Integrating fine-scale habitat suitability and hydrological structures to assess population connectivity for the Kaiser's mountain newt (Neurergus kaiseri) in southwest of Iran

Abstract

The unique life cycle of amphibians, encompassing both aquatic and terrestrial stages, poses challenges for examining landscape connectivity within meta-populations. Their heavy reliance on water and limited mobility exacerbate these challenges. Fine-scale investigations of environmental factors contribute to understanding the distribution range and landscape connectivity of amphibian meta-populations. The present study examines the habitat suitability and connectivity among population cores of the Luristan newt (Neurergus kaiseri), a vulnerable (VU) species in southwest Iran. Using the Digital Elevation Model (DEM) and hydrological tools, the boundary of the study area was defined based on drainage basins and Maximum Entropy (MaxEnt), incorporating eight habitat variables to investigate the distribution range. Given that amphibians rely on moisture to move, DEM was used to calculate the Sediment Transport Index (STI) as a surrogate for suitable movement contexts. Using this index, the potential movement of sediment within streams across the landscape will be assessed. A high STI value can limit amphibian movement and shelter and therefore threaten the survival of larvae. Here, the STI was fuzzified based on the presence points using the s-shaped method and the symmetric membership function. The fuzzy overlay technique was employed using the habitat suitability map and OR logic, and finally, the inverse of the fuzzy map was used as landscape resistance. Sub-basins with at least two population cores in the drainage basin were identified and their linkage was established using the Linkage Mapper. Also, the depth and number of sinks along the linkage path of the population cores in each sub-basin were identified. The MaxEnt analysis highlighted the variables of elevation, distance from streams, and proximity to the forest as the most important factors influencing N. kaiseri. All Iranian populations of N. kaiseri were located within a single drainage basin. In this drainage basin, there were five sub-basins with more than two populations. Sub-basin 4 encompassed the largest population and exhibited the highest connectivity quality (29 flow rate). The maximum depth of the links between the population cores in this sub-basin reached 100 m from the surface, and a large segment of the population was located in the upper part of the sub-basin. 432 sinks were located between the population cores that helped conserve water, create microclimates, and supply moisture.The arrangement of the populations within the sub-basin, along with the presence of sinks and variations in linkage path depths created distinct conditions for population cores. These conditions significantly influenced the quality of the linkages. The results of the present study can serve as a valuable tool to identify and prioritize population cores and sub-basins for targeted conservation efforts.