Idade evolutiva e probabilidade de extinção

Abstract

Resolving whether species age is associated with extinction probability can help us understand the extinction dynamics of living and extinct clades. This pattern is called Age-dependent extinction (ADE), and there is no theoretical nor empirical consensus about its direction. In this thesis, as the first chapter, we propose the Clade Replacement Theory (CRT) as a framework that considers clades' evolutionary and ecological aspects for generating testable predictions on ADE patterns. During the ADE study, we realized a conceptual difference in species age definition between paleontology and neontology. Besides, because the branch lengths of phylogenies estimate it, the latter has substantial uncertainty sources. Therefore, in the second chapter, we evaluated the error rates of phylogenetic ages associated with speciation modes and different extinction scenarios through simulations. Complementarily, we proposed an approach to correct age estimates under the assumption of bifurcating speciation. We formalized CRT with two propositions. The first one is incumbency effects by the old clade over the niche space, limiting the diversification and dominance of new clades. Due to the colonization and subsequent rapid diversification of the old clade, we hypothesize that this niche occupation trajectory would generate a pattern of older species occupying central niche positions. In the third chapter, we explore this hypothesis in the context of Neotropical tetrapods. We found no generality in the relationship between species age and niche position for these groups. However, the relationships that were significant supported our expectations. The CRT's second proposition is an ecological shift that would select against the old clade, opening up an opportunity for the new clade to diversify and rise to dominance. From CRT's propositions, we developed the prediction that the ADE scenario would be defined by whether an ecological shift happens or not. If it does not happen, we expect a negative ADE; i.e., older species would be less extinction prone. On the other hand, if it does happen, we expect a positive ADE; i.e., younger species would be less extinction prone.