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The variety of all living organisms (genes, species, ecosystems) within a given area; measured at three levels: genetic, species, and ecosystem.

The total number of different species present in an ecosystem or area; a simple measure of biodiversity that doesn't account for relative abundance.

The relative abundance or proportional representation of each species within a community; high evenness means species numbers are balanced; low evenness indicates dominance by few species.

A quantitative measure of biodiversity that incorporates both species richness and evenness; higher values indicate greater biodiversity; ranges 1.5–3.5 in most ecosystems.

Destruction, fragmentation, or degradation of natural ecosystems; the leading global threat to biodiversity, driven by land-use conversion (agriculture, urbanisation, logging).

Non-native organisms introduced (accidentally or deliberately) that outcompete native species for resources, alter food webs, and reduce genetic diversity; second-largest threat after habitat loss.

Unsustainable harvest of wild populations beyond regeneration capacity; examples include overfishing, deforestation, wildlife poaching; threatens species survival and ecosystem stability.

Alters temperature/precipitation regimes, shifts growing seasons, raises sea levels; species cannot adapt or migrate fast enough; disrupts phenology and predator–prey relationships; fastest-growing threat.

Energy enters via photosynthesis (primary producers); flows through trophic levels (consumers); approximately 10% transferred at each level due to respiration and heat loss; remainder lost as waste.

Food chain: linear sequence of organisms (e.g. grass→rabbit→fox); Food web: interconnected multiple chains showing realistic feeding relationships and energy pathways in an ecosystem.

Continuous cycling of nitrogen between atmosphere, soil, and biota: nitrogen fixation (atmospheric N₂ → ammonia via bacteria), nitrification (ammonia → nitrate), assimilation (plants/animals), denitrification (nitrate → N₂).

Movement of phosphorus through rock/soil, organisms, and water: weathering releases phosphate; uptake by plants and animals; decomposition returns P to soil; no atmospheric phase; limiting nutrient in many ecosystems.

Long-term removal and storage of atmospheric CO₂ in sinks (forests, soils, oceans); key climate mitigation tool; forests store ~296 Pg C; important for net-zero targets.

Large core area, minimised edge-to-area ratio, physical connectivity, multiple reserves rather than single site (SLOSS debate), buffering against external threats, active management.

Linear connections (riparian zones, wildlife bridges, green belts) linking fragmented habitats; allow species movement, gene flow, and range expansion; buffer against habitat isolation.

Emergent layer (tallest trees, 40–60 m); canopy (dense, intercepts most light); understory (shade-adapted); forest floor (thick litter, fungi-rich); 50% of terrestrial species; high nutrient cycling.

Cattle ranching (80% Amazon loss), logging, agriculture (soy, palm oil), infrastructure (roads, dams), mining, slash-and-burn; externalities: carbon release, species extinction, hydrological disruption.

Economic viability, environmental integrity, social equity; must balance profit, ecological limits, and human wellbeing; intersection point = true sustainability.

Measurable variables reflecting ecosystem or social health (e.g. GDP, carbon footprint, literacy, biodiversity index); track progress toward Sustainable Development Goals; inform policy.

Human activities (fossil fuels, agriculture, deforestation) increase atmospheric greenhouse gases (CO₂, CH₄, N₂O); trap more heat than natural; average global temperature rises ~1.1°C since 1880.