| Summary: | Coloration fulfils a variety of adaptive functions in animals. Colour variability, both between and within species, can be caused by different colours being favoured for different functions and in different environments. Thus, species with highly variable coloration may have greater potential to persist in new and changing environments. As a consequence such colour variable species may be more able to adapt, colonize new areas and niches, occupy larger ranges, speciate more readily and in general be less vulnerable to environmental change and extinction. These predictions have been supported by comparative analyses on amphibians and reptiles. However, since coloration in ectotherms plays a key role in thermoregulation, it is unclear whether these results can be generalised to endotherms, such as birds and mammals. Here we test the hypothesis that more colour variable endotherms occupy larger ranges/niches and are less vulnerable to the threat of extinction by focusing on colour variation in Australian parrots and passerine birds. As predicted, colour variability was correlated with range size (parrots and passerines) and niche breadth (dietary heterogeneity, parrots only). These relationships support the predicted link between colour variability and adaptability, whereby range size and niche breadth may be a cause of colour variability or vice versa. Irrespective, and as predicted, colour variability was lower in threatened species, even after statistically controlling for other confounding variables. Hence our study supports the hypothesis that colour variable species in general are more resilient to environmental change. Passerines: Colour variability and associated variablesVariable names (see Methods for more details) Data collated from the Handbook of Australian, New Zealand and Antarctic Birds vols. 5-7 animal: species code used in the phylogeny av.col.var: average colour variability (sexes pooled) m.col.var: average colour variability (males) f.col.var: average colour variability (females) polymorphic: ...
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