Extinction
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Symbiosis is a noun. It refers to a relationship between living organisms of different species. The noun symbiote refers to an organism involved in a symbiotic relationship.
1. Alive 2. become extinct if suitable action to protect the species is not taken
A living fossil generally refers to a living organism, animal or plant, whose species has been around long enough on the planet to be part of the fossil record. Most fossilized species are extinct, but there are a few which are either still in existence, or have descendents which closely resemble them.
Co-habitation
Individuals of a species that live in an area are called population.
The only surviving hominid species today is Homo sapiens, which includes modern humans. Other hominid species, such as Neanderthals and Denisovans, are known to have existed in the past but are now extinct.
Fortunately, homo sapiens have not died out. That is because we ourselves are homo sapiens ("homo sapien" refers to the genus and species of humans-genus and species are simply terms used in "Taxonomy", that is, the classification of living things.)
Extinction refers to complete eradication of a species such as the Warrah or Dinosaurs (things that no longer exist), whereas an endangered species is merely under threat of eventual extinction, but is not there yet, like a panda or a California Condor.
If animals can breed and produce a viable (fertile) offspring they are termed a "species". Often two closely related species can inter-breed and produce an offspring that will be a non-viable (sterile) hybrid. An example of the later would be the cross-breeding of a horse with a donkey.This cross produces a "Mule", which is sterile & unable to reproduce.
A living fossil generally refers to a living organism, animal or plant, whose species has been around long enough on the planet to be part of the fossil record. Most fossilized species are extinct, but there are a few which are either still in existence, or have descendents which closely resemble them.
A single individual is not used to describe a population. A population refers to a group of individuals of the same species living in a particular area.