The question of which place on Earth has the most animals is complex because “most” can refer to the total number of individual creatures or the greatest variety of distinct life forms. Scientists prioritize the latter measure, known as species richness, when determining the planet’s most biologically significant locations. Species richness is a simple count of the number of different types of species within a defined area. Identifying locations with the highest species richness reveals the global centers of life where the evolutionary process has yielded the greatest number of unique species.
Species Richness Versus Population Density
To understand where the “most animals” are found, it is necessary to distinguish between species richness and population density. Population density, or biomass, measures the total number or weight of individual organisms present in a given space. For instance, a square meter of Antarctic krill swarm or an African savanna with millions of migratory wildebeest might have the highest population density.
Species richness focuses on the sheer count of unique species, regardless of individual numbers. Ecologists consider this a more informative measure of an ecosystem’s health and evolutionary output. High species richness indicates a habitat that has fostered a wide array of life, often including many species found nowhere else on Earth. This analysis uses species richness as the primary determinant for locating the planet’s richest animal habitats.
The Reigning Champions: Terrestrial Biodiversity Hotspots
The terrestrial champions of species richness are the tropical rainforests, particularly the Amazon Basin in South America. The Amazon is estimated to house at least 10% of the world’s known biodiversity, a staggering concentration of life forms. This immense area contains approximately 40,000 plant species, which in turn support a complex web of animal life. The Amazon River system alone is home to over 2,200 known species of fish, making it the most diverse river on Earth.
Conservation science defines “Biodiversity Hotspots” as regions exceptionally rich in species and under severe threat. The 36 globally recognized hotspots cover only 2.5% of the Earth’s land surface but contain over half of the world’s endemic plant species. Beyond the Amazon, the Congo Basin in Central Africa is the second-largest rainforest and a major biodiversity center. Regions like the Tropical Andes also amplify terrestrial diversity, though the true species count, especially insects, is likely far higher than current estimates.
The Marine Realm: Coral Reefs and Ocean Diversity
In the marine environment, the equivalent of the tropical rainforest is the coral reef, with the Coral Triangle recognized as the global epicenter of ocean diversity. This vast, roughly triangular area spans 5.7 million square kilometers across the tropical waters of Southeast Asia. Though covering only a small fraction of the world’s oceans, the Coral Triangle contains more than 76% of the world’s known shallow-water reef-building coral species.
This region is often called the “Amazon of the seas” due to its unparalleled species density. It is home to over 2,200 species of reef fish, representing 37% of the world’s total reef fish species. The highest concentration of this marine life is found around the Bird’s Head Seascape of Indonesian Papua. While other ocean zones may contain a greater total biomass, no other marine area approaches the Coral Triangle’s species richness.
Environmental Factors Driving High Biodiversity
The identified locations, such as the Amazon or the Coral Triangle, share specific environmental conditions that drive their exceptional species richness. High solar energy input is a fundamental factor, providing the energy for high primary productivity—the massive growth of plants and algae at the bottom of the food chain. This abundance of resources allows a larger number of species to coexist and thrive.
Climate stability is another powerful driver, particularly the lack of major disruptions like glaciation or extreme temperature swings over long geological timescales. This extended period of stable conditions has allowed evolutionary processes to proceed largely uninterrupted, giving species more time to diversify. The consistent warmth and rainfall in tropical areas facilitate year-round growth and reproduction, speeding up the generation of new life forms.
Geographical complexity also plays a decisive role in generating high species richness through habitat heterogeneity. The rugged topography of mountainous regions, the varied depths of the ocean floor, or the intricate structure of a coral reef create a multitude of distinct ecological niches. These diverse microhabitats allow many specialized species to occupy close proximity without competing directly, resulting in the variety of life seen in Earth’s biodiversity hotspots.