Multi-factorial analysis reveals positive intraspecific interactions in European plethodontid salamanders

Studying interactions between individuals in wild populations is essential to understanding intraspecific population dynamics and interspecific relationships with co-occurring species. One of the main challenges is considering the multiple confounding factors that can mask the specific trait you are looking for. To quantify the interactions between conspecific individuals, we need to consider the potential effects that both abiotic and biotic factors may have. In this study, we adopted this methodology to shed light on intraspecific interactions between Speleomantes cave salamanders, for which both positive and negative interactions have been described. We monitored multiple subterranean populations of the Italian cave salamander S. italicus monthly for a year, recording different abiotic and biotic parameters. Then, we analysed the density data of different groups (juveniles, adult males, and adult females) using Structural Equation Modelling. This approach discriminated the effects of microhabitat and potential prey and predator species on Speleomantes, allowing the detection of possible interactions between salamanders. Some of the considered abiotic and biotic factors had a limited (or no) effect on the abundance of Speleomantes. Conversely, we consistently found positive, strong correlations between the different Speleomantes groups. These results represent the first information related to the social interactions of wild Speleomantes populations, showing positive reciprocal covariation between individuals’ density. This data opposes the multiple information available from American plethodontid salamanders, creating an interesting case study. Our work highlighted the importance of considering the effects of multiple ecological factors to detect and qualitatively analyse intraspecific interactions properly.