HERBIVORY AFFECTS DEVELOPMENTAL INSTABILITY OF STONE OAK, QUERCUS-ROTUNDIFOLIA

The effects of herbivory on plant fitness have traditionally been asse ssed by reductions in performance measured in terms of physiological, growth, and reproductive parameters. We investigated the direct effect of herbivory on a measure of foliar developmental instability (fluctu ating asymmetry in leaf width) in evergreen stone oak. Quercus rotundi folia. Since leaves from more than a single growth season are present simultaneously, it is possible to compare measures of developmental in stability of newly formed leaves in relation to the extent of herbivor y in the previous season as assessed from damage to old leaves. We fou nd significantly increased asymmetry in leaf width when leaves From th e previous year showed signs of herbivory. This result was confirmed e xperimentally by using leaf removal to mimic herbivory. Oak trees wher e many old leaves were removed had increased foliar asymmetry compared to oak trees where only few leaves had been removed and untreated con trol trees. Using foliar asymmetry in old leaves from the previous yea r as a baseline for these comparisons confirmed that foliar asymmetry of individual trees increased as a consequence of herbivory. Oak trees with high degrees of asymmetry were more likely to die than oak trees with low asymmetry. These results suggest that foliar asymmetry is sy mptomatic of a stressed plant. Herbivores can both produce such a stre ss, leading to increased asymmetry, and attack differentially more asy mmetric plants. In the extreme, the most asymmetric plants are those m ost likely to die.