The big blue banana crane at the Entebbe Botanical Garden in Uganda
Researchers have demonstrated how millions of years of climate change affected the range and habitat of modern birds, suggesting that many groups of tropical birds may be relatively new in equatorial households.
Researchers from the Universities of Cambridge and Oxford applied climate and ecological models to illustrate how the distribution of major birds relates to climate change over millions of years.
However, while past climate change often occurred slowly enough for species to adapt or change habitat, the current rate of climate change may be too fast for many species, putting them at risk of extinction.
The results of this study are reported in the Proceedings of the National Academy of Sciences.
Co-lead author of the paper, Dr Daniel Field, from the University of Cambridge's Department of Earth Sciences, said: "Paleontologists have documented a long-term link between climate and the geographical distribution of major bird populations, but to date the computer models needed to quantify this link have not been applied to this problem. ”
Ancient supercontinent of Gondwana
In the current study, the researchers looked at 10 bird populations currently limited to the tropics that once lived mainly on the ancient supercontinents of Gondwana (Africa, South America and Australasia). However, early fossil representations of these groups have been found on the northern continent, well beyond their current range.
White-crowned banana cuckoo in the wilderness of South Africa's Western Cape
For example, the "turacos", a fruit-eating bird found only in the forests and savannahs of sub-Saharan Africa, but fossils of early relatives of the banana cuckoo have been found in the modern-day northern U.S. state of Wyoming.
Today, Wyoming is too cold for the banana crane for most of the year, but 66 million years ago, during the extinction of non-avian dinosaurs, the planet warmed. Over time, the global climate has cooled considerably, and the ancestors of these birds have gradually shifted their living range to more suitable areas.
Another lead author of the paper, Dr Erin Saupe of the University of Oxford, said: "We simulated the habitable area of each group of birds and found that their estimated habitable range in the past was very different from today's geographical distribution, and in all cases turned to the equator during geological periods. ”
Thorpe, Field, and their collaborators mapped information such as average temperatures and rainfall and linked it to the location of each flock of birds today. Using this climate information, they built an "ecological niche model" that plots suitable and unsuitable areas for each flock of birds. They then projected these eco-niche models onto paleoclimate reconstructions to map habitats that might have been suitable for millions of years.
The researchers were able to predict the geographic location represented by the fossils of these groups at different points in Earth's history. These fossils provide direct evidence that these groups were previously distributed in different parts of the world.
"We've looked at the extent to which the right climate determines the location of these animal groups in the past and where they are now," Field said. Based on climate change projections, this approach also allows us to estimate their future end results. ”
"Many of these groups do not contain a large number of biological species, but each lineage represents millions of years of unique evolutionary history," Thorpe said. In the past, climate change occurred slowly enough that groups were able to find suitable habitats as these habitats moved around the globe, but now climate change is happening much faster and it could lead to the extinction of entire branches of the tree of life in the near future. “