Scientists discover one simple rule that explains all life on Earth

Stand on any hillside on Earth and the view jumps from desert to forest to coast, with each bioregion hosting its own cast of creatures. For decades, naturalists asked why a South American rainforest hosts parrots and jaguars while an African one shelters hornbills and leopards.

The explanation, many suspected, lies in the deep history of place, not just in climate or chance.

Fresh analysis of records for more than 30,000 species now points to a single thread that stitches those patches together.

The work hints at clearer forecasts of how ecosystems will react as the planet warms, dries, and becomes more crowded, and it offers practical clues for anyone trying to keep biodiversity intact.

Why nature clusters

The project came from Rubén Bernardo-Madrid of Umeå University, Joaquín Calatayud of Rey Juan Carlos University, and partners in Sweden, Spain, and the United Kingdom.

They sliced the globe into the well-known biogeographical regions and traced amphibians, birds, dragonflies, mammals, marine rays, reptiles, and trees across them.

Order appeared where chaos was expected. In every territory, the team found a robust center that shelters the majority of resident species.

“In every bioregion, there is always a core area where most species live. From that core, species expand into surrounding areas, but only a subset manages to persist,” Bernardo-Madrid explains.

“It seems these cores provide optimal conditions for species survival and diversification, acting as a source from which biodiversity radiates outward.”

Seven zones per bioregion

The team then mapped seven nested zones inside each bioregion, each with its own mix of widespread residents and highly local specialists. The central belt holds many species; the outer belts hold fewer but often unique ones.

The rule stayed intact whether the subject crawled, flew, swam, or rooted. Trees and marine rays may live worlds apart, yet their distributions echoed the same lattice from the Amazon Basin to Hudson Bay.

Each bioregion is bounded by barriers that discourage wanderers – an ocean trench, a desert interior, a frosty ridge. Over thousands of generations, those barriers steer evolution down separate paths.

Marsupials flourish in Australia because the surrounding sea keeps placental mammals at bay. Likewise, venomous vipers fill Central America but fade near the Andean wall.

Charles Darwin and Alfred Russel Wallace drew the first broad outlines of these divisions in the 1800s, yet their maps were blunt instruments.

Modern databases, satellite imagery, and museum collections now let researchers slice the globe with much finer resolution, revealing hidden borders such as Wallace’s Line between Borneo and Sulawesi, where Asian and Australasian fauna still collide.

How bioregion cores stay rich

Central zones usually enjoy milder temperatures, steadier rains, and larger habitat blocks – conditions that cushion populations against droughts, fires, or disease. Over time, those safe harbors spark new species, so the core doubles as nursery and archive.

Farther out, tougher climates and sharper competition thin the roster. The survivors often evolve in isolation, explaining why a corner of Madagascar or a Panamanian ridge can host creatures found nowhere else.

Environmental filtering, long a core idea in ecology, emerged as the engine behind the seven-zone scheme.

If an organism cannot cope with a site’s heat, salt, or altitude, it fails to gain a foothold. Global evidence for that rule had been patchy until now.

Calatayud notes, “The predictability of the pattern and its association with environmental filters can help us better understand how biodiversity may respond to global change.”

In practice, that insight lets conservation planners model vulnerability without guessing region by region.

Implications for conservation

Budgets for conservation are finite, and field crews often face tough choices on where to place fences or patrols. Knowing that a region’s biological bank lies in its core offers a clear target.

Guarding that nucleus secures most species, while a few carefully placed reserves at the fringes hold the irreplaceable endemics that give every landscape its distinct feel.

The Nature Ecology & Evolution paper highlights how a rainforest refuge the size of a county, or a string of barrier islands, can buoy entire landscapes. Protect those pockets from mining or ill-planned sprawl, and the wider biome stands a better chance.

Humans, bioregions, and the future

The new rule surfaces as humans alter habitats faster than many species can adjust, while warming nudges climatic bands roughly 12 miles north each decade.

With a consistent framework, researchers can forecast which cores may shrink or shift and where fresh refuges might form.

Some centers may have to leap uphill or poleward to survive, dragging dependent species along a gauntlet of highways, farms, and cities.

More data will sharpen those forecasts, yet the message is already clear. Biodiversity is not random; it follows a sturdy, planet-wide logic.

By working with that logic, communities can steer scarce resources toward the spots that quietly keep life thriving – and in turn secure our own future.

The full study was published in the journal Nature Ecology and Evolution.

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