Biodiversity loss

Biodiversity loss operates at genetic, species, and ecosystem levels, so extinction is only its most irreversible form. A population may decline sharply while its species survives elsewhere; local extirpation can nevertheless remove ecological functions and genetic adaptations. The loss of genetic diversity can make crops, livestock, and wild populations less resilient to disease, drought, and warming.

Human pressures have transformed much of the planet. IPBES reported that three-quarters of the terrestrial environment and about two-thirds of the marine environment had been significantly altered by human activity. ¹ Tropical forests, freshwater systems, islands, coral reefs, and coastal wetlands are especially vulnerable because they contain many narrowly distributed species. The IUCN Red List tracks extinction risk, but its assessments cover only a fraction of all described species and an even smaller fraction of those not yet scientifically documented. ³

Habitat destruction and degradation are the largest direct global pressures on terrestrial biodiversity, while overexploitation is particularly important in many marine and freshwater environments. ¹ Conversion of forests and grasslands to farms, roads, mines, and settlements removes habitat and fragments what remains. Small, isolated patches can support fewer species, restrict movement, and expose forest interiors to heat, wind, fire, and predators.

Pollution alters air, water, and soil through nutrients, pesticides, plastics, heavy metals, and noise. Invasive species can outcompete, prey on, hybridize with, or transmit diseases to native organisms. Climate change shifts temperature and rainfall, changes seasonal timing, raises sea levels, and intensifies marine heatwaves; these effects increasingly interact with habitat loss and exploitation. The drivers are connected through consumption and trade, so reducing one pressure may not restore diversity if others remain high.

Biodiversity loss weakens ecological functions and can make ecosystems less able to withstand shocks. Fewer pollinators can reduce the reproduction of wild plants and crops; depleted predators can trigger food-web changes; and the disappearance of mangroves, reefs, and wetlands can increase exposure to storms and flooding. The effects are uneven: Indigenous peoples and local communities often depend directly on diverse fisheries, forests, rangelands, and medicinal species, while poorer households generally have fewer alternatives when these resources decline.

Responses combine protection, sustainable use, restoration, and changes in production and consumption. Protected and conserved areas can safeguard habitat, but they work best when effectively governed and connected. Ecological restoration can recover some functions without recreating the original community, and preventing extinctions is usually more effective than attempting reintroduction after a species disappears. The Kunming–Montreal Global Biodiversity Framework sets targets including conserving at least 30% of land and inland waters and 30% of marine areas by 2030. ²

Biodiversity loss is often detected first through changes in abundance, range, or ecological role rather than through extinction. A common species can become rare enough to lose its function, while a few tolerant species increase and create an apparently healthy but biologically simplified landscape. Scientists describe this process as biotic homogenization: different regions come to contain increasingly similar species, often because widespread generalists replace local specialists.

Some losses are cryptic. Soil organisms, fungi, parasites, insects, deep-sea species, and microorganisms remain poorly surveyed, so declines may precede formal recognition. Genetic erosion can also occur in species whose population counts appear stable, especially when isolated groups interbreed less often. Conservation therefore uses environmental DNA, acoustic monitoring, museum collections, and long-term ecological surveys alongside direct counts. Small refuges, seasonal habitats, and migration corridors can matter disproportionately, while invasive species may be beneficial in one altered setting yet harmful where they displace native species. Global assessments emphasize that reversing decline requires addressing underlying economic and institutional drivers, not only creating reserves. ¹

Biodiversity

The variety of life at genetic, species, and ecosystem levels.

Habitat fragmentation

The division of continuous habitat into smaller, more isolated patches.

Genetic diversity

Variation in inherited traits within and among populations.

Extirpation

The disappearance of a species from a particular area while it survives elsewhere.

Biotic homogenization

The increasing similarity of species communities across different places.