Biodiversity is the variety and variability of living organisms and the ecological systems in which they occur. It encompasses differences within species, between species, and among ecosystems, rather than simply the number of kinds of organisms in a place. The definition used by the Convention on Biological Diversity includes terrestrial, marine, and other aquatic life and their ecological complexes. Biodiversity therefore concerns both biological components and the relationships connecting them. (cbd.int)
Levels of biodiversity
Three interconnected levels provide a common framework for describing biodiversity:
- Genetic diversity is variation within species, including differences among individuals and populations. It encompasses inherited differences associated with genes and includes variation among crop varieties and livestock breeds as well as wild populations.
- Species diversity concerns the variety of species and their relative representation within a community or region.
- Ecosystem diversity concerns the variety of ecological systems, including their living communities, physical environments, and interactions. A landscape containing woodland, grassland, and wetlands represents diversity at this level. (cbd.int)
These levels are related but not interchangeable. A species can persist while losing genetic variation, and an ecosystem can retain a similar species count while its composition changes. Biodiversity includes domesticated organisms and inconspicuous life, such as microorganisms, as well as familiar plants and animals. Its scope is consequently wider than wildlife alone. (cbd.int)
Measurement and interpretation
There is no single measure that captures every dimension of biodiversity. Species richness counts the species recorded in a defined area. Evenness describes how equally individuals are distributed among those species. Two communities may have identical richness but differ markedly if one is dominated by a single species while the other contains similar numbers of each. Counts therefore need to be interpreted alongside abundance and composition. (nps.gov)
Other approaches examine genetic variation, ecological traits, or evolutionary relationships. Functional diversity describes differences in characteristics relevant to ecological processes, such as feeding strategies or resource use. Measures incorporating evolutionary relationships distinguish diversity among closely related organisms from diversity spanning more distant lineages. These perspectives can reveal changes that species counts alone overlook. (cbd.int)
The choice of indicator depends on the question being investigated. Assessments may consider population abundance, the distribution of organisms, ecosystem extent, or changes in genetic variation. Richness alone is an incomplete indicator because biodiversity also has dimensions of quantity, location, and ecological role. A meaningful comparison must therefore specify which component is being measured rather than treat all biodiversity indicators as equivalent. (cbd.int)
Evolutionary origins
Biodiversity is a product of evolution. Organisms have diversified as inherited variation, environmental conditions, and natural selection shaped successive generations. The fossil record documents changes in life through time, including the appearance and disappearance of groups. Evidence from genetics, anatomy, and molecular biology complements fossils in reconstructing this history. Present-day biodiversity represents surviving branches of that evolutionary history, not a fixed or unchanging inventory. (nps.gov)
Ecological relationships also shape how diversity functions. Organisms interact with one another and with their physical surroundings, so the consequences of losing a species depend partly on its role and connections. The ecosystem approach in ecology and conservation accordingly examines relationships within species, among species, and between organisms and their environments, rather than considering each biological component in isolation. (cbd.int)
Ecosystem functioning and human significance
Biodiversity influences processes such as biomass production and decomposition. Species can differ in how they acquire resources and contribute to ecological functions. Experimental research has demonstrated links between diversity and ecosystem performance: a decade-long grassland experiment found that greater plant species richness increased both productivity and the temporal stability of production. (nature.com)
These relationships are context-dependent. Stability can mean resistance to disturbance, recovery afterward, or reduced fluctuations over time, and these properties do not necessarily respond alike. Experiments have found cases in which greater diversity increased temporal stability but reduced resistance to warming. Thus, biodiversity does not imply that every ecosystem function or every measure of stability will increase uniformly. (nature.com)
Human benefits associated with living systems are often described as ecosystem services. They include food and biological materials, pollination, and regulation of environmental conditions. Biodiversity also has cultural significance and provides genetic resources used in agriculture and other activities. Its value is not limited to immediately marketable products; the Convention recognizes ecological, genetic, scientific, cultural, and intrinsic values. (ipbes.net)
Loss and major pressures
Biodiversity loss includes declining populations, erosion of genetic variation, degradation of ecosystems, and extinction. In its 2019 global assessment, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services estimated that around one million animal and plant species were threatened with extinction. This was an assessment-based estimate, not a count of species already extinct. (ipbes.net)
The assessment identified five major direct drivers: changes in land and sea use, direct exploitation of organisms, climate change, pollution, and invasive alien species. Their importance differs among environments. Land-use change was the largest relative driver in terrestrial and freshwater systems, whereas direct exploitation, particularly fishing, had the largest relative impact in marine systems. These pressures may operate simultaneously. (ipbes.net)
Conservation and international frameworks
Conservation includes protecting organisms in their natural habitats, maintaining populations outside those habitats, promoting sustainable use, and undertaking ecological restoration. The Convention distinguishes in situ conservation within natural surroundings from ex situ conservation outside them. Its three objectives are conservation, sustainable use, and fair and equitable sharing of benefits arising from genetic resources. (cbd.int)
Adopted in December 2022, the Kunming–Montreal Global Biodiversity Framework establishes 23 targets for 2030. They include placing at least 30 percent of terrestrial and inland-water areas, and marine and coastal areas, under effective conservation and management, and ensuring that at least 30 percent of degraded ecosystems are under effective restoration. The conservation target also specifies ecological representation, connectivity, equitable governance, and respect for Indigenous peoples’ and local communities’ rights. (cbd.int)