A species is one of the basic units of biological classification. A species can be loosely defined as a group of individual organisms that have very similar appearance, anatomy, physiology and genetics.

Types of species

A species can be a mammal, a tree, a coral, a fungus, an insect, a sponge or any one of a number of life forms.

They can be found in near-to boiling water, sulphurous sludge, frozen wastelands, underground rivers, spiny forests, perilous cliffs or living almost all their life in mid-air.

  • Together we and they make up life on this planet.
  • And altogether we call this range and breadth of life 'biodiversity'.
  • WWF's mission is make sure we don't lose this marvellous array of life, this biodiversity.

How much diversity of life is on this Earth?

According to the IUCN (International Union for the Conservation of Nature), humans know about an estimated 1,562,663 different life forms on this planet.  This includes:

  • 5,416 mammals
  • 16,000 mushrooms or fungi
  • 29,300 fish
  • 950,000 insects
  • 287,655 plants

Many experts feel we have still to discover many, many more species - some estimates say we have yet to discover and describe millions of 'new' lifeforms.

Of the 1.5 million species, what needs saving?

The IUCN maintains the red list, which lists 16,118 endangered species.

What does Endangered mean?

Officially, threatened species are those listed as Critically Endangered (CR), Endangered (EN) or Vulnerable (VU).

Practically this means:

  • Critically Endangered (CR): A species facing an extremely high risk of extinction in the wild.
  • Endangered (EN): A species considered to be facing a very high risk of extinction in the wild.
  • Vulnerable (VU): A species considered to be facing a high risk of extinction in the wild.

More on the IUCN Category listings.

How WWF categorizes the species it works on.

Diagram showing the species groups (kingdom, phylum, order, family, genus, species) and how this ... 
How the species tree maps to real life... aka a Bengal tiger.

The Red List

The Red List is the world's most comprehensive inventory on the global conservation status of plants and animals. 

Every 5 years the IUCN evaluates the population status of each species and the threats to each one's survival.

Based on that information the IUCN assigns each species a category. These categories are:

  • Extinct
  • Extinct in the Wild
  • Critically Endangered
  • Endangered
  • Vulnerable
  • Threatened
  • Near Threatened
  • Least Concern
  • Domesticated