Biodiversity 101: Genes, Species and Ecosystems
Why this lesson matters
TNFD disclosures require organisations to understand and articulate their interactions with nature. That starts here: with a precise understanding of what biodiversity actually is, how it is organised across three interconnected levels, and why its current state demands urgent financial attention.
What Is Biodiversity?
The word "biodiversity" is shorthand for biological diversity, the variety of life on Earth in all its forms and at all levels of organisation. It is not simply a count of species. It encompasses the genetic variation within each species, the full range of species themselves, and the complex ecological communities those species form together.
The Convention on Biological Diversity (CBD), the foundational international treaty on the subject, defines biodiversity as "the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems." That single sentence captures all three levels we explore in this lesson.
Level 1: Genetic Diversity
Genetic diversity refers to the variation in DNA sequences among individuals within a single species. It is the raw material on which natural selection acts, and it determines a population's capacity to adapt to changing conditions.
Consider two scenarios. A population of wild wheat with high genetic diversity contains individuals with varying tolerance to drought, heat, and fungal disease. When a new pathogen emerges, some individuals survive and pass on their resistance. A population of a commercially bred monoculture wheat variety has low genetic diversity. A single novel pathogen can devastate the entire crop in a single season, as happened with the Irish potato famine of the 1840s, where the reliance on a single genetic variety of potato made the crop catastrophically vulnerable to Phytophthora infestans.
Analogy: Genetic Diversity as a Financial Portfolio
A genetic monoculture is like a portfolio with a single asset. If that asset crashes, everything is lost. A genetically diverse population is like a diversified portfolio across many asset classes: when one investment underperforms, others buffer the loss. Nature's resilience and, by extension, the reliability of the ecosystem services businesses depend on, is built on this diversification principle.
For business, genetic diversity matters in several concrete ways:
- The pharmaceutical industry derives approximately 50% of approved drugs from natural compounds or their derivatives, many discovered through screening genetically diverse wild species.
- Global crop production depends on wild relatives of cultivated plants for breeding traits such as drought tolerance. The CGIAR system maintains gene banks with over 760,000 accessions precisely to preserve this genetic insurance.
- Fisheries and aquaculture operations face collapse risk when they draw from genetically narrow breeding stocks, as witnessed in multiple salmon farming disease outbreaks.
Level 2: Species Diversity
Species diversity is the most familiar level of biodiversity. It encompasses two dimensions: species richness (the number of different species in an area) and species evenness (how equally abundant those species are). A forest with 100 species, each with similar population sizes, is more diverse than one where a single dominant species accounts for 90% of individuals.
Current estimates suggest there are approximately 8.7 million eukaryotic species on Earth, of which only around 1.5 million have been formally described. The IPBES Global Assessment (2019) found that approximately 1 million plant and animal species are currently threatened with extinction, many within decades. This is a rate 10 to 100 times higher than the natural background extinction rate averaged over the past 10 million years.
| Taxonomic Group | Known Species | Estimated Threatened | Key Driver of Loss |
|---|---|---|---|
| Amphibians | ~8,000 | 41% | Chytrid fungus, habitat loss |
| Corals (reef-building) | ~800 | 33% | Ocean warming and acidification |
| Mammals | ~5,500 | 26% | Land use change, hunting |
| Birds | ~11,000 | 14% | Agriculture, invasive species |
| Flowering plants | ~350,000 | ~10% | Habitat destruction, climate change |
Level 3: Ecosystem Diversity
Ecosystem diversity refers to the variety of habitats, biological communities, and ecological processes across a landscape or the entire planet. An ecosystem combines living organisms (the biotic component) with their physical environment (the abiotic component: soils, water, climate) in an integrated unit through which energy flows and nutrients cycle.
Major ecosystem types include:
- Tropical rainforests: Covering around 6% of Earth's land surface but hosting over 50% of the world's terrestrial species. They are primary carbon sinks and regulate regional rainfall patterns critical to agriculture across entire continents.
- Wetlands (marshes, swamps, peatlands): Covering approximately 6% of Earth's land area but storing more carbon per hectare than any other ecosystem. They filter water, reduce flood peaks, and support rich food webs.
- Coral reefs: Occupying less than 0.1% of the ocean floor but providing habitat for around 25% of marine species and protecting an estimated 200 million people from coastal flooding and erosion.
- Temperate grasslands and savannas: Home to the world's most productive agricultural soils; their conversion to cropland has been one of the primary drivers of terrestrial biodiversity loss.
- Open oceans: Covering 70% of Earth's surface and producing roughly 50% of the oxygen we breathe through phytoplankton photosynthesis.
Example: The Mangrove as a Multi-Level Biodiversity Asset
Mangroves illustrate all three levels simultaneously. At the genetic level, individual mangrove populations carry distinct adaptations to salinity and tidal exposure. At the species level, a single hectare may support 40+ fish species, dozens of bird species, and hundreds of invertebrate species. At the ecosystem level, mangrove forests sequester carbon at rates 3 to 5 times greater than tropical inland forests, filter coastal water, and provide nursery habitat for commercially important fish and shellfish. The World Resources Institute estimates that intact mangrove forests prevent over $65 billion in flood damages annually. Their loss therefore represents simultaneous collapse across all three biodiversity levels and all associated economic functions.
The Current State of Global Biodiversity
The IPBES Global Assessment (2019), the most comprehensive scientific review ever conducted on the state of nature, assessed evidence across 15,000 scientific and government sources over three years. Its headline findings are sobering and directly relevant to any organisation conducting TNFD-aligned nature risk assessments.
- The global average abundance of native species in major land-based habitats has fallen by at least 20% since 1900.
- More than 40% of amphibian species, almost 33% of reef-forming corals, and more than 33% of marine mammals are threatened.
- At least 680 vertebrate species have been driven to extinction since the 16th century.
- The biomass of wild mammals has fallen by 82%; human-produced material (concrete, plastics, asphalt) now exceeds all living biomass on Earth.
- Native insect populations in monitored areas have declined by a third, threatening the pollination services underpinning roughly 75% of global food crop types.
The Planetary Boundaries framework, developed by the Stockholm Resilience Centre, identifies nine Earth system boundaries within which humanity can safely operate. Biosphere integrity (biodiversity) is identified as one of the two "core" boundaries, alongside climate change, because crossing it could trigger irreversible state changes in other systems. Current estimates place us already beyond a safe boundary for biosphere integrity: the current rate of biodiversity loss far exceeds the proposed "safe" limit of fewer than 10 extinctions per million species-years. For organisations and investors, operating within planetary boundaries is increasingly framed as the foundational condition for long-term economic stability.
Key Takeaways
- 1Biodiversity operates across three interconnected levels: genetic diversity (variation within species), species diversity (variety of species), and ecosystem diversity (variety of habitats and ecological communities)
- 2Genetic diversity functions like a biological insurance policy, enabling populations and the businesses that depend on them to adapt to changing conditions
- 3Approximately 1 million plant and animal species are currently threatened with extinction according to the IPBES 2019 Global Assessment, at a rate 10 to 100 times the natural background rate
- 4Ecosystem diversity underpins the provisioning, regulating, cultural, and supporting services that generate an estimated $44 trillion in annual economic value globally
- 5Loss at any one level cascades to the others: losing species reduces ecosystem function; losing ecosystems erodes the habitat that genetic diversity depends on