Among ‘The Evil Quartet’, which one is considered the most important cause driving extinction of species?

The Evil Quartet, also known as the Four Horsemen of the Ecological Apocalypse, refers to the four primary factors that signifi cantly contribute to species extinction. These factors are: 
1. Habitat loss and fragmentation 
2. Alien species invasions 
3. Overexploitation 
4. Coextinctions 
Among these, habitat loss and fragmentation are considered the most important cause.
The destruction, degradation, or fragmentation of natural habitats is a major driver of species extinction. Human activities, such as deforestation, urbanisation, and land conversion for agriculture or infrastructure development, lead to the loss and fragmentation of habitats.
The destruction and fragmentation of habitats directly impact species’ survival by reducing available space and resources, disrupting ecological interactions, and limiting the ability of species to adapt and persist in their environments.
(1) Coextinction refers to the extinction of a species due to the loss of its dependent species. Some species have specialized relationships with other species, such as mutualistic or symbiotic interactions. If the species they depend on goes extinct, the dependent species may also face extinction. 
(3) Over exploitation occurs when species are harvested or hunted at unsustainable rates. This includes activities such as overfishing, illegal wildlife trade and excessive hunting. Over exploitation can lead to the decline and eventual extinction of targeted species, disrupting ecological balance and affecting biodiversity. 
(4) Alien species, also known as invasive species, are non-native species introduced to ecosystems. They can experience explosive population growth due to the absence of natural predators. Invasive species can out compete native species for resources, prey on native species, alter ecosystem dynamics and cause local extinctions.