Overcompensatory plant responses to insect herbivory: A meta-analysis of the prevalence and conditions

Background/Question/Methods

Plants respond to insect herbivory in myriad ways.  Following injury, they may be unable to recover, perform just as well as if they were undamaged, or have increased growth and/or fitness. These responses have been termed under-compensation, compensation, and overcompensation, respectively. Overcompensation is a particularly controversial phenomenon in which herbivory increases the photosynthetic rate, growth, or reproductive output by the injured plant.  No reviews currently assess the prevalence of this phenomenon resulting from insect herbivory.  Here we conduct a meta-analysis to characterize overcompensation. We ask (1) what is the prevalence of overcompensation across plant and herbivore taxa, and (2) under what biotic and abiotic experimental conditions are overcompensatory responses most likely to occur?

Results/Conclusions

Over 50 studies reported significant overcompensatory responses to insect herbivory and met the criteria for inclusion. Overall, the overcompensatory responses reported were of large effect. However, overcompensatory responses were of higher effect in agricultural systems than in natural systems. In agricultural systems, overcompensatory reproduction and photosynthesis were of higher magnitude than overcompensation in vegetative growth.  There are no such distinctions in natural systems and there are no differences in the positive effects of herbivore damage in studies that used simulated or actual insect herbivory.  Regardless, overcompensatory responses were strongest when plants experienced low levels of damage.  Studies that utilized growth chambers found smaller overcompensatory effects than field, greenhouse or garden studies.  Also, tropical systems experience higher overcompensatory effects than temperate systems.   Annual and perennial plants overcompensated to similar a degree, but annuals responded to herbivores with greater reproductive and photosynthetic overcompensation, than vegetative overcompensation.  Finally, overcompensatory effects differed following damage across various insect feeding guilds.  Phloem feeding and cell content feeding insects induced higher overcompensatory effects in their host plants than chewing insects. Overall, this study suggests that overcompensatory responses may be underreported due to experimental design bias to measure herbivore impacts following severe levels of plant injury. This analysis also indicates that overcompensation for insect herbivory is a conditional plant response much like other conventional plant-insect mutualisms.