Causes of Extinction

Humans have played a significant role in the extinction of species prior to historic times but the true extent of such anthropogenic impacts during the Holocene (the last 11,000 years) remains unclear. However, after 1500 AD it is clear that humans are responsible for most recorded extinctions. The exact causes of most extinctions are poorly documented, but invasive alien species, habitat loss, and overexploitation have all been major factors. Even when species are relatively well studied it is often difficult to identify the main cause of extinction as most species are threatened by more than one process and these often interact in unpredictable ways. Furthermore, the threat process that causes a species to become susceptible to extinction (such as habitat loss) may be very different to the final process that drives it to extinction (such as a hurricane).

Relatively good data exist for birds indicating that the impacts of invasive alien species, overexploitation by humans, and habitat destruction and degradation have been the major causes of extinctions, with invasive species being associated with the  extinction of at least 65 species. Predation by introduced dogs, pigs and mongooses, and habitat destruction by sheep, rabbits and goats have been implicated in the extinctions of some of these species. However, it is predation by introduced rats and cats, and diseases caused by introduced pathogens that have been the most deadly overall, contributing to the extinction of some 30, 20 and 10 species respectively. Almost all the factors that have led to the extinction of species in the modern era continue to operate, many with ever-increasing intensity. 

Major threats to ecosystems and biological diversity (biodiversity) are: