There are many plant and animal species that are in immediate danger of extinction.
However, there are several degrees of endangerment that have been defined.
Critically endangered species
This group includes species that probably cannot survive without direct human intervention (e.g. the California condor).
Threatened species
This group includes species which are abundant in parts of their range but are declining in total numbers (e.g. the grizzly bear).
Rare species
Species in this group exist in relatively low numbers over their ranges but are not necessarily in immediate danger of extinction (e.g. the greater prairie chicken)
What is Extinction?
Extinction is, in fact, a normal process in the course of evolution. Throughout time, many more species have become extinct than exist today. In general, species have slowly disappeared because of climatic changes and the inability to adapt to such conditions as competition and predation.
Why is Extinction Increasing?
Since the 1600s, the process of extinction has accelerated rapidly due to the impact of both human population growth and technological advances on natural ecosystems. Today the majority of the world's environments are changing faster than the ability of most species to adapt to such changes through natural selection.