Invasive species threaten biodiversity

Leading international experts have estimated that even moderate increases in the spread of invasive plant and animal species will cause major damage to ecosystems and biodiversity around the world.

This has important ramifications for human livelihoods too, according to the 38 scientists who published their assessment in the journal Global Change Biology.

They found the biggest drivers of invasive species across different ecological and social contexts are global transport of goods, climate change and economic development such as land use and energy consumption.

Others include tourism, recreation, population changes, migration and pollution.

Such human activities are spreading non-native species around the planet at an alarming rate. “We know from a range of recent studies that numbers and impacts of invasive species are increasing rapidly,” says first author Franz Essl, from the University of Vienna in Austria.

These ill-fated invaders can disrupt the delicate balance and stability of ecosystems, often with devastating consequences, if they thrive in their new environment.

Rabbits, for instance, pose a risk to threatened species around the world by destroying plants, competing with native animals for food, eroding soil and helping predators to thrive.

Invasive species can have major economic impacts. In Africa, for instance, the non-native fall armyworm moth decimates crops worth billions of dollars, while in Asia the common rice black bug can ruin up to a third of rice crops.

Freshwater zebra mussels (Dreissena polymorpha) cost North America more than a billion dollars each year. They stick to hard surfaces including boat motors, water treatment pipes and turtle shells, their sharp shells can impact tourism and they have ecological impacts on native mollusc and fish populations.

In Australia, scientists say alien species pose a bigger threat to biodiversity than anything else, including climate change, a problem faced by islands and isolated continents that Essl and colleagues predict will proliferate to other regions in the future.

But while their current effects are well known, it’s difficult to predict their future spread and consequences, prompting Essl and colleague Bernd Lenzner to conduct the expert assessment using standardised surveys, bringing together scientists from Europe, North and South America, the Pacific Islands, Australia, Africa and Asia.

The survey aimed to establish the impacts of alien species in different environmental, climatic and socioeconomic contexts, contrasting best-case (human societies act decisively to stop invasions) and worst-case scenarios (business as usual).

Even with resolute action, they estimated that a 20% to 30% increase in newly introduced species is enough to severely impact biodiversity, although the impacts are more diverse than they would be with no action, pointing to opportunities for intervention.

If things continue without action, all drivers would have a significant impact, and most experts considered they could pass the point of no return for ecosystem biodiversity.

Impacts differed according to region; for instance, climate change favours the establishment of alien species in polar and tropical regions while tourism and increased human population density are major drivers in tropical and subtropical environments.

The authors say their study will help inform priorities for the Post-2020 Framework of the Convention on Biological Diversity and the United Nations 2030 Agenda for Sustainable Development, underscoring the urgency for action.

“It is essential to address the causes of biological invasions,” says Essl. This includes improving legislation such as biosecurity, establishing response capacities to rapidly manage intrusions, and increasing public awareness.