Joel Asaph Allen is one of the most famous bird watchers in American history, and even a brief review of his career helps illustrate why. The 19th century scientist traveled from Dakota Territory to Brazil to collect specimens. When his health made further expeditions impossible, he established himself as a leading researcher and writer, even helping to found the American Ornithologists’ Union (now part of the American Ornithological Society). He later became the first curator of birds and mammals at the American Museum of Natural History and ultimately the first head of its ornithology department.
He also discovered an important biological rule regarding homeothermic animals (formerly known as warm-blooded animals), a rule that is tragically becoming relevant as climate change alters the planet. Known as Allen’s Rule, she argues that, generally speaking, animals‘ appendages evolve to increase in size as the temperature around them increases as well.
According to a recent article published in the journal “Trends in Ecology & Evolution”, Allen’s rule is manifested in a number of animals due to climate change. In other words, the body of animals adapts and changes in response to heat.
As the study’s co-authors write, “There is widespread evidence of ‘shape change’ (changes in the size of appendages) in endotherms in response to climate change and associated warming.” This has been observed in animals ranging from the large round-leaved bat, which has seen its wings increase in size, to wood mice, whose ears have increased in length.
“Allen’s rule is about the size of the appendages – so we would expect the ears, tail, beak and legs to increase in size relative to the rest of the body as temperatures increase,” Sara Marie Karin Ryding, a faculty member at the Center for Integrative Ecology at Deakin University, told Salon via email. âSeeing that animals evolve according to Allen’s rule (and previous studies have shown that animals evolve according to Bergmann’s rule) also raises the possibility that animals evolve according to other biogeographic rules, such as Gloger’s Rule (animals in warmer conditions and more humid environments tend to be more strongly pigmented). “
Shannon Conradie, a PhD candidate in the Department of Zoology and Entomology at the University of Pretoria (and who did not contribute to the study), wrote to Salon that the study reinforces concern for scientists as to the future of our feathered friends.
“High temperatures and heat waves have been shown in numerous studies to lead to risks of dehydration and avoidance of hyperthermia,” explained Conradie. “Birds can lose up to 5% of their body mass through evaporative water loss within hours to prevent hyperthermia, but this can lead to fatal dehydration if temperatures remain high throughout the day.”
While Conradie finds it “amazing” that some birds can develop larger bills to compensate for the effects of radiative heat loss, she notes that “one of the main concerns here is when do the changes become more damaging than beneficial. There will probably be trade. and the consequences of the shape change and I think we still have a lot to discover about how these changes directly influence species. “
One concern, for example, is whether changing the size of the beak will affect evaporative heat loss when birds are in areas with a higher risk of fatal dehydration.
Ryding observed, when asked about some of the most striking changes the researchers noticed, that “the biggest that I think we’ve seen are Australian parrots, where species like gang cockatoos and red-rumped parrots have increased. the beak size of 4 10%. It is not something that you will immediately notice when looking at birds, but it is a measurable and functional difference for birds. “
Ryding also pointed out that it was intriguing that “Alaskan shrews have also increased their tail length, which I think is particularly interesting given that it is a completely different animal, in a completely different place in the world “.
This particular manifestation of Allen’s Rule is also a testament to how climate change threatens biodiversity. Last year, the World Wide Fund for Nature (WWF) reported that the size of populations of “mammals, birds, amphibians, reptiles and fish” fell 68% since 1970. Although it is probably impossible to quantify To what extent this has been caused by climate change, WWF also noted that people are over-exploiting the planet’s biocapacity by at least 56 percent.
“The precipitous global decline in wildlife populations is a key indicator that ecosystems are at risk,” Jeff Opperman, senior global freshwater scientist at the World Wide Fund for Nature at the time, told Salon. and co-author of the freshwater section of the report. . âHealthy ecosystems provide a range of benefits to humans, such as clean water, clean air, a stable climate, protection against flooding and the pollination of food crops. When populations decline and ecosystems begin to degrade, nature’s ability to support human health and livelihoods collapses.
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