Loss of habitat suitability and distribution range of the endangered Japanese giant salamander under climate change

Giant salamanders are the world’s largest amphibians and keystone predators in riverine ecosystems where they face global declines. Identifying environmental variables influencing their distribution is, therefore, an essential step for their conservation. This study aims to assess the current habitat suitability and distribution of the Japanese giant salamander (Andrias japonicus) and to predict changes under future climate scenarios. We used species distribution models (SDMs) over a 282,916 km² area, including 477 high-resolution occurrence data of giant salamanders and seven remote-sensing environmental predictors (climatic, topographic and land use). We projected the prediction maps, identified the most contributing variables and calculated the shifts of suitable areas for three periods (2050, 2070 and 2090) under projected climatic conditions. Climatic variables highly contributed to the distribution of giant salamanders (76% of the total), with preferences for areas with moderate precipitations during cold and wet seasons and mild summer temperatures. A moderately steep surrounding environment was favourable for salamanders, whereas the land-use variables had less influence. Future climate predictions indicate a major decrease of suitable areas. Altogether, our results highlight the habitat preferences of giant salamanders at a broad scale and the negative impact of climate change on future suitable areas. These findings provide important steps for upcoming conservation actions for this threatened species in delineating favourable distribution ranges and priority areas that should be directly affected by climate change. Finally, they emphasise the need for new research at a fine scale on disturbances to the aquatic habitat to enhance the conservation of giant salamanders.

We used a species distribution model (MaxEnt), high-resolution occurrence data and remote sensing data (climatic, topographic and land use) to identify suitable habitats for the Japanese giant salamander in Japan.

The most suitable environments for the Japanese giant salamander are located both within and beyond its current distribution range, with the ‘Japanese Alps’ forming an impassable natural barrier.

Among the variables studied, precipitation of the warmest quarter, precipitation of the coldest quarter, mean temperature of the warmest quarter and mean temperature of the wettest quarter were the most important environmental predictors of the species’ distribution.

Climate change is expected to severely reduce the potential suitable geographical areas for the Japanese giant salamander in the future.

The present work calls for new surveys based on the projected maps to improve the mapping of salamander distribution and to focus on ecological features and threats at the aquatic habitat level to understand the risks to their populations.