Rethinking niche conservatism with phylogenetic location-scale models

Phylogenetic niche conservatism (PNC) describes the tendency of evolutionary lineages to retain functional traits over time, leading to closely related species exhibiting similar phenotypes and ecological niches. Traditional approaches to studying PNC focus on phylogenetic signal in trait means, often overlooking the conservation of trait variability across lineages. This oversight limits our understanding of the ecological constraints on species adaptation. Trait variance, influenced by genetic, ecological, and environmental factors, is crucial for understanding evolutionary processes and species adaptive potential. Phylogenetic location-scale models offer a promising framework to incorporate both mean and variance components of trait evolution, providing a more nuanced understanding of how ecological and evolutionary processes shape trait evolution across lineages. We apply this approach to leaf economic data for the genus Eucalyptus, demonstrating that models including predictors for both mean and variance offer greater predictive performance and deeper insights into the mechanisms of niche conservatism and ecological adaptation. Our findings highlight the importance of considering trait variance in studies of PNC and its implications for assessing species resilience to environmental change.