Biodiversity everywhere is ordered by a common ‘hidden’ pattern

Basics & Context

• Biogeographical regions:
  • Earth divided into large regions (e.g., Nearctic, Afrotropical, Indo-Malayan) hosting unique species shaped by history, climate, barriers (oceans, mountains).
  • For two centuries, assumed that inner layouts of species within each region were idiosyncratic.
• Known global rule:
  • Tropics richer in biodiversity, poles poorer.
  • But: is there a universal rule within each region?
• New finding (Nature Ecology & Evolution, July 2025):
  • Biodiversity is structured like an onion → dense unique cores, grading outward to porous transition zones.

Relevance : GS 3(Environment and Ecology)

The Study: Methods

• Data used:
  • 30,000 species (birds, mammals, amphibians, reptiles, rays, dragonflies, trees).
  • Sources: IUCN Red List, BirdLife International, US Forest inventories.
• Approach:
  • Earth divided into equal-sized grid cells (~111 sq. km for land animals).
  • Recorded species in each cell.
  • Used Infomap (network analysis) → grouped co-occurring species into clusters = biogeographical regions.
  • Tagged species as:
    • Characteristic → core, endemic, tied to that region.
    • Non-characteristic → spill-over from neighbouring regions.
• Diversity metrics per cell:
  • Species richness, overlap, occupancy, endemicity.

Key Findings: The Onion Model

• Seven repeating biogeographical sectors → appeared in every major region, across all taxa.
• Layered structure:
  • Core hotspots: High richness, high endemicity, minimal outsiders.
  • Inner layers: Still rich, more widespread species.
  • Middle layers: Moderate richness, mix of characteristic & non-characteristic species.
  • Transition zones: Species-poor, dominated by wide-ranging generalists from multiple regions.
• Environmental filters:
  • 98% accuracy in predicting sector using only temperature + rainfall models.
  • Shows that only species tolerating local conditions persist.
• Subset principle:
  • Outer layers = fewer specialists, not entirely new assemblages.

Scientific Significance

• Universal rule: First large-scale, data-backed confirmation that biodiversity within regions follows a generalisable pattern.
• Ecological insight: Assemblage shaped by climate filters, not random distributions.
• Conceptual shift: From “messy quilt” to ordered layered mosaics of biodiversity.

Conservation Implications

• Target protection:
  • Core hotspots = highest payoff for conservation (rich + endemic + unique).
  • Transition zones = important for corridors and resilience under climate change.
• Climate change lens:
  • Rising temperatures and rainfall shifts → re-structuring of onion layers.
  • Example: Himalayas (already warming fast, rainfall shifting) → frontline for biodiversity turnover.
• Beyond protected areas:
  • Focus on altitudinal zones, habitat corridors, ecological gradients.
• Global South gaps:
  • Underrepresentation of dragonflies (Eurasia), trees (N. America), tropical taxa (India, Africa).
  • Need for regional research to complement global models.

Indian Context

• Himalayas & Western Ghats:
  • Core zones highly endemic (amphibians, plants).
  • Transition zones critical under climate-driven species migration.
• Policy relevance:
  • National Biodiversity Mission (NBM), National Wildlife Action Plan → can integrate core-to-transition layering in site prioritisation.
  • Helps India balance conservation + development (hydropower, roads in Himalayas).
• Case study use in UPSC:
  • Supports questions on ecosystem resilience, biodiversity conservation, climate change adaptation strategies.

Critiques & Limitations

• Geographical gaps → some taxa and regions underrepresented.
• Data bias → relies heavily on well-studied groups, less on microbes/invertebrates.
• Still correlative → shows patterns, not always causal mechanisms.

Way Forward

• Refine models with more regional data (esp. tropics, Global South).
• Integrate with climate projections to predict biodiversity shifts.
• Policy uptake: Prioritise conservation in cores, maintain ecological connectivity in outer layers.
• Collaborative monitoring: Expand citizen science + global biodiversity inventories.

Conclusion

The “onion model” of biodiversity transforms our understanding of how life is organised across Earth’s regions. It reveals that biodiversity cores hold the densest, most unique life forms, while layers outward reflect climate filters and species tolerance. For conservation, this means protecting cores first while ensuring transition zones remain permeable to climate-driven movements — a sharper, more strategic lens for saf