 Abstract | This thesis discusses the current field of evolutionary biology and examines patterns and processes of divergence in the morphology and behaviour of a key model species, the New Holland Honeyeater (Phylidonyris novaehollandiae). More specifically, the cause of phenotypic divergence between island and mainland populations, and populations exposed to different climatic conditions, is investigated in P. novaehollandiae. Island-mainland comparisons showed that island birds were larger than mainland birds in tarsus (2.5%) and bill length (3.7%), had a wider foraging niche (mostly due to greater insect consumption), and foraged more from the bark and air (sallying). Island birds also had longer foraging times than mainland birds, which may be evidence for reduced resource availability. This evidence, and evidence from the literature, suggests that a paucity of resources on Kangaroo Island has most likely driven niche expansion, facilitated by the absence of some bird species on the island. Larger body size in island birds appears to be a response to local conditions on the island and may be driven by natural selection or population-scale phenotypic plasticity. Comparisons across a climatic cline showed that variation in all morphological traits in males and two of four morphological traits in females correlated with variation in rainfall. Additive genetic variation exceeded that of neutral genetic variation for all morphologic traits, indicating a strong signal of selection -- the observed environmental correlation suggests an environmental driver. These observations are consistent with the hypothesis that, in drier climates in South Australia, reduced and unpredictable nectar availability drives natural selection for increased aerial insect foraging (and maybe dispersal) efficiency. The lack of correlation found for some female traits was most likely explained by female biased-dispersal weakening the signal of the selective source. The findings of this research add to a body of research that aims to understand and predict the evolutionary response of organisms under a changing climate. |
