The global rule that predicts where life thrives—and where it fails

The research team led, by Umeå University and involving the University of Reading, believe this rule helps explain why species are spread the way they are across the planet. The discovery will help to understand life on Earth - including how ecosystems respond to global environmental changes.

The rule is simple: in every region on Earth, most species cluster together in small 'hotspot' areas, then gradually spread outward with fewer and fewer species able to survive farther away from these hotspots.

Rubén Bernardo-Madrid, lead author and researcher at Umeå University (Sweden), said: "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. It seems these cores provide optimal conditions for species survival and diversification, acting as a source from which biodiversity radiates outward."

This pattern highlights the disproportionate ecological role these small areas play in sustaining the biodiversity of entire bioregions. Jose Luis Tella, from the Estación Biológica de Doñana-CSIC (Spain), said: "Safeguarding these core zones is therefore essential, as they represent critical priorities for conservation strategies."

Environmental filtering

Researchers studied bioregions across the world, examining species from very different life forms: amphibians, birds, dragonflies, mammals, marine rays, reptiles, and trees. Given the vast differences in life strategies -- some species fly, others crawl, swim, or remain rooted -- and the contrasting environmental and historical backgrounds of each bioregion, the researchers expected that species distribution would vary widely across bioregions. Surprisingly, they found the same pattern everywhere.

The pattern points to a general process known as environmental filtering. Environmental filtering has long been considered a key theoretical principle in ecology for explaining species distribution on Earth. Until now, however, global empirical evidence has been scarce. This study provides broad confirmation across multiple branches of life and at a planetary scale.

Professor Manuela González-Suárez, co-author of the study at the University of Reading, said: "It doesn't matter whether the limiting factor is heat, cold, drought, or salinity. The result is always the same: only species able to tolerate local conditions establish and persist, creating a predictable distribution of life on Earth."

The existence of a universal organising mechanism has profound implications for our understanding of life on Earth. Joaquín Calatayud, co-author from the Rey Juan Carlos University (Spain), said: "This pattern suggests that life on Earth may be, to some extent, predictable." Such predictable patterns can help scientists trace how life has diversified through time and offer valuable insights into how ecosystems might react to global environmental changes.