Habitat Suitability Index is not relevant for great crested newt occupancy at its range margins: a Mediterranean case study

For effective conservation, robust tools that can measure and predict spatio-temporal population variation are required, especially for species in steep decline, rarely encountered or difficult to detect, such as many amphibian species. This study focused on the relevance of the Habitat Suitability Index (HSI) and its component variables to assess habitat and predict the presence of the great crested newt ( Triturus cristatus ) in the southern margin of its range. We monitored the species to test (1) the effectiveness of different methods for detecting newts, and (2) the influence of different landscape variables on its occupancy probability. Our results indicate that while eDNA is a highly effective detection tool, it is not sufficient on its own to detect all occupied ponds by the great crested newt, that HSI is not a good predictor of pond occupancy at the range margins of this species, and that the species’ presence is significantly and negatively influenced by the distance to the nearest positive pond and the HSI pond drying. Our findings suggest that the conservation of the species in the southern margins of its range can only be achieved by maintaining the terrestrial and aquatic connectivity of the different identified populations.