15 ecosystems quietly running the planet, one species at a time

A few specific places on Earth contain a disproportionate share of all known species — and understanding why those places are so productive explains a great deal about how life works

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Biodiversity is not evenly distributed across the Earth's surface. Of the estimated eight to ten million species of plants, animals, fungi, and microorganisms that exist on Earth, a disproportionate share — the estimates vary but consistently suggest that more than half of all described species occupy less than 2% of the Earth's land surface — is concentrated in a small number of specific ecosystem types. These are not simply the largest ecosystems or the most ancient ones; they are the ones whose specific combinations of climate, geology, water, and evolutionary history have produced the conditions under which new species form fastest, existing species persist longest, and the interactions between species generate the complexity that characterizes the most productive biological communities on Earth.

Understanding why biodiversity concentrates where it does is one of the central questions of ecology, and the answers are multiple and interacting. Stable climates over long geological periods allow species to accumulate without the periodic extinction events that reset diversity in harsher environments. High primary productivity — the amount of solar energy converted into organic matter by plants — supports more species at every level of the food web. Structural complexity in the habitat — the three-dimensional architecture of a forest canopy or a coral reef — provides more distinct niches for different species to occupy. Geographic isolation produces speciation. The convergence of multiple habitat types at their boundaries — ecotones — supports species from adjacent communities simultaneously.

This list covers 15 ecosystems that exemplify these principles — environments whose specific characteristics have made them among the most species-rich places on Earth, and whose loss or degradation would represent a disproportionate reduction in the planet's total biological diversity. Several are formally recognized as biodiversity hotspots under the criteria developed by ecologist Norman Myers and subsequently adopted by Conservation International: areas that contain at least 1,500 endemic vascular plant species and have lost at least 70% of their original habitat extent. Others are not formally designated as hotspots but are among the most ecologically productive and biologically diverse environments known.

Each slide covers what the ecosystem is, why it is so biologically productive, what it contains, and the specific pressures it faces. The pressures are real and in most cases severe. The ecosystems on this list are not static museum pieces — they are dynamic, threatened, and in many cases shrinking faster than the species they contain can be described.

The Amazon $AMZN basin contains the largest tropical rainforest on Earth — approximately 5.5 million square kilometers of contiguous forest spanning nine South American countries, with Brazil containing approximately 60% of the total area. It is, by most measures, the most biodiverse terrestrial ecosystem on the planet: home to an estimated 10% of all species on Earth, including approximately 40,000 plant species, 1,300 bird species, 3,000 fish species, 430 mammal species, and an estimated two to three million insect species, of which the majority have not yet been formally described.

The Amazon's extraordinary biodiversity is a product of multiple interacting factors. The region has been continuously forested for tens of millions of years, providing the evolutionary stability that allows species to accumulate rather than being periodically reset by climate shifts or geological events. The uniformly warm, wet climate — most of the basin receives between 2,000 and 3,000 millimeters of rainfall annually — supports year-round primary productivity at rates that sustain an enormous biomass of plants and animals. The forest's three-dimensional structure — from the soil microbiome through the herb layer, understory, subcanopy, and emergent canopy trees reaching 50 meters or more — provides habitat niches of extraordinary variety.

The Amazon also generates its own climate. Approximately 20% of the water that falls as rain in the Amazon basin is water that was previously transpired by the forest itself — the trees pump water from the soil into the atmosphere, where it condenses and falls again in a self-sustaining cycle that the forest both depends on and creates. The hydrological cycle of the Amazon affects rainfall patterns across South America, including in the agricultural regions of southern Brazil and Argentina whose productivity depends on the rainfall that the intact Amazon generates.

Approximately 17% of the Amazon's original forest cover has been lost since 1970, with current deforestation rates fluctuating with Brazilian political cycles. Researchers at Brazil's National Institute for Space Research have estimated that the Amazon may be approaching a tipping point at approximately 20 to 25% deforestation, beyond which the hydrological cycle becomes self-disrupting and large areas of forest transition to savanna regardless of whether further deforestation occurs.

The Coral Triangle — the roughly triangular area of the western Pacific Ocean bounded by the Philippines, Indonesia, Malaysia, Papua New Guinea, the Solomon Islands, and Timor-Leste — is the global center of marine biodiversity, containing more coral species, fish species, and marine life generally than any other area of comparable size in the world's oceans. It covers approximately 6 million square kilometers of ocean and is home to approximately 76% of all known coral species, 37% of all known coral reef fish species, and six of the seven known marine turtle species.

The Coral Triangle's extraordinary biodiversity is the product of its position at the intersection of the Pacific and Indian Ocean basins, a location that has been at or near the center of tropical marine biodiversity for tens of millions of years. The region served as a refuge for marine life during glacial periods when sea levels dropped and other shallow water habitats were reduced or eliminated, and its position at the meeting point of two major ocean systems exposes it to the full range of Indo-Pacific marine species rather than the subset available in either ocean alone.

The reef systems within the Coral Triangle support the livelihoods of approximately 120 million people in the surrounding countries through fishing, coastal protection, and tourism. The Philippines alone has more fish species in its reefs than the entire Caribbean Sea, and the diversity of economically important fish species — grouper, tuna, snapper, and many others — makes the Coral Triangle one of the most important fisheries regions in the world.

The Coral Triangle faces multiple simultaneous threats: ocean warming, which produces coral bleaching events of increasing frequency and severity; ocean acidification, which reduces the ability of corals to build their calcium carbonate skeletons; destructive fishing practices including dynamite fishing and cyanide use; and coastal development. The 2016 mass bleaching event affected approximately 50% of the shallow-water corals on Australia's Great Barrier Reef, which lies adjacent to the Coral Triangle, in a demonstration of the speed at which climate change can produce large-scale ecosystem damage.

Cape Floristic Region

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The Cape Floristic Region — the southwestern tip of South Africa, centered on the area around Cape Town and extending approximately 90,000 square kilometers — is the smallest of the world's six major plant kingdoms and one of the most species-rich plant communities on Earth, containing approximately 9,000 plant species, of which approximately 70% are endemic (found nowhere else). This level of plant endemism in a temperate region is extraordinary — the entire United Kingdom has approximately 1,500 native plant species across an area 27 times larger.

The Cape Floristic........

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