Functional extinction is a term that is used to describe a certain type of extinction. Certain factors must take place in order for the species of animals can be described as functional extinction. These factors include that the animal does not even have any fossils left. They do not contribute to the ecosystem or food chain based on the population that is still left on the Earth.
Next, the population of this animal species is not reproducing and is not showing signs of growing. Some of these animals that fall under the category of functional extinction include the South China tiger, Ivory-billed woodpecker, Christmas Island forest skink, Christmas Island shrew, Baiji dolphin, Pinta Island tortoise, Christmas Island pipistrelle and the Northern White rhino.
Functional extinction does not mean a species is completely extinct. It actually means that a species is no longer viable in the wild or that the population is so small it is no longer significant in the ecosystem. Basically, this happens when species still technically exists but circumstances make it impossible for them to maintain notable population numbers.
Functional extinction can also can be related to the food chain—if an animal's food source goes extinct, they won't be far behind it due to starvation. Numerical extinction the term that most people think of when they hear "extinction" in that there are no more of that particular species on the Earth.