<b>Assessing the evidence for the performance-defense trade-off in the EICA hypothesis </b>

One long-standing idea is that plants that escape their natural enemies abroad can redirect resources from chemical defense into growth and reproduction, giving them greater competitive ability. The idea is known as the “Evolution of Increased Competitive Ability (EICA)”, and a recent study has found that a widespread weed evolves greater competitive ability wherever it invades, pointing to this hypothesis as a possible cause.

However, the studies cited report contrasting responses to herbivores and soil biota, without directly testing resource reallocation between defense and growth. In this contribution we add an independent comparison among populations showing opposite geographic trends in defense and performance indices in <i>Taraxacum officinale</i>. These patterns highlight the need to test resource reallocation rather than establish that it occurs.</p>