for extinction and what factors contribute to extinction risk. Hybridization, defined as the interbreeding of genetically distinct species, is one factor that has the potential to alter species’ extinction risk by reducing offspring fitness or introducing beneficial new genotypes. However, little is known of how hybridization impacts extinction risk, especially in amphibians. We addressed these issues by 1) calculating extinction rates for different amphibian groups and 2) identifying whether hybridization was associated with extinction risk across amphibian species. To do so, we used IUCN data. We calculated current extinction rates within amphibians and contrasted these rates with highly conservative rates of background extinction. We also determined potential to hybridize using measures of range overlap and information from published literature. We combined this data with data for habitat and elevation for amphibian species and asked if this was associated with IUCN status. Additionally, we mapped species’ distributions and assessed trends within high density areas to review species’ geographic relationship with hybridization. Calculations of modern extinction rates were found to be much higher than previous background rates in almost all amphibian subcategories, and analyses of preliminary data among IUCN categories indicate a statistically significant relationship between engaging in hybridization and a reduced threat of extinction. Our findings emphasize that, to better conserve amphibians, further investigations into risk factors for extinction, such as hybridization, are needed to form a more holistic view of the threats faced by these vulnerable species.