Age‐related trends in niche position and specialization in Neotropical vertebrates

Species' niche positions and breadths within a region's environmental space, measured through ecological niche factor analysis (ENFA) as marginality and specialization, can reflect evolutionary constraints related to lineage age. The ‘internal incumbency' hypothesis predicts that older species, due to competitive preemption, occupy more central niche positions than younger ones. In addition, regarding specialization, there are two contrasting predictions: the ‘time‐and‐specialization' hypothesis posits that older species are more specialized given that they had more time to adapt to an environment, whereas the ‘resource‐use' hypothesis proposes that younger species are more specialized due to occupying narrower ecological niches, which may drive higher speciation and extinction rates. This study explores the relationship between species age and their climatic niche position and specialization among Neotropical terrestrial vertebrates. Using ENFA, we estimated the marginality (niche position) and specialization (niche breadth) of 1175 mammals, 3001 birds, 1826 reptiles and 1435 amphibians across the Neotropical biomes occupied by each species. Phylogenetic generalized least squares (PGLS) models were used to analyze the relationships between species age, marginality, and specialization across vertebrate classes. Although regression coefficients were predominantly negative, suggesting that older species tend to occupy more central niche positions and exhibit lower specialization, the explanatory power of the models was extremely low. Taken together, the consistently negligible variance explained across taxa and biomes indicates that species age is not a general driver of niche position and specialization, contrary to the expectations articulated in our hypotheses.