Definition

Biodiversity means the variety of living things in a place, so a rainforest with thousands of kinds of trees, birds, insects, and frogs has high biodiversity while a cornfield growing mostly corn has low biodiversity, and biodiversity works like a safety net with many strands: if one strand breaks, the rest still hold, while a net with only a few strands falls apart. More formally, biodiversity spans genetic diversity within a species, species diversity within a community, and ecosystem diversity across a region, with more diverse ecosystems tending to be more stable, more productive, and quicker to recover from disturbance, while biodiversity itself is threatened by habitat loss, invasive species, pollution, overharvesting, and climate change, and runs highest in the tropics and in hotspots such as coral reefs. At the measurement level, biodiversity is quantified as genetic diversity (allelic richness, heterozygosity), species diversity (richness and evenness, often summarized by Shannon or Simpson indices), functional diversity (the range of ecological roles), and ecosystem diversity, with experimental grassland studies showing productivity, nutrient retention, and stability all rising with species richness through complementarity and insurance effects; its spatial patterns follow the latitudinal diversity gradient, species-area relationships, and island biogeography theory, and current extinction rates, estimated at $100$ to $1{,}000$ times background, have prompted talk of a sixth mass extinction, with conservation prioritizing hotspots, keystone and umbrella species, and connectivity.