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Here’s what you’ll learn when you read this story:
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The organization of life on Earth follows a simple, hidden rule known as “core-to-transition organization.”
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Hypothesized by biogeographers for centuries, a new study finally finds empirical evidence of this phenomenon using geographic dispersion data across five separate taxa.
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This shows how a majority of species originate from “core regions,” but those species suitable to heat and drought often colonize areas beyond those regions.
The Earth is home to incredibly remarkable and diverse biomes that host millions of species worldwide. (George Lucas managed to create an entire galaxy far, far away for Star Wars using just the natural wonders mostly found in the state of California.) Although life appears relatively well-distributed across countries and continents—barring Antarctica, of course—a new study suggests that biodiversity isn’t so much an evenly distributed blanket across the planet as it is a “core-to-transition” organization.
This is the insight gleaned from a new article—published earlier this month in the journal Nature Ecology & Evolution—analyzing how organisms are divided into biogeographical regions, or bioregions, across the planet’s surface. An international team of scientists from Sweden, Spain, and the U.K. examined the global distribution maps of species across a variety of limbs on the tree of life, including amphibians, birds, dragonflies, mammals, marine rays, reptiles, and even trees. Because of this vast swath of differing types of life, the researchers expected that species distribution would vary wildly due to environmental and historical factors.
However, what they discovered is that life all around the world proliferates through a very similar process. First, there is a core area where life appears to flourish, and from there, species tend to radiate outward—hence “core-to-transition” organization.
“In every bioregion, there is always a core area where most species live,” Rubén Bernardo-Madrid, a co-author of the study from Umeå University, said in a press statement. “From that core, species expand into surrounding areas, but only a subset manages to persist. It seems these cores provide optimal conditions for species survival and diversification, acting as a source from which biodiversity radiates outward.”
These “core” regions are immensely important, as they only cover about 30 percent of the world’s surface but contain more biodiversity than the other 70 percent. These regions likely evolved because they were originally refuges from the devistation brought on by past climatic events, such as the Last Glacial Maximum. The study also shows that overall species must be well adapted for heat and drought to colonize new areas beyond these core bioregions.
“The predictability of the pattern and its association with environmental filters can help to better understand how biodiversity may respond to global change,” Joaquín Calatayud, co-author of the study from Rey Juan Carlos University, said in a press statement.
Of course, this core-to-transition organization idea isn’t a new one. Biogeographers have largely illustrated this phenomenon over the centuries, but this is the first time that empirical evidence has confirmed these long-standing suspicions. Understanding the relationship between life and these bioregions can help inform conservation decisions while predicting how certain species may respond to a new type of climatic uncertainty—anthropogenic climate change.
“Our core-to-transition hypothesis and results,” the authors wrote, “show that global variations in species richness can be better understood by unravelling the genesis of regional hotspots and the subsequent filtering of species to the rest of the biogeographical region.”
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