When invasive plants break the rules

Why do some invasive plants become so successful, while many introduced species remain uncommon or fail to establish at all?

Invasion ecology has often approached this question by looking for traits that give introduced plants an advantage over native species. Successful invaders may grow quickly, produce many seeds, disperse over long distances, capture resources efficiently, or tolerate disturbance. But plants have finite resources, so advantages in one function are generally expected to come with costs in another. A species that invests heavily in rapid growth, for example, may have less capacity to tolerate drought or nutrient limitation. A species that produces many small, easily dispersed seeds may be less competitive after establishment. These trade-offs help organize plant strategies and contribute to the coexistence of species within native communities.

Our new paper in Trends in Ecology & Evolution asks what happens when invasive plants do not follow these expected rules.

Many invasive species probably succeed by shifting toward one end of a familiar trade-off. A fast-growing invader may outperform native plants under favorable conditions, but remain relatively vulnerable to drought, shade, herbivory, or other stresses. The underlying trade-off still applies. The invader has simply adopted a more extreme strategy. In other cases, however, invaders appear to move beyond the range of trait combinations expressed by native species. They may grow rapidly while using water efficiently, disperse widely while remaining strong competitors, or combine high growth with strong chemical defense. We call this pattern trade-off escape: the relaxation or reversal of constraints among ecologically important functions that normally limit the strategies available to plants.

The paper focuses on three major trade-offs that frequently structure plant communities:

The first is the competition–colonization trade-off. Plants that disperse effectively often produce many small seeds, while strong competitors tend to be larger and invest more heavily in each offspring. Across the California flora, native species show a relationship between seed size and plant height consistent with this trade-off. Some nonnative species do not. Black mustard, for example, combines small, readily dispersed seeds with tall stature and high reproductive output.

The second is the growth–stress tolerance trade-off. Rapid growth often depends on resource-acquisitive tissues that perform well when conditions are favorable but are less resistant to drought, flooding, low nutrients, or shade. Yet invasive annuals in desert and Mediterranean systems have been shown to combine high relative growth rates with high water-use efficiency. Other invaders combine strong competitive ability with flooding tolerance or maintain both rapid growth and survival under low light.

The third is the growth–defense trade-off. Classic invasion hypotheses often predict that plants released from specialist herbivores or pathogens will reduce investment in defense and redirect those resources toward growth and reproduction. Some invaders fit that pattern. Others appear able to grow faster while maintaining or even strengthening defense. Several invasive species have outperformed native relatives in both growth and chemical defense, suggesting that the expected cost of maintaining both functions has weakened.

These examples span grasslands, deserts, forests, wetlands, and multiple continents. Trade-off escape is not universal, but it may help explain why a relatively small number of introduced species become especially dominant or ecologically disruptive.

You can read the full paper here.

Valliere, J. M., & Funk, J. L. (2026). Trade-off escape as a framework for understanding plant invasions. Trends in Ecology & Evolution.