Weather of Arabia - The size of the birds in the Americas has changed to become smaller and longer-winged as global temperatures rise, which in turn affects smaller species faster. This is the result of a new study conducted at the University of Michigan and published in the Proceedings of the National Academy of Sciences of the United States of America.
The study combines data from two previous papers containing information on changes in body size and wing length of a sample of more than 86,000 birds over four decades in the Americas.
One study included information on migratory birds killed by collisions with buildings in Chicago, and another included non-migratory birds caught in the Amazon.
Although there are differences in species composition and geographic locations between the two sets of data, and despite the data being collected independently and using different methods, the birds in both studies showed a balanced shrinkage in body size and a balanced increase in wing length.
A new analysis of the collected data revealed an impressive pattern. He showed that the smallest species of birds shrink relatively more quickly in body size and increase relatively more quickly in wing length.
The Chicago and Amazon studies attribute a decrease in the body size of bird species to rising temperatures over the past 40 years. The study indicates that body size is an important factor in species response to climate change. However, the exact reason why smaller species respond to changes so quickly remains unknown.
This may be because smaller species experience greater evolutionary pressures. However, the research team doesn't know enough to know whether the observed changes in body size represent rapid evolutionary changes in response to natural selection.
If natural selection plays a role in the patterns we see, then the results indicate that smaller species are evolving at a faster rate because of their stronger response to evolutionary changes or their increased response to selection.
Based on the study, if temperatures continue to rise in the coming decades, larger birds are expected to respond more slowly to global changes. According to Marketa Zenova, an author of the study, this means that species with large bodies may be at greater risk of extinction, given their limited ability to adapt to the rapid and continuous changes caused by human activity.
On the other hand, the influence of body size on evolutionary rates may increase the persistence of taxa if rapid changes in size reflect a rapid adaptive response to changing conditions.
Data for 129 bird species were analyzed in this study, including 52 species of migratory birds that breed in North America, and 77 species of birds living in South America. Approximately 86,131 samples were collected in the same period using different techniques.
The comprehensive data set provided a unique opportunity for researchers to reveal whether or not key features of organisms such as body size and generation length would contribute to birds' response to rapid environmental changes.
According to biologists, the length of a generation, which indicates the average lifespan of individuals capable of reproducing, is an important indicator of a species' ability to adapt to rapid environmental change.
Organisms with short lifespans and rapid reproduction, such as mice, are expected to evolve faster than organisms with longer generations, such as elephants. This happens because mice have more chances to benefit from random genetic mutations that occur during reproduction.
In the new PNAS study, the researchers used statistical models to test the importance of length of generation and body size. After adjusting the results for body size, no relationship was found between generation length and rates of change in North American bird species. Generation time data were not provided for South American birds and were therefore not included in this part of the analysis.
At the same time, the new analysis showed that the species' average body size was closely related to the rates of change recorded for both Chicago and Amazon birds.
Body size can be an important indicator of adaptive capacity and ability to reduce extinction risk among species with contemporary evolution.
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