New study: Invasive Species Cause Significantly Greater Damage in the Global South

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Invasive alien species are considered one of the most important drivers of global biodiversity loss. Yet the regions for which particularly large numbers of scientific reports are available are not necessarily those where invasive species cause the most severe ecological damage. The journal Science published a study showing that many countries in the Global South are considerably more affected than previous research suggested.

This distorted picture is primarily due to the uneven distribution of scientific research. Invasive species are studied far more intensively in Europe, North America, and other affluent regions. Consequently, there are more than twice as many reports from the Global North on their ecological impacts. This larger volume of data says more about the intensity of research than about the actual extent of the damage.

The example of Germany illustrates how extensively biological invasions are documented in the Global North. An inventory published in 2025 recorded 1,962 permanently established alien species in the country. Not all of them are considered invasive, as harmful effects have not been demonstrated for many. The large number of documented species is therefore not evidence that the ecological consequences are more severe in Germany than in less-studied regions.

To account for this research bias in global comparisons, Sven Bacher, Petr Pyšek, and Hanno Seebens examined the documented impacts of invasive species in 172 countries. Their analysis was based on the Global Impacts Dataset of Invasive Alien Species (GIDIAS). The database contains 22,865 entries on the impacts of 3,353 invasive species, compiled from more than 6,700 scientific and other specialist sources. It covers plants, vertebrates, invertebrates, and microorganisms in terrestrial, freshwater, and marine ecosystems.

Key findings

• More than twice as many reports on ecological impacts were available for the Global North.
• Nevertheless, the average severity of damage was 34% higher in the Global South.
• When the researchers considered only species whose impacts had been documented in both the Global North and the Global South, the same invasive species caused impacts that were, on average, 50% more severe in the South.
• The impacts were particularly severe in large emerging economies such as Brazil, India, and South Africa.

The figures of 34% and 50% refer to two different analyses. The 34% figure describes the comparison across all cases examined. The 50% figure results from the more direct comparison of invasive species found in both the Global North and the Global South. This comparison suggests that the differences are not solely due to different species having been studied in the two regions.

What matters is not the number of reports, but the severity of the consequences

Until now, the global scale of biological invasions has often been assessed using indirect measures, such as the number of alien species recorded or a country’s international trade volume. The number of documented ecological impacts is also unevenly distributed: Europe, North America, and other regions of the Global North have far more studies and damage reports than many countries in the Global South. As a result, well-studied countries inevitably appear more affected in absolute comparisons. However, a large number of documented impacts does not necessarily mean that the individual impacts there are also more severe.

To reduce the influence of this research bias, the scientists developed a metric called average impact severity. It measures the number of particularly severe impacts in relation to all documented local impacts of invasive species in a country.

Severe impacts include, for example, those in which the population of a native species declines substantially or disappears entirely at the local level. This allows a country with many documented but predominantly minor impacts to be compared with a less-studied country where a larger proportion of the known cases had serious consequences.

However, the metric cannot eliminate existing knowledge gaps, because where invasive species are rarely studied, even severe impacts may remain undetected. Moreover, results from countries with only a few documented cases are inevitably more uncertain. The new method therefore makes the comparison less dependent on the sheer volume of research, but it cannot replace missing data.

Another study from 2026 illustrates the extent of these knowledge gaps: The exact causes are known for only about a quarter of documented extinction events. The data are particularly incomplete for invertebrates and in tropical regions—precisely where a large proportion of the world’s biodiversity is found.

Particularly at risk: rapidly growing emerging economies

The researchers found the most severe impacts of invasive species not in the poorest countries, but primarily in rapidly growing economies in South America, Africa, and Asia. This pattern was especially pronounced in Brazil, India, and South Africa.

As economies grow, international trade, the movement of goods, and the number of imports often increase as well. This raises the risk that animals, plants, fungi, or pathogens will be unintentionally transported to new regions, for example in shipping containers, with plant shipments, on ship hulls, or in ballast water. Other species are introduced deliberately, for example for farming, as ornamental species, or for aquaculture.

Affluent industrialized countries also introduce numerous alien species through international trade. However, the Global North often has an institutional advantage: More capable authorities, greater management capacity, and lower levels of corruption on average increase the likelihood that new invasions will be detected early and countermeasures implemented consistently.

In many rapidly growing emerging economies, by contrast, introduction pressure is increasing faster than the capacity for monitoring, prevention, and control. The problem is therefore not economic growth itself, but the imbalance between the growing movement of goods and limited government capacity. This allows introduced species to establish and spread more easily before effective measures are taken.

Accordingly, the study’s statistical models show that good governance and preventive management were associated with lower average impact severity. However, they do not demonstrate a simple cause-and-effect relationship for every individual country. In addition to government structures, many other ecological, economic, and geographic factors can influence the scale of a biological invasion.

Water hyacinth and Nile perch: Two particularly consequential invasions

The water hyacinth (Pontederia crassipes) demonstrates how profoundly invasive species can alter an ecosystem. This floating plant, native to South America, reproduces very rapidly in warm, nutrient-rich waters and forms dense, almost continuous mats of vegetation. In South Africa’s Kruger National Park, it overruns watering holes, harming hippopotamuses, fish, and other native species. The floating mats block sunlight, displace native aquatic plants, and can severely reduce oxygen levels in the water.

