Overcompensatory plant responses to insect herbivory: A meta-analysis

Overcompensation is a plant response to herbivory in which damage increases the photosynthetic rate, growth, or reproductive output of an injured plant compared to an undamaged plant.   We conducted a meta-analysis to assess the extent of this phenomenon in nature and to determine the prevailing mechanisms and conditions that facilitate this plant response to insect herbivores. Specifically, we ask (1) what is the extent of overcompensation among plant and herbivore taxa? (2) under what biotic and abiotic experimental conditions are overcompensatory responses most likely to occur? and (3) what mechanisms prevail as the physiological basis for plant overcompensation for insect herbivory? We found 64 studies reporting overcompensatory plant responses to insect herbivory that met the criteria for inclusion in our analysis, allowing us to conclude that overcompensation may be more widespread that previously recognized. For instance, evidence for overcompensation was found among 53 natural and 11 agricultural systems comprising 26 plant families and 22 insect herbivore families.  The magnitude of overcompensatory effects, however, varied greatly among plant and insect taxa.  Phloem feeding or cell content feeding insects, for example, induced significantly larger overcompensatory effects than chewing insects.  Furthermore, perennial plants and tropical plants overcompensated more than annual and temperate plants, respectively. This indicates that plant life history and ecosystem habitat are important influences on plant overcompensatory responses. In contrast to our expectations, however, overcompensatory responses were of similar magnitude in agricultural systems and in natural systems and the amount of damage caused by herbivores did not result in variation in the magnitude of overcompensation by plants.  Finally, plants overcompensated via a variety of mechanisms, including reallocating resources, releasing apical dominance, and increasing photosynthetic rates.  Our results suggest that overcompensation for insect herbivory is a widespread conditional plant response and further study is needed to clarify the ecological and evolutionary significance of overcompensation and the potential for plant herbivore mutualisms to exist.