Modelling compensatory regrowth with bud dormancy and gradual activation of buds |
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Authors: | Kari Lehtilä |
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Institution: | (1) Department of Botany, University of Stockholm, Stockholm, Sweden |
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Abstract: | Many plants show compensatory regrowth after herbivory and dormant buds often have an important role in compensatory responses.
Theoretical models have shown that herbivore damage may select for a bud bank, i.e., a pool of dormant buds that are protected
from herbivory and that are activated after herbivore damage. Earlier models assumed that undamaged plants cannot activate
their dormant buds without damage, although they apparently have sufficient resources for successful seed production through
the additional shoots dormant buds could produce. However, many plants are able to gradually activate buds over an extended
period of time without any cue from damage. The aim of this study was to analyze how herbivory imposes selection for gradual
mobilization of the bud bank. I assume that selection pressures that affect the fraction of buds active at each time point
include damage by herbivores, time left to the end of season, and the opportunity costs of dormant buds. I modelled bud dynamics
with gradual activation when there is a single damage event and (i) when the seed set of a shoot is not dependent on the time
it is active, or (ii) when the seed set of a shoot diminishes with later activation. In addition, I analyzed how (iii) risk
of repeated herbivory affects selection for gradual activation. Under these models, gradual activation is optimal over a wide
range of herbivory pressures. Selection appears to favour activation of all buds at the beginning of the season only when
herbivore pressure is weak and when early shoots have a higher seed set than late shoots. Alternatively, strong herbivore
pressure and late damage may select for a large bud bank throughout the growing season, without gradual activation; the bud
bank is only mobilized after damage. In this case, damaged plants can overcompensate, i.e. they have a higher seed set than
undamaged plants with the same bud activation pattern. Selection for overcompensation demands a stronger herbivore pressure
in this current model than in earlier bud bank models. The model never predicts selection for overcompensation when there
is a risk of repeated herbivory.
This revised version was published online in July 2006 with corrections to the Cover Date. |
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Keywords: | bud bank bud dormancy compensatory response herbivore tolerance phenology |
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