The variety of life on Earth, known as biodiversity, represents the biological infrastructure that supports planetary health. This immense range of organisms and ecosystems forms the complex web of interactions that regulate our environment, from the microscopic level to the global scale of oceans and forests. Preserving the richness of life is a foundational requirement for maintaining the natural systems that provide clean air, fresh water, and food security. The stability and function of every ecosystem are directly tied to the extent of its biological diversity.
Defining Biodiversity and Its Levels
Biodiversity is measured across three distinct, interconnected levels, each contributing to the overall robustness of life.
The most fundamental level is genetic diversity, which is the variation in genetic material within a single species or population. This variation, like different strains of a crop species, allows a population to adapt to new diseases or changing environmental conditions, such as drought or heat.
The next level is species diversity, the most commonly recognized form, referring to the number of different species in a given area (richness) and their relative abundance (evenness). Ecosystems with many different types of organisms, such as a tropical rainforest, exhibit high species richness. Finally, ecosystem diversity describes the variety of habitats, biological communities, and ecological processes across a landscape, ranging from deserts and grasslands to coral reefs and wetlands.
Hotspots: Where High Biodiversity Occurs
High biodiversity is concentrated in specific regions known as biodiversity hotspots. These areas possess an unusually high concentration of endemic species—those found nowhere else—and have lost at least 70% of their original native vegetation. To qualify, a region must harbor a minimum of 1,500 endemic vascular plant species, making these locations irreplaceable and severely threatened.
These 36 globally recognized hotspots cover only about 2.5% of the Earth’s land surface and include the Atlantic Forest in Brazil, Sundaland in Southeast Asia, and the Caribbean Islands. Concentrations are often fueled by factors like long periods of climate stability, which allow species to evolve without major disruption. Geographical isolation, such as on islands or mountain ranges, also promotes the evolution of unique, endemic life forms.
Ecosystem Stability and Function
High biodiversity directly influences ecosystem stability through the insurance hypothesis. This concept states that a greater number of species increases the probability that some will maintain function even when others fail. This functional redundancy means that if one pollinator species declines, another can take its place, ensuring the continued service of pollination. Diverse ecosystems exhibit greater resilience, which is the ability to absorb a disturbance, like a severe drought or flood, and recover quickly to their original state.
The presence of many different species also optimizes resource utilization, leading to higher overall productivity. For example, a grassland with a variety of plant species captures sunlight, water, and soil nutrients more efficiently than a monoculture. This biological richness underpins numerous ecosystem services, such as the decomposition of organic matter that fuels nutrient cycling, the biological control of pests, and the regulation of atmospheric composition through carbon storage in forests and wetlands.
Major Drivers of Loss
The primary causes of declining biodiversity are almost entirely human-driven, with the leading factor being the conversion of natural habitats for human use. The destruction and fragmentation of forests, wetlands, and grasslands, largely for agricultural expansion, is the most significant threat, putting a majority of species at risk of extinction. This land-use change removes the physical space and resources that species need to survive and reproduce.
Climate change acts as a compounding driver, altering temperature and precipitation patterns faster than many species can adapt, shifting habitats, and increasing the frequency of extreme weather events. Other major pressures include the overexploitation of resources, which manifests as unsustainable overfishing and overhunting that depletes wild populations. The introduction of invasive species and widespread pollution, such as nitrogen runoff from agricultural activities, further disrupts ecological balances, accelerating the loss of biological variety.