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Why is preventing the introduction of invasive species often more effective than removing them later?

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wetland restoration — ecological restoration Wetland restoration along the Târnava Mică (Tîrnava Mică) River in Romania. A former gravel mine (left) was transformed into a functional wetland (right).

Preventing the introduction of invasive species is widely considered the most effective strategy for protecting biodiversity because eradication efforts are often prohibitively expensive, time-consuming, and complex.12

Once an invasive species becomes established, removing it requires intensive, long-term intervention. For example, eradicating a population of feral cats on Marion Island took 19 years of sustained effort. Furthermore, control measures for widespread invaders, such as the use of herbicides or biological control agents, carry significant risks. Introducing a nonnative predator or insect to manage an existing invader can lead to unintended consequences, such as the new agent harming native species.2

By contrast, prevention—through measures like stricter inspections at ports and international shipping hubs—stops the ecological disruption before it begins. Because invasive species can cause localized extinction of native organisms and permanently alter ecosystems, proactive prevention is ethically and practically superior to the difficult, uncertain, and costly process of attempting to restore a habitat after it has been compromised.132