One Rule Explains Life From Ocean Depths to Savannas

Scientists have discovered a simple rule that governs how life organizes itself across Earth’s most diverse ecosystems. From tropical rainforests to ocean depths, over 30,000 species follow the same spatial pattern regardless of whether they fly, swim, crawl, or remain rooted in place.

This new research, published in Nature Ecology & Evolution, reveals that biodiversity arranges itself in predictable layers radiating outward from dense cores to sparse transition zones—a pattern that holds true everywhere from amphibians in the Amazon to rays in the Pacific Ocean.

The discovery challenges expectations that different life forms would organize themselves differently across Earth’s varied landscapes. Instead, researchers found what they call a “core-to-transition” organization that appears to be a fundamental principle governing life on our planet.

Universal Pattern Across Life Forms

“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,” explains Rubén Bernardo-Madrid, lead author and researcher at Umeå University.

The international team examined seven dramatically different groups of organisms: amphibians, birds, dragonflies, mammals, marine rays, reptiles, and trees. These creatures employ vastly different survival strategies—some are warm-blooded, others cold-blooded; some are mobile, others stationary; some live in water, others on land.

What makes the finding remarkable is that despite these fundamental differences in biology and habitat, every group organizes itself according to the same spatial rule across the planet’s major biogeographical regions.

Environmental Filters Shape Life’s Distribution

The research identifies environmental filtering as the mechanism driving this universal pattern. Only species capable of tolerating specific local conditions—such as extreme heat, cold, or drought—can survive as they venture away from their optimal core habitats into more challenging environments.

Using advanced computer algorithms, the team analyzed species distribution data and divided the world into seven distinct types of areas, each representing different combinations of species richness, geographic range sizes, and levels of endemism. These areas form ordered layers that consistently appear across different biogeographical regions.

Core areas typically contain the most species and the highest concentration of endemic species—those found nowhere else. As distance from these cores increases, the number of species decreases while the remaining species tend to have larger geographic ranges, suggesting they possess greater environmental tolerance.

Small Areas, Massive Impact

One of the study’s most striking findings involves the disproportionate importance of core areas. These biodiversity hotspots occupy approximately 30% of each biogeographical region’s surface but harbor about 90% of its species—a concentration far higher than would occur by random chance.

This discovery has profound implications for conservation efforts. The research suggests that protecting these relatively small core areas could preserve the vast majority of species within entire biogeographical regions, making them invaluable targets for international conservation initiatives.

“The predictability of the pattern and its association with environmental filters can help to understand better how biodiversity may respond to global change,” says Joaquín Calatayud, co-author from Rey Juan Carlos University.

Testing the Theory

To validate their environmental filtering hypothesis, researchers examined whether different biogeographical sectors occupied areas with distinct environmental conditions. Using temperature and precipitation data for terrestrial species and temperature and salinity data for marine species, they found that 97.7% of cases showed clear environmental distinctions between different sectors.

The team also analyzed whether species composition changes between sectors resulted from species replacement (turnover) or from one area containing a subset of another’s species (nestedness). In 77% of biogeographical regions across all studied groups, the differences were primarily due to nestedness—supporting the idea that species spread outward from cores but only the most adaptable survive in peripheral areas.

Evolutionary Insights and Climate History

The core-to-transition pattern appears linked to deep evolutionary and climatic history. Core areas likely represent ancient centers of species diversification or past climate refugia where organisms survived during harsh periods like ice ages. These areas then served as sources from which species with better dispersal abilities and environmental tolerance spread to colonize surrounding regions.

Additional analysis revealed that climate changes since the Last Glacial Maximum also correlate with the observed patterns, suggesting that historical climate events helped shape the current organization of life on Earth.

Global Implications for Species Richness

The research addresses a fundamental question in ecology: what determines local species richness across the globe? The study found that regional environmental filtering—the process underlying the core-to-transition organization—can be as important as traditional factors like speciation and extinction rates in explaining why some places have more species than others.

Through mathematical modeling, researchers demonstrated that the sorting of species within biogeographical regions explains a substantial portion of global variation in local species richness. This challenges traditional approaches that focus primarily on regional species pool sizes and highlights the importance of understanding environmental filtering processes.

Conservation and Climate Change

The universal nature of this organizing principle offers new tools for predicting how ecosystems might respond to environmental changes. As climate change alters temperature and precipitation patterns worldwide, understanding these core-to-transition dynamics could help scientists anticipate which species and regions face the greatest risks.

The findings also suggest that conservation strategies should prioritize identifying and protecting core areas, which serve as biodiversity reservoirs for entire regions. These areas not only harbor the most species but also likely serve as sources for recolonizing disturbed habitats.

Methodology and Validation

The researchers employed sophisticated network analysis techniques, treating species and geographic locations as interconnected nodes in a complex system. They used the Infomap algorithm to identify biogeographical regions and their characteristic species, then applied machine learning clustering methods to reveal the seven types of biodiversity areas.

To ensure their findings weren’t artifacts of their analytical approach, the team conducted extensive sensitivity analyses using different numbers of clusters and various geographical scales. The core-to-transition pattern remained consistent across all tests, strengthening confidence in the results.

The study represents one of the most comprehensive analyses of global biodiversity organization ever conducted, spanning multiple continents, life forms, and habitat types while maintaining methodological consistency across all analyses.

This research provides a new lens for understanding life on Earth, suggesting that beneath the planet’s overwhelming biological diversity lies a remarkably simple and universal organizing principle that transcends the boundaries between land and sea, plant and animal, mobile and stationary life forms.