Plant invaders may gain an edge from evolutionary history

Plants that become invasive may have an advantage before they reach a new ecosystem, according to research led by King's College London. The findings suggest that some plants succeed because they evolved in regions where competition among distantly related species was especially strong.

The study tested the evolutionary imbalance hypothesis, which holds that species from highly competitive and evolutionarily varied environments can be better prepared to dominate when introduced elsewhere. That idea could help explain why plants such as Japanese knotweed in the U.K. or kudzu in the United States can become difficult to control once established, according to King's College London.

Researchers ran grassland experiments across central Europe, introducing 166 plant species into existing plant communities and following their survival over several growing seasons. They found that plants from regions with high phylogenetic diversity, meaning places where species evolved alongside many distantly related plants, were more likely to establish and survive during their first year.

The result points to a role for evolutionary history in invasions, beyond the conditions a plant encounters after arrival. According to the researchers, plants from more diverse evolutionary backgrounds appeared better able to compete in their new communities.

One striking finding involved disturbance. Ecologists often view soil disruption, land-use change and similar disturbances as openings that help nonnative plants gain a foothold by weakening existing competition.

In the experiments, however, plants from highly diverse evolutionary regions performed as well in undisturbed plots as they did in disturbed ones, according to King's College London. Plants from less diverse evolutionary backgrounds depended more heavily on disturbance; without it, they were less likely to persist.

The researchers also examined relative phylogenetic diversity, comparing the evolutionary diversity of a plant's home region with that of the community it entered. Species had the greatest success when they came from regions more evolutionarily diverse than the ecosystems they were introduced into.

That imbalance was especially clear in undisturbed plots. According to the study, plants survived into a second year in those settings only when the evolutionary comparison favored the newcomer.

Climate still mattered. Plants were more likely to establish when their native climate resembled the new environment, especially in rainfall patterns, the researchers reported.

But the study also found that species from highly diverse regions sometimes handled temperature differences better than other plants. King's College London said that suggests evolutionary advantages may partly offset some environmental mismatch, though not replace the importance of climate fit.

The team also looked at plant traits linked to establishment. Species from high-diversity regions tended to have heavier seeds and traits associated with fast growth and efficient use of resources, according to the study.

Those characteristics may help plants compete early in a new community. Even after accounting for those traits, however, evolutionary background remained a strong predictor of success, the researchers found.

The findings could affect how scientists and land managers assess invasion risk. King's College London said regions with high evolutionary diversity may be sources of especially competitive plant invaders, while ecosystems with lower diversity, including islands, may face higher vulnerability.

The advantage identified in the experiments was strongest during the early stages of establishment. For invasive plants, that early foothold can be decisive, and the study suggests that part of that success may be shaped long before a plant spreads into a new range.

This story draws on original reporting from Phys.org.