The top 10 most biodiverse countries

• Today (May 22) is World Biodiversity Day.
• In celebration, below is a look at the world’s ten most biodiverse countries as measured by species richness.
• This list takes a simplified approach, created a weighted index using five groups of animals — amphibians, birds, fish, mammals, and reptiles — and one group of plants — vascular plants.

Author’s note: after posting, I located a better data set on plant species diversity, which altered the original rankings dropping Peru from #4 to #6.

May 22 has been designated as the “International Day for Biological Diversity” by the United Nations to “increase understanding and awareness of biodiversity issues”. In celebration of World Biodiversity Day, below is a look at the world’s ten most biodiverse countries as measured by species richness.

A few caveats before we get to the list. There are many ways to measure biodiversity. This list takes a simplified approach, created a weighted index using five groups of animals — amphibians, birds, fish, mammals, and reptiles — and one group of plants — vascular plants. Each country is ranked by its percentage of species in each group relative to the total global number of species for each group. There are obviously major omissions: the system don’t account for insects and other invertebrates, fungi, microorganisms, and a number of other large groups of living creatures. Nor does it attempt to measure diversity of populations within species, levels of endemism, or intactness of ecosystems. Nonetheless we believe the list represents a fair proxy for the planet’s most biodiverse countries. Some of the countries in the ranking could move up or down a few places in the rankings depending on one’s data sources and methodology.

Just missing the top 10

Several countries — Bolivia, Democratic Republic of the Congo, South Africa, Malaysia, Vietnam, Papua New Guinea, Thailand, and Tanzania — narrowly missed the top 10. For some plant and animal groups, some of these countries do make their respective top 10s, including South Africa for vascular plants and Papua New Guinea for animals.

#10 (tie): United States and Venezuela

While they may be polar opposites in terms of current political ideology, Venezuela and the United States have at least one thing in common: incredibly high levels of biodiversity. Due to its diversity of freshwater and marine ecosystems, the United States ranks particularly high in terms of fish species, while Venezuela is one of the world’s most biodiverse countries when it comes to birds.

#9: Ecuador

Despite having a smaller land area than the state of Arizona, Ecuador outpaces the entire United States when it comes to biodiversity. The country — which spans the Andes-Amazon region and includes the Galapagos archipelago — outranks the U.S. in bird (1588 bird species in Ecuador versus the USA’s 844 species) and amphibian species (539 species versus 300 species).

#8: India

With a large landmass covering a range of ecosystems, India scores well across the board in terms of species richness. It ranks especially high when it comes to reptiles and birds. Some of India’s best known species are charismatic megafauna: elephants, rhinos, lions, and tigers.

#7: Australia

Australia really outperforms when it comes to reptiles and fish, leading the world in both categories according to The Reptile Database and FishBase. The Great Barrier Reef and terrestrial ecosystems ranging from dry deserts to tropical rainforests give the continent-nation a boost in the rankings.

#6: Peru

Unsurprisingly, three of the top six countries on this list are in South America, which is home of the world’s largest rainforest: the Amazon. Peru is second only to Colombia in terms of birds and ranks in the top five globally for amphibians, mammals, and plants.

#5: Mexico

Spanning Meso-American rainforests, dry forests, mountain habitats, and deserts, Mexico scores well across most plant and animal groups. Its strongest ranks come among birds, mammals, reptiles, and plants.

#4: China

While most Americans probably think of massive cities when someone mentions “China” or perhaps the panda bear, the giant East Asian country is actually home to a staggering array of habitats, from tropical rainforests in Yunnan to the Gobi desert. China ranks particularly well for birdlife, plants, and fish.

#3: Indonesia

An archipelago of more than 10,000 islands, Indonesia has a wide array of terrestrial and marine ecosystems, including parts of the world’s third largest rainforest and the famed Coral Triangle. Indonesia has the most mammal species of any country and is narrowly edged out by Australia when it comes to fish species, according to FishBase. It ranks fourth with 1615 bird species, according to BirdLife International. Indonesia is the only place on Earth where rhinos, orangutans, elephants, bears, and tigers can be found living in the same forest.

#2: Colombia

Colombia’s incredible bird, amphibian, and plant richness allow it to beat out Indonesia on our index. With 1826 species, Colombia has more species of birds than any country on Earth. Colombia’s biological richness is a product of its variety of ecosystems, including tropical forests in the Amazon and Choco, mountain habitats like the Sierra Nevada and Andes, the grasslands of the llanos and páramos, and islands like Gorgona in the Pacific and San Martin in the Caribbean.

#1: Brazil

Brazil is the Earth’s biodiversity champion. Between the Amazon rainforest and Mata Atlantica forest, the woody savana-like cerrado, the massive inland swamp known as the Pantanal, and a range of other terrestrial and aquatic ecosystems, Brazil leads the world in plant and amphibian species counts. It ranks second in mammals and amphibians, third in birds, reptiles and fish.

Small Countries: Pockets of Biodiversity

This list focused on total biodiversity. It is therefore biased toward big countries like Brazil, the U.S., Russia, and China. But on a per unit of area basis, tiny tropical countries are biodiversity champions: Brunei, The Gambia, Belize, Jamaica, El Salvador, Costa Rica, Rwanda, Equatorial Guinea, and Panama top the list.

Disagree with our ranking? Feel free to comment below.

DATA SOURCES: AmphibiaWeb, FishBase, IUCN Red List, Reptile Database, Birdlife International, Mongabay.com, and UNEP-WCMC (World Conservation Monitoring Centre).

Update: 5/23/2016: Readers have asked what countries were included in the assessment. Here is the full list — we were limited by time and data availability: Algeria, Angola, Argentina, Australia, Azerbaijan, Bangladesh, Belize, Benin, Bhutan, Bolivia, Brazil, Brunei, Cambodia, Cameroon, Canada, Central African Republic, Chile, China, Colombia, Congo, Costa Rica, Croatia, Cuba, Dominican Republic, DR Congo, Ecuador, El Salvador, Equatorial Guinea, Ethiopia, France, French Guiana, Gabon, Gambia, Georgia, Ghana, Greece, Guatemala, Guinea, Guinea-Bissau, Guyana, Haiti, Honduras, India, Indonesia, Iran, Italy, Ivory Coast (Cote d’Ivoire), Jamaica, Japan, Kazakhstan, Kenya, Kyrgyzstan, Laos, Liberia, Madagascar, Malawi, Malaysia, Mali, Mexico, Morocco, Mozambique, Myanmar (Burma), Nepal, New Zealand, Nicaragua, Nigeria, Pakistan, Palau, Panama, Papua New Guinea, Paraguay, Peru, Philippines, Portugal, Russia, Rwanda, Senegal, Serbia, Seychelles , Sierra Leone, Singapore, Solomon Islands, Somalia, South Africa, Spain, Sri Lanka, Sudan, Suriname, Tajikistan, Tanzania, Thailand, Togo, Trinidad-and-Tobago, Turkey, Uganda, Ukraine, United States, Uzbekistan, Venezuela, Viet Nam, Zambia, and Zimbabwe.