Understanding Biological Invasion: Threats to Biodiversity and Ecosystems

Every year, thousands of species travel across borders – not through natural migration, but through human activity. These non-native organisms, when they establish themselves in new environments and begin to outcompete local life, become what scientists call invasive alien species (IAS). They are now recognised as one of the top five drivers of biodiversity loss on the planet, alongside habitat destruction, overexploitation, climate change, and pollution. Understanding how biological invasions work – and the damage they cause – is essential for anyone concerned about the future of our ecosystems.

What are invasive alien species? 🔗

Invasive alien species are plants, animals, or other organisms that are introduced – intentionally or accidentally – into regions outside their natural range, where they go on to cause harm. According to the International Union for Conservation of Nature (IUCN), IAS negatively impact native biodiversity, ecosystem services, and in many cases, human well-being. Not every introduced species becomes invasive; the label applies specifically to those that establish self-sustaining populations and cause measurable ecological or economic damage.

A landmark 2023 assessment by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) found that over 37,000 alien species have been introduced globally through human activities, and more than 3,500 of these are classified as harmful invasive species. The rate of introductions is accelerating, with roughly 200 new alien species documented each year. These invasions have been a contributing factor in approximately 60% of all known global species extinctions.

How do invasive species establish and spread? 🔗

Invasive species share a set of biological traits that give them a competitive edge in new environments. These include rapid growth rates, high reproductive output, broad habitat adaptability, and efficient dispersal mechanisms. Many invasive plants, for instance, produce thousands of seeds that remain viable for years, allowing them to spread aggressively even after initial removal efforts.

The role of allelopathy 🔗

One particularly effective invasion mechanism is allelopathy – the production of biochemical compounds that suppress the growth of neighbouring plants. Several invasive species release water-soluble chemicals through their roots, leaves, or decomposing litter that inhibit seed germination and seedling growth of native species. Prosopis juliflora, for example, produces phenolic compounds in its leaf litter that significantly reduce the survival and growth of native Indian plant species. Research published in PLOS ONE showed that the canopy effects of P. juliflora were strongly negative on species richness in India and Hawaii, while the same tree had facilitative effects in its native range of Venezuela.

Dispersal and human-assisted pathways 🔗

Global trade, shipping, and travel have become the primary pathways for invasive species to reach new territories. A 2017 study found that over one-third of all species introductions in the past two centuries occurred after 1970, coinciding with the acceleration of global commerce. Seeds travel in cargo, aquatic organisms hitchhike in ballast water, and insects stow away in wood packaging. In many cases, species were deliberately introduced for economic or environmental purposes – and then got out of control.

Ecological impacts of biological invasions 🔗

The ecological consequences of invasive species are far-reaching and often irreversible. IAS are the second most common cause of species extinctions globally, according to the IUCN Red List. Islands are particularly vulnerable – around 90% of extinctions linked to invasive species have occurred on islands, where endemic species have evolved in isolation and lack defences against new predators or competitors.

Terrestrial ecosystems 🔗

On land, invasive plants alter soil structure, change nutrient cycling, and shift decomposition processes. Chromolaena odorata, an aggressive shrub native to the Americas, has now spread across tropical Asia and Africa. It suppresses native vegetation through allelopathic effects and sheer competitive dominance. In India, it is one of the fastest-expanding invasive plants. A 2025 study reported by Down To Earth found that C. odorata was spreading at nearly 1,988 sq km per year and had nearly doubled its range in the Western Ghats and the northeast within two decades. Overall, India’s natural areas are losing an estimated 15,500 sq km annually to invasive plant species.

Invasive insects also cause massive damage. The Asian long-horned beetle (Anoplophora glabripennis), native to East Asia, attacks hardwood trees and has caused significant losses in forests across North America and Europe. If left unchecked, such pests can devastate millions of acres of timber.

Aquatic ecosystems 🔗

Water hyacinth (Eichhornia crassipes) is one of the most notorious aquatic invaders in the world. Native to South America, this free-floating plant reproduces rapidly through both seeds and runners, forming dense interlocking mats on the surface of lakes, rivers, and wetlands. These mats block sunlight penetration, reduce dissolved oxygen levels, and alter water chemistry, leading to significant declines in native fish and aquatic plant populations. In Ethiopia’s Lake Tana, the weed appeared in 2011 and covered over 500 sq km of the water surface by 2014, severely disrupting fisheries, irrigation, and transport.

Economic and social costs 🔗

Biological invasions carry an enormous economic price tag. The IPBES assessment estimated that the global economic cost of invasive species exceeds $423 billion annually, with costs quadrupling every decade since the 1970s. In Europe alone, the total cost of biological invasions between 1960 and 2020 was estimated at nearly $130 billion.

Agriculture is one of the hardest-hit sectors. Invasive weeds reduce crop yields, increase the cost of pest management, and degrade pastureland. For rural and pastoral communities, the impacts are immediate – invasive plants reduce fodder and fuelwood availability, deplete soil fertility, and can even trigger respiratory illnesses. Each hectare lost to invasion translates directly into lost income and food security for vulnerable households.

Invasive species also pose risks to human health. The Asian tiger mosquito (Aedes albopictus), which has spread globally via shipping, is a vector for diseases like dengue fever and chikungunya. It contributed to a major outbreak in the Indian Ocean islands in 2005-2006 that infected more than 272,000 people.

