Why is preventing the introduction of invasive species considered more effective than removing established invaders?

Preventing the introduction of invasive species is widely considered the most effective strategy for protecting biodiversity because managing established populations is often prohibitively expensive and logistically difficult.12

Once a nonnative species becomes established, eradication efforts can take decades, as seen in the 19-year program required to remove cats from Marion Island. Furthermore, attempting to control established invaders through biological control—such as introducing a second nonnative species to manage the first—carries significant ecological risks, including the potential for the control agent to harm native species.2

In contrast, proactive measures—such as inspecting international shipping materials for "stowaway" organisms and enforcing strict regulations on the pet trade—address the problem at its source. By stopping the arrival of these organisms, governments and citizens can prevent the ecosystem disruption, biodiversity loss, and economic damage that occur once an invasive species gains a foothold in a new environment.13