Ecological niche similarity between congeneric Mexican plant species

Background and aims - Ecological niche conservatism describes the tendency of phylogenetically related species to maintain the characteristics of their ancestral fundamental niches. Our aim was to assess niche conservatism of species belonging to two plant genera of the Family Asteraceae endemic to Mexico: Dyscritothamnus includes two woody species restricted to the dry scrublands of central Mexico and Loxothysanus includes two herbaceous species distributed mostly in temperate environments from central Mexico southward. Methods - Using geographical distribution data of species obtained from critically reviewed herbarium specimens (45 of Dyscritothamnus and 94 of Loxothysanus), niche models were obtained using the Maxent program. The climatic variables evaluated were chosen using principal component analysis. Subsequently, with the program ENMTools we quantified the degree of overlap and similarity between the niches of congeneric species using the equivalence (D) and similarity (I) parameters. Key results - The two species of Dyscritothamnus are sympatric, influenced by common environmental features; accordingly, their niches show high equivalence values (D= 0.563), suggesting niche conservatism. On the other hand, the genus Loxothysanus shows a wider geographical distribution; their species niches are not equivalent (D = 0.145) and have a relatively low value of environmental similarity. Conclusion - The distributions of the species of Dyscritothamnus support the hypothesis of niche conservatism because of their sisterhood and quite similar distribution patterns that result in high niche conservatism values. In contrast, species of Loxothysanus do not support clearly such a hypothesis, suggesting their niches have suffered adaptive changes to contrasting environments.