1. Many plants compensate for the damage caused by herbivorous insects
through tolerance responses. Besides directly causing plant tissue loss
and seed production reduction, herbivory causes phenological changes in
the host plant. However, little is known about the fitness costs of
phenological changes caused by tolerance responses to herbivorous
attacks. 2. The girdling beetle Phytoecia rufiventris caused a
short-term decrease in the number of flowers of the host plant
Erigeron annuus. However, accelerated growth restored the number
of flowers, but after a 2-week delay. With an objective to examine
whether the tolerance response with such a delay fully compensates the
fitness, we experimentally reproduced a 2-week delay in germination
under greenhouse and field settings. Under both conditions,
intraspecific competition resulted in serious defects in the growth and
reproduction of E. annuus plants which of germination was
delayed. However, delayed germination resulted in better growth when
competition and herbivory were eliminated from the field. 3. Thus, we
showed that the tolerance response to restore reproductive production
does not fully compensate for the fitness loss caused by insect attack;
rather, the delay in seed production in attacked plants leads to delayed
germination and subsequent inferiority in intraspecific competition. 4.
Synthesis. Our results imply that compensation for floral production
after an herbivore attack does not fully restore offspring fitness in
the presence of intraspecific competition and herbivory. Assessing the
ecological consequences of defense traits in an appropriate layer of
interaction is critical to interpreting adaptive values.