Study finds some species arrive pre-adapted to outcompete natives - even in intact ecosystems.
Plants that become invasive may owe their success to an advantage shaped long before they arrive, according to new research led by King's College London.
Think of Japanese knotweed in the UK or kudzu in the United States - plants that seem almost unstoppable once established. New research suggests their success may not just be about where they arrive, but the evolutionary environments they come from.
The study provides experimental evidence for the "evolutionary imbalance hypothesis" - a theory suggesting that species from highly competitive and evolutionarily diverse environments are better equipped to dominate when introduced elsewhere.
To test this, researchers conducted grassland experiments across Central Europe, introducing 166 plant species into existing communities and tracking their survival over multiple growing seasons. The findings show that plants originating from regions with high phylogenetic diversity - meaning they evolved among a wide range of distantly related species - were significantly more likely to establish and survive in their first year.
Crucially, these species performed just as well in undisturbed environments as in disturbed ones. Disturbance, such as soil disruption or land use change, is typically considered essential for enabling invasions by reducing competition. However, in this study, some species appeared able to overcome competition without that advantage.
By contrast, plants from less diverse evolutionary backgrounds relied heavily on disturbance to establish. Without it, they struggled to survive, highlighting how evolutionary history shapes competitive ability.
The researchers also identified the importance of relative phylogenetic diversity - comparing the evolutionary diversity of an incoming species' native range with that of the community it enters. Species were most successful when they came from more diverse regions than the ecosystems they invaded. In undisturbed plots, survival into the second year only occurred when this imbalance favoured the newcomer.
Climate compatibility still played a key role. Plants were more likely to succeed when their native climates resembled the new environment, particularly in rainfall patterns. However, species from highly diverse regions sometimes coped better with temperature differences, suggesting evolutionary advantages can partially offset environmental mismatches.
Analysis of plant traits revealed that species from high-diversity regions tended to produce heavier seeds and exhibit characteristics linked to rapid growth and efficient resource use. These traits likely support successful establishment in competitive settings. Yet evolutionary background remained a strong predictor of success even after accounting for these factors, indicating a broader advantage beyond measurable traits.
The findings have important implications for predicting and managing invasive species. Regions with high evolutionary diversity may act as sources of particularly competitive invaders, while ecosystems with lower diversity - including islands - may be more vulnerable.
Although the advantage was strongest in early stages, gaining a foothold is often decisive in invasion success. The study suggests that for some plants, that success is shaped long before they spread.
