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As bird skeletons become more complex they lose diversity

Scientists have identified a striking correlation between the complexity of bird skeletons and the overall diversity within the bird kingdom. It demonstrates a unique understanding of the evolutionary spectrum of birds, showing that as birds become more advanced and specialized in their ecological niches, they display a decrease in species diversity.

Studying bird complexity

The in-depth study involved the meticulous examination of 983 species spanning all prevalent groups of extant birds. The team, aiming to explore the intricacies of avian evolution, measured skeletal complexity by analyzing the variance in bone structure between the wings (forelimbs) and legs (hind limbs) of the birds.

Researchers discovered that birds possessing less complicated skeletons, evidenced by minimal differences between their fore and hind limbs, boasted a higher species diversity. Examples of such birds include pigeons, gulls, and songbirds (passerines), which, despite their skeletal simplicity, inhabit diverse ecological settings globally, showcasing extensive species richness.

Complexity leads to specialization

Conversely, species like flamingos and ostriches exhibit more complex skeletal structures. In particular, they have shorter wings compared to their legs, which renders them more specialized for their habitats.

This specialization implies that birds with intricate skeletons are often confined to specific niches and exhibit decreased versatility in subdividing those niches to generate new species.

Professor Matthew Wills, from the Milner Centre for Evolution, elucidates, “Our study reveals that birds tend to be less likely to diversify into new species as they become more specialized. It’s a fascinating insight into how specialization can impact the ability of organisms to evolve and adapt.”

Evolutionary implications

While evolution can certainly generate forms with lower complexity, birds with sophisticated skeletons have seemingly developed more entrenched specializations over time. This specialization potentially hinders their ability to revert to simpler forms.

Andrew Brinkworth is a PhD student at the University of Bath and the leading author of the study. He asserts that such specialized species, due to their reduced evolutionary paths and heightened ecological specificity, are potentially more vulnerable to environmental shifts. These include habitat degradation, disruptions in food chains, and climate variations.

Ecological specialization and extinction risk

Birds with advanced skeletons not only exemplify ecological specialization but also inhabit fewer habitats and exhibit restricted foraging behaviors. This heightened specialization and the resultant decrease in diversity may escalate their susceptibility to extinction amidst environmental alterations.

Brinkworth further warns, “Our findings predict a heightened extinction risk for birds with more intricate skeletons and less diversity due to their lack of adaptability to environmental changes.”

More research needed

This revelatory study, a collaboration between the University of Bath, University of Lincoln, University College London, and the Chinese Academy of Sciences, is a stepping stone in the ongoing pursuit to unravel the secrets of evolution and biodiversity. The next phase of research aims to discern whether similar patterns of complexity and specialization affecting diversity are observable in other animal kingdoms as well.

Funded by the NERC GW4+ Doctoral Training Partnership, John Templeton Foundation, and BBSRC, this research not only broadens our understanding of avian evolution but also propels forward the discourse on biodiversity, adaptation, and the ongoing struggle against extinction in the face of rapid environmental changes.

The full study is published in Nature Communications by the Milner Centre for Evolution at the University of Bath.

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