Microhabitat use within a contact zone of parapatric land salamanders in the Swiss Alps

Studies investigating the contact zones in parapatric species can provide valuable insights into the mechanisms that cause range borders. Such studies can also provide a better understanding of the mechanisms which allow coexistence within contact zones. In land salamanders, parapatric range limits among species are often determined by abiotic factors and interspecific competition. The ranges of the parapatric Salamandra salamandra and S. atra narrowly overlap in the European Alps. Climatic gradients that determine their parapatric range margins suggest dissimilar species-habitat-relationships. However, habitat use for these species has not yet been studied in the contact zone where the parapatric ranges overlap and where the species locally co-occur in syntopy. To better understand their parapatric range limits and local syntopy, we compared the species’ microhabitat use in a contact zone in Switzerland and quantified the degree of interspecific niche overlap in relation to resource availability. We observed that most studied microhabitat variables were neither selected nor avoided by the two species, suggesting random use of the habitat for the variables that we studied. Interspecific niche overlap was generally large, but did not differ from that expected by chance. Unlike previous studies that analyzed patterns of co-occurrence of these species at larger spatial scales, we observed no niche differentiation within the contact zone. Both species likely select the same areas that are suitable and available for salamanders while they similarly avoid generally unsuitable habitat. This indicates that niche differentiation can vary depending on the spatial scale where it is investigated