Study led by the University of Fribourg corrects previous assumptions about invasive species and points the way towards a new international environmental policy to reduce species extinctions

Invasive alien species are one of the main drivers of species extinctions worldwide. However, previous global estimates of the geographical distribution of this biodiversity loss were subject to systematic research bias. Since far more research is conducted and documented in the countries of the Global North, i.e. in North America and Europe, that is where the highest figures on invasive species appear, and consequently there is also the greatest number of impact reports. Now, a new study led by Sven Bacher, titular professor of Applied Ecology at the University of Fribourg, has shown that in countries of the Global South, invasive species are causing significantly higher environmental damage than in the Global North. This is due to a combination of rapid economic growth and weak state governance. The study, which also involved researchers from Germany and the Czech Republic, was published in the journal Science.

Measuring damage instead of counting species
The international research team led by Prof. tit. Sven Bacher, Prof. Petr Pyšek (Czech Academy of Sciences) and Prof. Hanno Seebens (University of Giessen, Germany) applied a new methodological approach: instead of simply counting the presence of invasive species, the scientists developed a new metric: «average impact severity». This metric places the number of severe impacts – such as local eradication of native populations – in relation to all reported local environmental impacts and is consequently free from research bias. The work is based on the new Global Impacts Dataset of Invasive Alien Species (GIDIAS), the creation of which was also coordinated by the University of Fribourg. It encompasses more than 22,000 documented impacts of invasive species in 172 countries.

The result is a scientific correction of previous assumptions about the consequences of invasive species. While the absolute number of documented species and reports is high in the Global North, the relative severity of impacts is considerably higher in the Global South. «That can be seen even in individual species,» explains Bacher, the study’s lead author. «Invasive species that cause environmental damage both in the Global South and in the Global North do 50% more harm in countries of the Global South compared to those of the Global North. Especially in the emerging economies of South America, Africa and Asia, invasions result more frequently in catastrophic environmental impacts.»

Emerging economies particularly hard hit
The study also provides an explanation for this phenomenon that affects emerging economies particularly severely. These countries have high economic growth and an intensive engagement in global trade, which greatly accelerates the inflow of new invasive species. At the same time, they often have less developed state structures, higher corruption rates and lower capacity for managing biological invasions.

«Although countries of the Global North have numerous invasive species, intensive management of the ecosystems there prevents any massive impact,» says Seebens. «By contrast, the rapid economic growth of emerging economies is accelerating the introduction of invasive species, while their institutional capacity to react is lagging behind.» Using complex statistical models, the study shows that good governance and proactive management can effectively reduce the impact of biological invasions. These mechanisms are frequently lacking in countries of the Global South, which means that invasive species are able to cause catastrophic environmental damage unhindered.

Consequences for international environmental policy
The study’s findings have far-reaching consequences for international environmental policy. «Prevention is the most efficient way of preventing the impact of invasive species, but that requires effective management structures in every country and strong international cooperation,» underscores Bacher. «If we want to overcome the global biodiversity crisis, we have to close the management gap between North and South and stop marginalising the regions most severely affected by invasive species.» The researchers point out that monitoring the global spread of species is not enough. «We must not allow the environmental damage in regions of the Global South – many of which are home to the greatest biodiversity – to become irreversible,» says Prof. Seebens.

- Publication: «Invasive species’ environmental impacts are more severe in the Global South», Science, vol 393, issue 6809, pp. 376-380, DOI: 10.1126/science.aed0603