DOI: 10.5061/dryad.x3ffbg7dz
title: Data from: Induced phenological avoidance: a neglected defense mechanism against seed predation in plants

description: 1.    Flowering phenology is an important life history
 trait affecting plant reproductive performance and is influenced by
 various abiotic and biotic factors. Pre-dispersal seed predation and
 pollination are expected to impose counteracting selection pressure on
 flowering phenology, with pre-dispersal seed predation expected to favor
 off-peak flowering and pollination to favor synchronous
 flowering.  2.      Here we studied
 the effect of pre-dispersal seed predation by the beetle Byturus
 ochraceus, a specialist seed herbivore, on the flowering phenology of Geum
 urbanum. This forest understorey plant species is self-pollinating, so
 that the influence of seed predation can be studied independent from
 pollination. We measured in detail the timing and predation rate of
 individual flowers during two consecutive years in more than 60
 individuals. We tested the hypotheses that pre-dispersal seed predation
 exerts selection for within-season compensatory flowering as well as for
 induced phenological avoidance in the following season. 3. 
     We found no indication for compensatory flowering
 within a growing season, but plants that experienced predation shifted
 their flowers to the end of the flowering season the subsequent year. This
 induced phenological avoidance points to a plastic response to
 pre-dispersal seed predation that may be adaptive. Importantly, the delay
 in flower production came at a cost, since flowers later in the season had
 a reduced seed output, presumably because of increasing light limitation
 following forest canopy closure.  4.   
   Synthesis: Herbivory by specialist enemies can cause serious
 fitness decline in hosts. We here show that induced shifts in phenology
 can form an important defense strategy against pre-dispersal seed
 predation. The induced mismatches between herbivore and host phenology are
 anticipated to be adaptive when herbivory is predictable across successive
 flowering periods.
description: <b>Study site and
 species</b> The research
 was conducted in the Aelmoeseneie forest, located south of Ghent
 (Gontrode, Belgium). This <i>ca. </i>30 ha forested area
 entails a mix of ancient and post-agricultural forest and has been managed
 as high forest since 1950 (Vanhellemont & Verheyen, 2011). The
 soil consists of sand and sandy loam with alluvial ash forest on the more
 humid parts and acidophilous beech forest on the drier sandy parts. Within
 the forest, we selected ten groups of <i>Geum urbanum</i>
 plants in different locations spread over the forest. A group of
 individuals located close to each other, within a radius of 15 m, was
 considered a ‘plot’. In 2015, 59 plants were marked for detailed
 monitoring (N = 10 plots, 4-6 plants per plot). In 2016, the set of
 monitored plants was expanded with another 50 plants to obtain a larger
 sample size (N=12 plots, 4 – 15 plants per plot). In 2017 only the plants
 from 2016 were monitored. Differences in abiotic conditions, i.e. canopy
 openness, canopy phenology and chemical soil conditions were measured and
 controlled for but none of these variables were correlated with flowering
 phenology, reproductive output or presence of seed predators and could
 therefore be ignored in this study (unpublished data). Plants were monitored once a week
 in 2015 from May until October. Timing of flower emergence was recorded as
 the day of the year and all open unmarked flowers were marked with a
 unique tag to enable identification of individual flowers. Total number of
 flowers per plant could be derived from these data at the end of the
 season. Based on the data of 2015, flowers were monitored on fewer
 occasions in 2016 (July 4, 12, 20, 27, August 12 and September 7; day of
 year 186, 194, 202, 209, 225, 251) and 2017 (July 13, September 19,
 October 18; day of year 194, 262, 291). We observed two flowering peaks
 per season during the three consecutive years of observations and during a
 preliminary study in 2014: high number of flowers in June (around day of
 year 150) and in August (around day of year 225) and a period with fewer
 flowers in between (around day of year 194) (SI 1 in the Supplementary
 Information). This period of fewer flowers coincides with the end of
 predator infection. Because of the bimodality of the flowering phenology
 of <i>G. urbanum</i>, off-peak flowering cannot be
 straightforwardly quantified. We therefore defined off-peak flowering
 relative to the activity period of the seed predators, that is, flowering
 away from the peak in seed predator activity. During the first flowering
 peak, most flowers emerged, and seed predation took place. We hence
 calculated, for each plant, the proportion of flowers that appeared in the
 second flowering peak relative to the total number of flowers produced on
 each plant as a measure of ‘off-peak’ flowering. In 2015 and
 2016, flowers were collected throughout the season when seeds were ripe,
 that is, for each plant we collected flowers on different occasions. In
 2015, few flowers contained beetle larvae, which means that seed herbivory
 was still ongoing. In 2016, flowers were collected slightly later in order
 to ensure that seed herbivory was completed and no larvae were found in
 the flowers anymore. No seeds were collected in 2017. Only flowering
 phenology data were collected to test for lagged effects of seed predation
 on flowering phenology. The seeds from all flowers were checked for
 herbivory by <i>Byturus ochraceus</i>. The number of seeds and
 seed mass was determined separately for predated and unpredated seeds for
 each flower. From these data, we calculated the mean mass per seed for
 unpredated seeds. We used seed mass as a proxy for reproductive output
 instead of the number of seeds, since many flowers contained small seeds
 that were weakly developed. Moreover, we found a strong correlation
 between seed mass and germination probability (unpublished results). As a
 measure of reproductive output per flower, total seed mass per flower was
 calculated as the sum of the mass of predated and unpredated seeds. We
 included the weight of the predated seeds since predation rate could vary
 among seeds from completely eaten (with negligible weight) to minor
 damage, leaving most of the seed intact. Because we have no information on
 the germination probability of damaged seeds, the most conservative
 approach, that does not exaggerate the effect of predation on reproductive
 output, is to add the weight of predated seeds. As a measure of
 reproductive output per plant, total seed mass per plant was calculated as
 the sum of the seed mass of all flowers on that plant. For the analysis,
 we used a categorical variable for predation occurrence at flower and
 plant level with two categories: predated or unpredated (‘predation’
 hereafter). A flower was considered predated if at least one seed showed
 signs of predation and a plant was considered predated if at least one
 flower was predated.