What is the definition of extinction in the context of speciation?

Extinction, in the context of speciation, refers to the permanent loss of a species when no individuals of that species remain alive anywhere on Earth. This means that once a species goes extinct, it can no longer reproduce or contribute to the biodiversity of an ecosystem. Extinction can result from various factors, including habitat loss, environmental changes, competition, and changes in climate.

Understanding this definition is crucial because it highlights the finality of extinction compared to other concepts, such as adaptation or temporary population fluctuations. For example, adaptation involves changes within a species as it evolves to better survive in its environment, while temporary disappearance might imply that a species could reappear or recover under certain circumstances. Similarly, a decrease in population size does not necessarily mean that a species is extinct, as populations can fluctuate or recover over time. Thus, the enduring nature of extinction distinguishes it from these other biological concepts.