1. Plant tolerance to herbivory has been accepted as a mechanism of defense that can be expressed jointly with resistance. Recent advances have partially validated previous theoretical predictions and improved our understanding of tolerance. Here, I highlight the necessity of integrating tolerance into ecological and co-evolutionary theory to better understand the biology of this defensive mechanism.
2. Existing work has been biased toward understanding the adaptive nature and constraints acting on tolerance rather than its ecological implications. Increasing consensus that tolerance may alter the classical antagonistic dynamic between plants and herbivores suggests possible avenues to explore its population and community consequences.
3. In this review, I summarize previous advances in the ecology and evolution of tolerance to herbivory. I also discuss recent evidence that improves our understanding of unresolved issues such as the specificity of tolerance in response to herbivory, its role as an agent of selection on herbivores, and its ecological and evolutionary consequences which include a role of tolerance during biological invasions.
4. Although there is good support for an adaptive role of tolerance in response to herbivory damage, tolerance can itself impose selection on herbivores. Furthermore, tolerance can influence herbivore population dynamics and coexistence, as recent studies show that tolerance responses increase diversity of the associated herbivore communities on individual host plants.
5. Future studies that take into account the role of herbivores on the expression of tolerance will provide novel insight that will help disentangle the mechanisms of tolerance and its ecological and evolutionary implications.