Bioclimatic modelling, morphology, and behaviour reveal alternative mechanisms regulating the distributions of two parapatric salamander species

Question: What ecological and evolutionary processes are important in maintaining parapatric distributions of sibling species? Hypotheses: Previous research has suggested that competition is a likely factor limiting species distributions and maintaining parapatric distributions. Alternatively, abiotic restrictions such as climatic factors and local adaptation can also limit species’ ranges. Organisms: Plethodon hubrichti, a mountaintop endemic salamander, has an extremely limited geographic range that is entirely surrounded by the widespread Plethodon cinereus. Previous studies have suggested that P. hubrichti may be geographically restricted as a result of interspecific competition with P. cinereus. Methods: We studied the relationship between trophic morphology and diet in allopatric and sympatric populations to examine the effect of exploitative competition on geographic distribution. Behavioural experiments were conducted in the laboratory to determine the effects of interference competition. We complemented these analyses with bioclimatic modelling of species’ ranges and climate–phenotype correlations to examine the abiotic impact. Results: Our results suggest that aggressive interactions with P. hubrichti restrict the distribution of P. cinereus and not the converse, whereas P. hubrichti appears to be limited by abiotic climatic factors