Case studies: three invasive species in detail 🔗

Eichhornia crassipes (water hyacinth) 🔗

Originally from the Amazon basin, water hyacinth is now found in over 50 tropical and subtropical countries. It is one of the most invasive aquatic plants worldwide, capable of producing 60-100 tonnes of biomass per hectare per year. Its thick floating mats create stagnant, low-oxygen conditions underneath that suffocate aquatic life. It clogs waterways, disrupts hydroelectric generation, and hampers fishing communities. Management efforts – mechanical removal, chemical treatment, and biological control – continue, but no single strategy has proven fully effective.

Prosopis juliflora (mesquite) 🔗

This thorny tree, native to Central and South America, was introduced to India in the 19th century to combat desertification and provide firewood. Today, it dominates vast stretches of arid and semi-arid land. In Gujarat’s Banni grasslands – India’s largest – the tree has taken over roughly 50% of the grasslands since its introduction in 1961, displacing native grasses that sustain livestock herding communities. It replaces native species like Acacia nilotica, Prosopis cineraria, and Salvadora persica, and its leaf litter suppresses the germination of other plants.

Yet P. juliflora presents a management dilemma. Despite its invasive nature, it provides tangible benefits to local communities: charcoal production, firewood, soil conservation, and even animal feed from its pods. For marginalised groups like the Jogi tribe in Rajasthan, charcoal-making from this tree has become an essential livelihood. Experts recommend controlling its spread rather than attempting complete eradication, and finding ways to use the species productively while restoring native habitats.

Chromolaena odorata (Siam weed) 🔗

Chromolaena odorata is an aggressive perennial shrub that forms dense thickets, smothering native vegetation in tropical forests and grasslands. It thrives in disturbed habitats, regenerates quickly after cutting, and produces allelopathic substances that prevent other plants from establishing. Across India, it is one of at least 11 major invasive plant species now present in nearly two-thirds of the country’s natural ecosystems. Its rapid expansion poses a direct threat to biodiversity in protected areas, wildlife habitats, and agricultural margins.

Climate change and invasive species: a compounding crisis 🔗

Climate change and biological invasions reinforce each other. Warmer temperatures and changing rainfall patterns open up new territories for invasive species while weakening native ecosystems’ resilience to invasion. The IUCN notes that climate change facilitates the establishment and spread of many alien species, creating new opportunities for them to become invasive. At the same time, invasive species reduce the ability of natural habitats and agricultural systems to cope with climate impacts – creating a feedback loop that accelerates biodiversity loss.

For instance, flooding events can carry invasive seeds and propagules into new areas. Rising temperatures allow tropical invasive species to expand into previously cooler regions. And well-intentioned climate mitigation projects, such as large-scale tree planting, can actually worsen the problem if non-native species like Acacia or Eucalyptus are used instead of indigenous alternatives.

Global policy responses 🔗

Addressing invasive species requires coordinated international action. The Kunming-Montreal Global Biodiversity Framework, adopted in 2022 under the Convention on Biological Diversity (CBD), includes Target 6, which specifically calls for reducing the rate of introduction and establishment of invasive alien species by at least 50% by 2030, and for managing or eradicating IAS to reduce their impacts on biodiversity and ecosystem services.

In 2025, the CBD published an Invasive Alien Species Toolkit to support countries in developing national strategies and action plans aligned with Target 6. The European Union also has specific regulations – including Regulation (EU) No 1143/2014 – that restrict the import, trade, and release of listed invasive species. The EU Biodiversity Strategy for 2030 aims to halve the number of Red List species threatened by IAS.

Prevention remains the most cost-effective approach. Biosecurity measures to intercept IAS at borders, early detection and rapid response systems, and public awareness campaigns are all critical. Once an invasive species is established, control and management become far more expensive and less certain.

The way forward 🔗

Managing biological invasions is not a simple eradication problem. As the Prosopis juliflora case shows, some invasive species become deeply embedded in local economies and ecosystems. Effective strategies require balancing ecological restoration with socio-economic realities, engaging local communities, and integrating IAS management into broader climate, agriculture, and development policies.

What is clear is that inaction is not an option. With introduction rates at historic highs and climate change expanding the playing field for invasive organisms, the window for effective intervention is narrowing. Investments in research, monitoring, and cross-border cooperation are essential to protect native biodiversity and the livelihoods that depend on healthy ecosystems.

What do you think? Should the management of invasive species like Prosopis juliflora prioritise complete eradication or controlled coexistence that accounts for the livelihoods of local communities? And in your region, are there invasive species that people have come to depend on despite their ecological costs?

References

1. https://iucn.org/our-work/topic/invasive-alien-species
2. https://www.ipbes.net/IASmediarelease
3. https://pmc.ncbi.nlm.nih.gov/articles/PMC3440363/
4. https://iucn.org/resources/issues-brief/invasive-alien-species-and-sustainable-development
5. https://www.downtoearth.org.in/wildlife-biodiversity/indias-natural-areas-losing-15500-sq-km-a-year-to-fast-spreading-invasive-species
6. https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2427.2009.02294.x
7. https://onlinelibrary.wiley.com/doi/10.1155/2023/4618069
8. https://www.sciencedirect.com/science/article/pii/S2772735125000022
9. https://india.mongabay.com/2021/08/large-scale-removal-of-bannis-invasive-mad-tree-prosopis-is-not-the-solution-study/
10. https://www.frontiersin.org/journals/conservation-science/articles/10.3389/fcosc.2024.1491618/full
11. https://iucn.org/resources/issues-brief/invasive-alien-species-and-climate-change