Les invasions biologiques : une menace pour les écosystèmes et pour nos sociétés

Summary

Biological invasions are a major, relatively under-recognized cause of biodiversity loss. They occur when human activities transport species beyond their native ranges and those species establish and spread in new ecosystems. Invasive alien species include plants, animals, and microorganisms in terrestrial, freshwater, and marine environments.

By 2023, more than 37,000 alien species had been recorded worldwide, with at least 3,500 classified as invasive. Examples include Asian hornets, tiger mosquitoes, Japanese knotweed, and red-eared sliders, along with many other species introduced around the world.

Invasions are more likely to succeed when conditions suit the newcomer and it lacks the predators, competitors, parasites, or herbivores that constrain it in its native range. Local species may also be poorly adapted to unfamiliar competitors or predators. Together, these factors can allow invaders to grow rapidly and disrupt ecosystems. One cited comparison found that introduced large herbivores in Australia—such as goats, horses, and camels—have a combined biomass two to three times that of native large herbivores, such as kangaroos.

Impacts vary by species and ecosystem and can include:

• Decline or extinction of native species and destruction of habitats.
• Disruption of ecosystem functions and services, including pollination, seed dispersal, and nutrient recycling.
• Changes to soil and water quality, and increases in the frequency or severity of fires.
• Economic and social costs, including agricultural losses, infrastructure damage, and healthcare costs from allergies or diseases transmitted by invasive mosquitoes. Estimated economic losses are described as being on the same order of magnitude as those caused by natural disasters.

Management approaches

• Prevent introductions at their source: Biosecurity measures, such as quarantining containers and inspecting high-risk cargo, are presented as the most effective and least costly approach.
• Limit spread: Control species that are already established but have not yet spread to additional areas.
• Eradicate where feasible: Remove invasive species from vulnerable places, such as fragile islands.
• Act early: A mathematical model using mosquito invasion data found that delaying control can increase program costs by tens of millions of euros per year.

The number of invasions is expected to continue growing. Increasing international trade and travel create more opportunities for species to be transported, while climate change—especially warmer winters—allows more introduced species to survive and establish in regions that were previously unsuitable. Models project that the accelerating growth in invasions will continue.

The video nevertheless argues that progress in prevention and control offers grounds for optimism, provided scientists, biodiversity managers, authorities, and citizens recognize the scale of the issue.

Researchers and sources mentioned

• Franck Courchamp, CNRS research director, identified in the video metadata.
• An unnamed study comparing the biomass of introduced and native large herbivores in Australia.
• An unnamed mathematical-modeling study combining ecology and economics and using mosquito invasion data to estimate the costs of delaying control.
• A 2023 global tally of alien and invasive species; no source or author is named in the subtitles.