The water hyacinth also spread massively across East Africa’s Lake Victoria within just a few years. By the mid-1990s, around 80% of Uganda’s shoreline was affected, and the covered surface area was estimated at approximately 4,000 hectares. The mats of vegetation altered habitats while also obstructing fishing, shipping, and access to the lake.

The water hyacinth reached Africa because it was cultivated as an ornamental plant for its striking purple flowers. It was able to escape from gardens and artificial ponds into natural bodies of water. It probably reached Lake Victoria through the Kagera River system. It is impossible to reconstruct with certainty where its spread within the catchment began.

Even better known are the ecological consequences of introducing the Nile perch (Lates niloticus) into Lake Victoria. The predatory fish, which in exceptional cases can grow up to two meters long and weigh around 200 kilograms, was deliberately released beginning in the 1950s to increase fishery yields. Commercial catches did indeed rise—but at the same time, the Nile perch played a major role in the collapse of the lake’s extraordinarily diverse native fish community. Its endemic cichlids were particularly severely affected.

It is no longer possible to determine exactly how many fish species actually became extinct as a result of this ecological upheaval. The lake’s biodiversity had never been fully documented beforehand. Around 200 cichlid species disappeared from scientific catches, at least temporarily, or suffered severe declines; higher estimates suggest that up to 400 fish species disappeared. Some species that had not been recorded for a long time, including Haplochromis microdon and H. vonlinnei, were later rediscovered in small remnant populations.

However, the decline of the fish community cannot be attributed solely to these two invasive species. In addition to Nile perch and water hyacinth, overfishing, high nutrient inputs, oxygen depletion, and other habitat changes contributed to Lake Victoria’s ecological crisis.

Nile perch and water hyacinth reached Africa for different reasons, but both cases have the same origin: human actions. Nile perch was deliberately released to boost fisheries, while water hyacinth was introduced as an ornamental plant and later entered natural bodies of water. Biological invasions are therefore not the introduced species’ “fault”. They begin when people intentionally or unintentionally transport organisms beyond their natural ranges.

How invasive species contribute to extinction

Not every alien species becomes invasive. Alien species are considered invasive when they establish and spread in a new area and demonstrably harm nature or people.

Their ecological consequences range from competition for food and habitat to predation and the transmission of diseases, as well as the alteration of entire habitats. The 2023 report by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) shows the role invasive species play in global extinction: They contributed to 60% of documented global extinction events involving animal and plant species. In 16% of these extinction events, they were even the only identified driver.

This does not mean that invasive species alone caused 60% of all extinction events. They often act in combination with other pressures such as habitat loss, overexploitation, pollution, or climate change.

Prevention is more effective than controlling invasions later

Once an invasive species has spread over a large area, controlling it often requires considerable effort. Complete eradication is then frequently no longer feasible. The researchers therefore emphasize that prevention is the most effective and usually also the most cost-effective approach.

This includes inspections along major trade and transport routes, mandatory biosecurity standards, early monitoring of potential points of entry, and adequately resourced authorities. If a newly introduced species is detected in time, it may still be possible to contain its spread or eradicate the population entirely.

Biological invasions are not a purely local environmental problem. Animals, plants, fungi, and pathogens reach new regions through international flows of goods, travel, and transport routes. Successful prevention therefore requires cross-border cooperation as well as support for countries where biodiversity is particularly high but resources for monitoring and management are limited.

The distribution of research funding also plays an important role. If research continues to focus primarily on Europe, North America, and other affluent regions, there is a risk that conservation measures and funding will not reach the places where invasive species cause particularly severe and potentially irreversible damage.

Implications for research and conservation

The study corrects a distorted picture of the global consequences of invasive species. Although more alien species and far more cases of damage are documented in the Global North, the ecological impacts are more severe on average in the Global South.

Rapidly growing economies are particularly at risk: Trade and the movement of goods are increasing rapidly, while monitoring, prevention, and management are not being expanded at the same pace. In these countries, a growing risk of introductions coincides with high biodiversity and limited government capacity.

The findings call for more than just additional research in the Global South. Above all, stronger international biosecurity, capable authorities, early detection of new invasions, and more equitable funding for prevention and management are needed. In the future, conservation measures should be guided less by where the most data are available and more by where invasive species cause the most severe and potentially irreversible damage.

Overall, the study’s findings are alarming: Many of the most biodiverse regions on Earth are the most at risk, yet they often have the fewest resources to monitor and contain invasive species. Without stronger international support, extinction could accelerate further in these regions.

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Sources

• Bacher, S., Pyšek, P., & Seebens, H. (2026). Invasive species’ environmental impacts are more severe in the Global South. Science, 393(6809), 376–380. https://doi.org/10.1126/science.aed0603
• Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. (2023). Thematic assessment report on invasive alien species and their control (H. E. Roy, A. Pauchard, P. Stoett, & T. Renard Truong, Eds.). IPBES Secretariat. https://doi.org/10.5281/zenodo.7430682
• Justus Liebig University Giessen. (2026, July 24). Invasive species hit the Global South significantly harder than previously assumed. JLU. https://www.uni-giessen.de/de/ueber-uns/pressestelle/pm/pm109-26invasiveartenglobalersueden
• Michelitsch, M. (2026, July 27). Invasive Arten schaden Globalem Süden stark. ORF Science. https://science.orf.at/stories/3236654/