The Evolution of form and function across taxonomic scales of passerines

Abstract

Adaptive radiations, the process by which organisms diversify both taxonomically and ecologically, have been attributed to underline the majority of living biodiversity. This type of evolutionary radiation typically transpires following the exploitation of vacant niche space though is not restricted to insular communities as numerous large clades likely diversified in much the same way. There is considerable variation in morphological and ecological diversity both within and between clades at all taxonomic scales. Several near-complete phylogenetic trees and datasets were used to investigate clade disparity in abstract space, trait evolution and the associations between morphology, ecology and diversification rates. These were combined to assess whether imbalances in speciation rates occur among taxa possessing particularly extreme morphologies in beak and body traits. New approaches capturing disparity metrics were used to quantitively analyse the hypervolumes of diverse families and smaller subclades within multidimensional space. These metrics were then employed to assess whether passerine families possess greater disparity in either their beak or body morphospaces. Thraupidae are an incredibly diverse passerine family with its various subclades exhibiting contrasting levels of taxonomic and morphological diversity. Analysis of these two evolutionary aspects revealed speciation rates are often decoupled from trait disparity among the various tanager subclades. Finally, the extreme disparity in form among the nested adaptive radiations within Thraupidae and other passerine families were explored to assess their contrasting trajectories with other endemic taxa to understand how such discrepancy in diversity was achieved and the factors that likely generated it.