Invasive alien species represent one of the most destructive yet overlooked pressures on biodiversity. The 2019 IPBES Global Assessment Report identified invasive alien species as one of five main direct drivers of biodiversity loss worldwide. Despite this significance, the threat posed by invasive species to biodiversity, ecosystem services, and human well-being remains generally little understood and poorly quantified by decision makers.
What are invasive species?
Alien species are organisms found outside their natural range due to human activities. When these species proliferate — often due to absent natural predators — and cause significant negative impacts, they become classified as "invasive alien species" (IAS). IAS reduce species diversity by outcompeting native species, potentially disrupting ecosystem services.
This process, called "biological invasion," involves human activities intentionally or unintentionally transporting and introducing species to new regions outside their natural range, where they establish, spread, and cause ecological disruption.
What is the current situation with IAS?
The global spread of IAS accelerates at an unprecedented pace. Over 37,000 established alien species have been introduced by humans across all regions and biomes. New alien species are recorded at approximately 200 per year, with around 3,500 classified as invasive alien species (IPBES, 2023).
IAS are present on every continent, with approximately 20% of global land area classified as highly vulnerable to invasion (Early, R. et al., 2016). They have contributed — solely or combined with other drivers — to approximately 60% of recorded global extinctions, with 90% occurring on islands where ecosystems are more fragile. They are the sole driver in 16% of documented global plant and animal extinctions.
Economic Impact: The economic cost of biological invasions has quadrupled every decade since 1970, reflecting direct damages (agricultural productivity loss, infrastructure damage) and indirect costs (biodiversity loss, ecosystem service degradation). In 2019, the estimated global annual economic cost reached a staggering $423 billion (IPBES, 2023).
Additionally, 8% of IAS cases negatively impact human health by spreading diseases, causing allergies, or disrupting ecosystem-dependent livelihoods.
What are famous examples of IAS?
European rabbits in Australia: Originally introduced in 1859 for hunting, just 24 rabbits rapidly multiplied due to absent natural predators. By the 1880s, they had spread across millions of hectares, causing widespread overgrazing, soil erosion, and native species decline. Rabbits remain a major ecological and economic threat today.
Amazon water hyacinths: First introduced to North America in 1884 as ornamental plants, water hyacinths spread rapidly due to fast reproduction rates, doubling their mass in two weeks under optimal conditions. By the mid-20th century, they became a global invasive species, choking waterways, reducing water quality, and disrupting fisheries in regions like Africa's Lake Victoria and Southeast Asia.
European shore crab in North America: Believed to have arrived in the early 1800s via ballast water from European ships, the shore crab established along the Atlantic coast by the 1900s. Its spread accelerated in the late 20th century along the Pacific coast, decimating shellfish beds, causing multi-million-dollar fisheries losses, and disrupting marine ecosystems by preying on native shellfish and competing with local species.
Why are impacts of IAS hard to quantify & modelise?
Despite significant impacts, IAS remain challenging to model:
- Context-dependent impacts: Effects of IAS vary greatly depending on region, species interactions, and local environmental conditions.
- Lag effects complicating baselines: Some invasions take decades to manifest ecological consequences, making baseline measurements difficult.
- Limited global datasets: Unlike GHG emissions or land use change, consistent, comparable global data on IAS introductions and spread is lacking.
- Complex feedback loops: Direct and indirect ecosystem changes create difficult-to-predict future threats.
Critical gaps persist: quantifying links between economic activities and IAS introduction drivers, and connecting introduction drivers to biodiversity impacts. Consequently, ecological impacts aren't integrated into Life Cycle Impact Assessment (LCA) frameworks. LCAs evaluating trade-related impacts underestimate the full environmental consequences of commodity transportation, potentially yielding incomplete risk assessments.
Emerging Research: Promising research is emerging to address these gaps. The work by J. Borgelt et al, published in 2024, developed country-to-country Characterization Factors (CFs) assessing biodiversity impacts linked to unintentional alien species spread through global goods transportation. The team designed globally applicable CFs quantifying damage from introduced alien species to terrestrial ecosystems based on origin-destination trade routes. CFs utilize the Potentially Disappeared Fraction (PDF) of terrestrial species as the primary metric, quantifying ecosystem damage per kilogram of transported goods in the importing country.
How do we take IAS into account at darwin?
Darwin leverages international transport of goods as a proxy to assess biological invasion risk. Since human activities — particularly global trade, transportation, and habitat modification — are main species introduction drivers, businesses' exposure to global trade intensity serves as a proxy for assessing IAS risk. The assumption is: higher trade flow (imports/exports, shipping routes, tourism) correlates with greater invasion risk, and high-risk industries (agriculture, forestry, aquaculture, pet trade) have stronger links to species introductions.
While not perfect, trade exposure provides a scalable and quantifiable way to assess the risk of biological invasions in biodiversity footprint assessments. Darwin continues refining its pressures framework and welcomes relevant IAS modeling and impact assessment research.
Global trade is a key driver of biodiversity risk. Don't let invasive species threaten your value chain. Integrate this key pressure into your biodiversity assessment with darwin.