Mammals live on every continent, in every ocean, and across nearly every habitat type on Earth. With roughly 6,760 recognized species, they occupy forests, deserts, grasslands, mountains, polar ice, underground burrows, open skies, deep oceans, and even city centers. No other warm-blooded group spans quite as many environments, from the seafloor to elevations above 6,000 meters.
Where Mammal Diversity Is Highest
Although mammals are found worldwide, they cluster most densely in warm, wet, topographically varied regions. The greatest concentrations of species occur in the Amazonian lowlands and Andes of northern South America, equatorial East Africa, and Southeast Asia. Central America also ranks among the richest zones. These areas combine tropical heat, heavy rainfall, and complex terrain, which together create many distinct micro-habitats packed into a small area.
When researchers mapped the top 2.5% of the planet by mammal richness, the hotspots collapsed into just two primary regions: Central America through northern South America, and equatorial Africa (especially the east). That concentration was surprisingly narrow. Topographic variety, meaning mountains, valleys, and varied elevations, appears especially important for species with small ranges, while overall plant productivity matters more for widespread species.
Tropical and Temperate Forests
Forests support more mammal species than any other single habitat type. Tropical rainforests in the Amazon, Congo Basin, and Southeast Asia are home to primates, big cats, tapirs, sloths, and thousands of rodent and bat species. The layered canopy structure gives mammals distinct vertical zones to exploit. Some never touch the ground: tree-dwelling primates, squirrels, and possums spend entire lives in the canopy, feeding on fruit, insects, and leaves.
Temperate forests in North America, Europe, and East Asia support a different but still diverse community. Deer, bears, wolves, foxes, raccoons, and dozens of small rodent species occupy these woodlands. Seasonal changes drive behavioral shifts like hibernation and migration that tropical forest mammals rarely need.
Bats and the Aerial World
Bats are the only mammals capable of true flight, and they account for roughly one in five mammal species. Their habitat needs revolve heavily around roosting sites. Most cavity- and bark-roosting bats rely on standing dead trees in intermediate stages of decay, sheltering under peeling bark, inside trunk crevices, or within hollowed-out cavities. Other species roost in caves, rock crevices, or even large leaves they fold into tents. A few species, like the southeastern myotis, roost exclusively inside cavities of living trees.
This dependence on specific roost structures means bat habitat quality often comes down to the availability of old, decaying trees or undisturbed cave systems rather than the broader landscape alone.
Oceans and Freshwater
Marine mammals, including whales, dolphins, seals, sea lions, and manatees, occupy every major ocean from the tropics to polar ice edges. Their range is shaped largely by temperature and prey availability. Dolphins, for example, use their thick blubber layer as a thermal buffer, storing heat for roughly an hour when moving from cooler open water into warmer coastal shallows. Species like the Hawaiian spinner dolphin rely on constant movement to generate enough body heat in waters near their lower temperature tolerance.
Seals and walruses split time between water and land or ice, hauling out to rest, breed, and nurse pups. River dolphins inhabit freshwater systems in South America and Asia, while otters occupy rivers, lakes, and coastal zones across multiple continents. Freshwater habitats also support hippos in Africa and the platypus in Australia.
Deserts and Arid Regions
Deserts seem inhospitable, yet mammals thrive in them worldwide. Kangaroo rats in North America, jerboas in Central Asia, and numerous rodent species across the deserts of South America have all evolved to survive where free water is scarce or nearly absent. South American desert rodents, once thought to rely mainly on behavioral tricks like nocturnal activity, actually possess structural and physiological systems for water conservation that rival those of the more famous kangaroo rats. Their kidneys can produce highly concentrated urine, and specialized water channels in their tissues minimize loss.
Larger desert mammals like camels, oryx, and fennec foxes use a combination of strategies: tolerating wide swings in body temperature, minimizing water loss through concentrated waste, and timing activity to cooler hours. Many desert mammals get most or all of their water from the food they eat rather than drinking.
Mountains and High Altitude
Some mammals live above 4,000 meters, where oxygen levels drop to roughly 60% of what’s available at sea level. The challenge is not just cold but the thin air. Andean camelids (llamas, vicuñas, alpacas, and guanacos) solve this with hemoglobin that binds oxygen more tightly than that of lowland relatives. The vicuña, which lives at the highest elevations, has an especially strong oxygen-binding adaptation due to additional changes in its blood proteins.
Yaks on the Tibetan Plateau inhabit elevations from 3,000 to 6,000 meters. They can activate a fetal form of hemoglobin with even higher oxygen affinity, a trait that helps both calves before birth and adults during extreme exertion. Pikas, snow leopards, Himalayan tahr, and several species of mountain goat round out the high-altitude mammal community, each with its own suite of thick insulation and metabolic adjustments.
Polar and Subpolar Regions
The Arctic supports polar bears, Arctic foxes, musk oxen, caribou, lemmings, and several seal species. Antarctica’s land is mammal-free, but its surrounding waters host leopard seals, Weddell seals, and massive whale populations that feed on krill. Polar mammals rely on seasonal changes in fur density, plumage (in the case of seals, blubber thickness), and circulatory tricks that cool their extremities to reduce heat loss from the warm core. Counter-current heat exchange in the blood vessels of flippers, legs, and tails lets Arctic and Antarctic species stand on ice or swim in near-freezing water without losing dangerous amounts of body heat.
Underground Burrows
A surprising number of mammals spend most of their lives underground. Moles, naked mole-rats, pocket gophers, and several species of golden mole rarely or never surface. Their burrows create remarkably stable microclimates. In one study of a burrowing mammal, winter outside temperatures swung from minus 18°C to over 23°C, while burrow temperatures stayed between minus 4°C and about 2°C. In summer, when surface temperatures exceeded 35°C, burrows averaged just 17.7°C.
That thermal buffering is the main advantage of underground life. It lets small mammals avoid both lethal cold and dangerous overheating without the metabolic cost of constant temperature regulation. The tradeoffs are low oxygen, elevated carbon dioxide, and total darkness, which have driven adaptations like reduced eyes, enhanced touch sensitivity, and tolerance for air that would leave surface mammals gasping.
Cities and Human Landscapes
Urbanization has created an entirely new mammal habitat. Raccoons, coyotes, red foxes, rats, mice, and many bat species now live at higher densities in cities than in surrounding wild areas. Research in the urban-to-rural landscape around Tianjin, China found that stray cat densities were roughly 14 times higher in urban areas (about 3.75 per square kilometer) than in exurban zones (0.26 per square kilometer). Dog densities followed the same pattern. Both species increased with urban development, driven by greater access to food and fewer natural competitors.
Wild species showed a more complicated response. Their densities depended on both urban factors and natural habitat variables like vegetation cover, meaning they don’t simply increase or decrease with development. Some wild mammals, like hedgehogs and weasels, persist in cities but at lower numbers. Others, like deer in parts of North America, have exploded in suburban areas where predators are absent and gardens provide easy food. The result is a reshuffled mammal community unlike anything found in purely wild landscapes.