What is the term used to describe the phenomenon where the extinction of one species leads to the extinction of another species associated with it in an obligatory way?

Co-extinction

The correct answer is Option (3) – Co-extinction

The term used to describe the phenomenon where the extinction of one species leads to the extinction of another species associated with it in an obligatory way is "Co-extinction." Co-extinction occurs when two or more species have a dependent relationship, and the extinction of one species directly or indirectly causes the extinction of the other species.

This phenomenon is often observed in cases of mutualistic interactions, where two species rely on each other for survival or reproduction. For example, if a plant species depends on a specific pollinator for successful reproduction, and the pollinator species goes extinct, the plant species may also face extinction since it cannot reproduce without the pollinator's assistance. Similarly, if a host species goes extinct, the parasites or other species that depend on it for survival may also become extinct.

Co-extinctions can have cascading effects on entire ecosystems, leading to the loss of multiple species and disrupting ecological interactions. It highlights the interconnected nature of biodiversity and the importance of protecting not only individual species but also their associated species and habitats to ensure the stability and resilience of ecosystems.