Much of the Earth's species diversity is concentrated into a few relatively small areas. Twenty-five regions have been identified which together cover only 1.4% of the Earth's land surface but contain nearly half of all plant species and a third of all terrestrial vertebrate species. All are under pressure from human activities.

BBC News Online looks at range of biodiversity hotspots.

California Floristic Province

California's extensive area and great diversity of habitats means it has a very large range of animal and plant species, which includes the world's largest redwood trees.

The California Floristic Province covers 70% of the state and spreads into Oregon and northern Mexico. It is one of the few Mediterranean-type climates in the world and is home to populations of the California condor, the giant salamander and the mountain lion.

Over 2,000 of the plant species that grow in the province occur nowhere else in the world. But urban and agricultural development is eating into the area, especially along the central and southern coasts of California.

At present, 9.7% of the total land area of the California Floristic Province is protected. It contains 12 threatened species and two endangered ones.

Central America

The forests of central America contain a wealth of species, including jaguar, sloths, morpho butterflies and 24,000 plant species.

Mexico is trying to protect monarch butterflies

The region is also a vital migration corridor for many birds, and Mexico is the wintering ground of the endangered monarch butterfly, which flies from North America to Mexico's oyamel fir forests.

Today, only about 20% (231,000 sq km) of the original forests remain in a relatively natural state - and those are under threat.

Some conservation efforts are under way, however. The Mexican authorities are cracking down on illegal logging in the hope of protecting the millions of migrating butterflies.

Caucasus

The Caucasus hotspot covers an area of over 500,000 sq km between the Caspian Sea and the Black Sea, and includes parts of Georgia, Armenia, Azerbaijan, Russia, Iran and Turkey.

It contains more than twice the animal diversity found in adjacent areas in Europe and Asia.

The conservation organisation WWF has named the Caucasus as a large herbivore hotspot. Eleven species of large herbivore, as well as five species of large carnivore, are found over a relatively small area.

Conservation is problematic in the region because the hotspot straddles so many nations.

Polynesia and Micronesia

Polynesia and Micronesia represent over 1,000 islands scattered across 21.6 million sq km of the southern Pacific Ocean.

The region includes ecosystems ranging from lush forests to mangroves and savannahs. High levels of species diversity exist because of the way species have evolved in isolation from each other on different islands.

But the isolated island habitats mean species are less resistant to introduced predators and other human pressures. Human occupation in the last 200 years has seen 22 bird species become extinct.

Among the 88 threatened species are the Hawaiian crow, the Samoa flying fox and the Fijian ground frog.

Atlantic Forest, Brazil

The Atlantic Forest is less well known than the Amazon rainforest but it, too, is a hot-spot for biodiversity.

The forest makes up 13% of Brazil's territory and is the third largest major vegetation formation in the country after Amazonia and the Cerrado (an area of woodland savannah in north-east Brazil). Many of the species found there are unique. Seventy-two of the 620 bird species are thought to be endemic; 60 of 2,000 reptiles, 253 of 280 amphibians and 160 of 261 mammals.

There is great concern about the golden lion tamarin

But the Atlantic Forest, shrinking due to deforestation, is now less than 10% of its original size and many of its species are becoming endangered.

Primates are particularly affected - they represent nine of the 10 critically endangered mammals found in the Atlantic Forest. There is also great concern about the golden lion tamarin, whose numbers in the wild are estimated at around 500.

East Africa

Much of East Africa's biodiversity is concentrated in the Eastern Arc mountains and coastal forests of Tanzania and Kenya.

The Eastern Arc mountain chain is a series of heavily forested isolated peaks, where there are 1,500 plant species and 50 endemic reptiles.

Because of this density of species, the region is thought to be the hotspot in the world most likely to suffer the greatest plant and vertebrate extinction.

Agriculture and the encroachment of human development, along with logging, are the greatest threats to biodiversity in the region. Several species of colobus monkey are endangered along with three species of sunbird. Only about 2,000 sq km or 6.7% of the original hotspot remains unspoiled.

Madagascar

Madagascar and the Indian Ocean islands pack a great deal of biodiversity into a relatively small area.

Deforestation is putting many species under strain in Madagascar

But deforestation is putting many species under great strain. Madagascar is thought to have more critically endangered and endangered primates than anywhere else in the world.

The island has lost about 90% of its original vegetation, placing many species in great danger.

Western Ghats, India

The Western Ghats are a mountain range that runs along the western coast of India. The mountains cover an area of about 160,000 sq km stretching from the country's southern tip to Gujarat in the north.

Of the 372 species of mammal found in India, 63 are in the Western Ghats. Sixteen of these are endemic.

Faced with enormous population pressure, the lush mountains are at risk of a biodiversity crisis. Important populations of Asian elephants, Indian tigers, and the endangered lion-tailed macaque are threatened as agriculture and logging intensify.

Indonesia

Indonesia has around 500 species of mammal, which is second only to Brazil.

Indonesia has around 500 species of mammals

It is also in the world's top five countries for plant diversity, with an estimated 38,000 higher plant species. But illegal or uncontrolled logging is sweeping across the country creating a possible extinction crisis.

Critically endangered animals include the Javan rhinoceros, the Sumatran orang-utan and the silvery gibbon, which is endemic to Indonesia.

Although Indonesia has been criticised for excessive logging, timber is a major source of revenue and supports millions of people.

South-west Australia

The native forests of south-west Australia retain only 10% of their original 310,000 sq km of vegetation and yet they contain over 5,000 plant species and nearly 500 vertebrate species.

Despite early deforestation, the remaining forests are now well protected.

Amongst the unique creatures living in the area is the swamp turtle, which is thought to be the most threatened fresh water turtle in the world. The hotspot is also home to the honey-possum and the red-capped parrot.